THE CAMBRIDGE ENCYCLOEPDIA OF CHILD DEVELOPMENT

Edited by Brian Hopkins

Extended Glossary

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This glossary represents an extended version of that published in the encyclopedia. Information contained in many terms to be found in the encyclopedia has been expanded. In addition, new terms have been added that were mentioned in the encyclopedia’s published glossary, but which were not defined, and cross-references made among terms. The large number of terms reflects the great diversity of topics that are germane to the study of child development from a multidisciplinary perspective. If you have comments or criticisms of terms in this extended glossary, please contact the editor, Brian Hopkins ([email protected]). Corrections and additions to any of the terms are welcome, and if accepted they will be incorporated and acknowledged as coming from you.

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22q11 deletion (CATCH 22) syndrome: it is a genetic disorder standing for the acronym cardiac abnormalities, abnormal facies, thymic hypoplasia, cleft palate and hypocalcemia, which are its defining phenotypical features. Including the DiGeorge syndrome and more commonly referred to as the velocardio-facial or Shprintzen syndrome, it is associated with a specific abnormality or microdeletion on the long arm of chromosome 22. It occurs in about 1 in 700 births, thus making it one of the most common genetic disorder in humans probably due the fact it covers a number of similar syndromes, and has a 50% chance of resulting in mental retardation. It also associated with major psychoses, but particularly schizophrenia. The 22q11-dependent abnormalities are thought to engender dysfunctioning of the limbic system and to interfere with the interhemipheric exchange of information, thereby predisposing individuals to the syndrome. See Behavior phenotype syndromes, Corpus callosum, Limbic system, Reelin

α-bungarotoxin (α-BTX): a 74 amino-acid,substance that presynaptically blocks neuromuscular transmission. It is one of the so-called curaremimetic a-neurotoxins, which are among the most lethal constituents of venom in the snake Bungarus Multicinctus. These toxins bind with very high affinities and selectivities to the nicotinic acetylcholine receptor (AcChoR), and in doing so block neuromuscular transmission through preventing the depolarizing action on postsynaptic membranes. See Acetylcholine (AcH), Akinesis, Amino acids, Botulinus (or botulinum or botox)

A-not-B task/error: devised by Jean Piaget (1896-1980) to investigate the development of object permanence in infancy, the task involves hiding a desirable object at location A for several trials and then hiding it at a new location B. The error is that infants below about 12 months perseverate in searching at A from where they have successfully retrieved the object several times, sometimes even when the object is visible at the new location B. Introducing a delay imposed between the moment the toy is hidden and the reaching action is initiated before allowing the infant to search increases the difficulty of this task, resulting in perseveration, and suggesting that short-term (working) memory constraints have to be overcome in order to perform the task correctly. Thus, the task requires infants both to hold a retrieval plan in mind, and to suppress a previously reinforced response. See Inhibitory control, Object permanence, Perseverate, Search errors in infancy, Working memory ability: the qualities, power, competence, faculties, proficiencies, dexterities, talents, etc. that enable one to perform a particular feat at a specified time and relative to a particular context or task. See Action, Competence (psychology), Context, Skill (general) abruptio placentae:also known as placenta abruptio, it is premature separation of the placenta from the site of implantation on the inner wall of the uterus before the delivery of the fetus. It is a life- threatening condition for the fetus and occurs about 1 in 500 to 750 deliveries severe cases and 77 to 88 in less severe cases Its causes are generally unknown, except that it can occur in cases of abdominal trauma from, for example, a fall, or with sudden loss in uterine volume due to a rapid loss of amniotic fluid. Risk factors include a past history of abruptio placentae, hypertension, increased maternal age, cigarette smoking, drug abuse and drinking alcohol during pregnancy (more than 14 units per week), and diabetes mellitus in the pregnant woman. See Placenta, Placenta previa absolute distance: the precise metric distance of an object or surface relative to the self. See Relative

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distance abstract reasoning: sometimes referred to as fluid intelligence or hypothetico-deductive reasoning, it is the ability to go beyond what is perceived directly in discovering higher-order relations among stimuli. See Analogical reasoning, Fluid intelligence, Hypothetico-deductive method, Ravens’ Progressive Matrices (RPM), Reasoning (psychology), Reasoning (genre theory) abstractions: in Fischer’s neo-Piagetian skill theory, the fourth and final tier of skill development. Abstractions represent generalized or intangible content and stand in contrast to concrete representations, which refer to things that are tangible, concrete and able to be imaged or imitated. See neo-Piagetian theories of cognitive development, Tiers, Representations (mental) acceleration: linear acceleration is the rate of change of velocity measured in meters per second per second (ms-2). It is the first derivative of velocity. Angular acceleration is the rate of change of angular velocity measured in radians per second per second (ws-2). See Radian, Velocity accommodation: the process of modifying or adjusting an existing scheme or psychological structure in order to act upon or know an object, event, or person. For example, a child accommodates his grasping scheme when he adjusts his hand movements to fit the contours of a particular object. In Piaget’s theory, accommodation must occur in tandem with assimilation in the process of equilibration. See Assimilation, Equilibration, Scheme

Accreditation Criteria for Interdisciplinary Studies in General Education: published in 2000, it is a report by a task force commissioned by the Association for Integrative Studies in response to a request from the Association of American Colleges and Universities. The report, which deals only with undergraduate interdisciplinary education, classifies the criteria into five categories: goals, curriculum evaluation, teaching and learning, the role of faculty and administration. The major issue addressed in the report is how to achieve coherence (i.e., connecting and integrating knowledge, languages and methodologies across disciplines). In the future, it is planned to establish criteria for interdisciplinary studies in graduate education. See Interdiscipline, Interdisciplinarity acetic acid: also called ethanoic acid, it is a colorless organic acid with a characteristic odor. The main acidin vinegar, it is produced by the oxidation of alcohol and plays an important role in metabolism. See Cholesterol, Metabolism

acetylcholinesterase (AcHE): also called cholinesterase, it is a hydrolytic enzyme that regulates the level of acetylcholine at cholinergic synapses and neuromuscular junctions. It serves to stop further postsynaptic nerve impulses by destroying acetylcholine after it is released from the terminal boutons of presynaptic neurons and postsynaptic receptors. See Cholinergic neurotransmitter system, Enzyme, Neuromuscular junction, Synapse, Synaptic cleft acetylcholine (AcH): originally called ‘vagusschtuff’ by the physiologist Oscar Loewi (1873-1961), and first discovered by him in the vagus nerve of the frog heart, it is a white crystalline derivative of choline. As such, it is hormone-like, neurotransmitter protein, produced by cells to create or stimulate central nervous system reactions necessary for life. While being an important neurotramsitter in the central nervous system, it is also the main messenger for motoneurons in the peripheral nervous system, including the autonomic nervous system, and for cholinergic effector synapses. It is a ‘clever’ transmitter in that it functions to activate skeletal muscles and

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to inhibit cardiac muscle. Stored in synaptic vesicles, it is released in a quantal manner in response to calcium ion uptake when a action potential arrives. It diffuses across the synaptic cleft to transmit the nerve impulse across the synapse, and binds to receptor sites on the postsynaptic membrane, after which the ion channels open allowing positive ions to enter the cell that then triggers membrane depolarization. Stimulated by nicotine, and depleted in Parkinson’s disease, it has been suggested that smoking tobacco may delay or even prevent the onset of the disease through the actions of nicotine on the basal ganglia (specifically the mesolimbic dopamine system). See Action potential, α-bungarotoxin ((α-BTX), Basal ganglia, Cholinergic transmitter system, Dopamine, Limbic system, Neurotransmitter, Nicotine, Noradrenergic neurotransmitter system, Parkinson’s disease, Peripheral nervous system (PNS), Synapse, Synaptic cleft, Vesicles acidosis: see respiratory acidosis acrosome: a membrane-bound organelle at the tip of a sperm derived from the Golgi apparatus, which contains lytic enzymes that digest the outer coatings around the egg so that it can enter the ovum and inject its haploid DNA. See DNA, Enzyme, Fertilization, Golgi apparatus, Haploid, Organelle, Spermatozoa actin: a protein that interacts with myosin to form the contractile protein actomyosin in muscles, which is involved in other physiological processes (e.g., cellular movement, maintenance of cell shape) in the form of other contractile elements such as flagella. It can exist in a globular or a fibrous form, and is the most abundant protein in the typical eukaryotic cell, accounting for about 15 percent in some cell types. In fibrous form, an actin filament is about 5 nm wide and 100 um long, and attaches itself to transverse Z filaments in the muscle fiber. See Actomyosin, Adenosine triphosphosphate (ATP), Cytoskeleton, Eukaryote cell (or organism), Extrafusal muscle fibers, Flagella, Intrafusal muscle fibers, Myosin, Muscle fiber action: a goal-directed behavior consisting of different movement components that is carried out intentionally or under voluntary control. Thus, an action is goal-directed while a movement is not. An example is reaching and grasping movements in a prehensile action. Actually, two generally classes can be identified: exploratory (or investigative) actions and performatory (or executive) actions. Infants initially generate exploratory actions, perhaps by a process of trial- and-error learning, and from which emerge performatory actions. Thus, there is a developmental transition from only exploratory actions to both exploratory and performatory actions. See Ability, Action sequences, Exploration, Movement, Trial-and-error learning, Perception-action coupling, Skill (general), Transition action potential: a momentary change or electrical excitation in the voltage difference across the membrane of a neuron that is usually triggered by nerve impulses from a number of other neurons at synapses. It results in an influx of positively charged sodium ions through the cell membrane that results in the impulse being propagated along the axon of the neuron. This reverses its resting potential of about -70 millivolts and altering it to about +40 miilivolts, thereby increasing the permeability of the membrane to sodium ions and enabling the influx of positively charged ions. In turn, this propogates the potential from the axon hillock down the axon at a speed (or conduction velocity) ranging from about 0.1 to 10 meters per second in fully myelinated axons. Luigi Galvani (1737-1798) was one of the first to demonstrate an action potential through contacting a scapel with the sciatic motor nerve of a frog he was dissecting. See Acetylcholine (AcH), Axon, Axon hillock, Myelin

www.cambridge.org/hopkins © Cambridge University Press THE CAMBRIDGE ENCYCLOEPDIA OF CHILD DEVELOPMENT - Extended Glossary A-C action sequences: organization of behavior in time, where specific actions follow one another in various temporal patterns. See Action, Serial ordering action syntax: rules of sequential order among actions that are often hierarchically organized into units and larger blocks, rather as letters, words and phrases in language. See Action sequences, Serial ordering, Syntax action theory: a theoretical approach that views individuals as both products and producers of their developmental histories. Vygotsky’s theory of social development is a prime example of such an action theory See Life course analysis action unit: a term to describe the different facial muscles involved in an expression. The facial action coding system (FACS) of Ekman and Friesen (1978) gives detailed descriptions of all the changes in appearance that accompany each of 44 action units they identified in the face. Attempts have been made to automatically track facial action units by means of motion analysis systems. See Behavior system, Facial expressions action words: words that describe, demand, or accompany action (e.g., brought hired, investigated). See Action, Action syntax, Exception words, Symbols, Symbolic function activation: a concept from neuroscience and connectionism in which the state of a neuron codes information according to a coding principle such as space code in higher parts of the nervous system or rate code in more peripheral parts. More generally, it is taken to be the process by which the central nervous system is stimulated into activity through the mediation of the reticular activating system. See Connectionism, Mesencephalic reticular activating system, Space code principle active intermodal matching (AIM): this concept pertains to Meltzoff and Moore’s proposed mechanism for facial imitation. Facial imitation involves intermodal matching because the infant sees the adult’s gesture, but does not see his own response as his own face remains unseen by him. Facial imitation thus requires matching across different sensory modalities (hence ‘intermodal’). It is ‘active’ because infants correct and improve their responses over successive attempts; the responses do not simply pop out fully formed. See Common coding, Cross-modal coordination, Cross-modal matching, Imitation, Intermodal coordination, Intermodal perception active sleep (also referred to as irregular or REM sleep and state II): that condition of the infant when the eyes are closed, intermittent rapid eye movements can be observed through the eyelids, respirations are irregular and variable in frequency and amplitude, and motor activity varies from apparently random small limb movements to occasionally trunk movements and periods of inactivity. Vocalizations are not present. In this sleep state, however, half-sided smiles (sometimes referred to ‘angel smiles’) can be apparent in young infants. See Behavioral state concept, REM sleep activity-dependent organization: the property of the nervous system to use the pattern of its own activity to wire itself. The central concept is ‘fire together, wire together’, a shorthand term for the Hebbian synapse. See Cerebral cortex (development), Connectionist models, Experience-dependent processes, Hebbian synapse, Self-organization actomyosin: a protein complex synthesized from actin and myosin in skeletal (or striated) muscles that

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when stimulated shrinks and causes muscle contraction, with the energy being supplied by adenosine triphosphosphate. See Actin, Adenosine triphosphosphate (ATP), Myosin, Proteins, Striated (or striped or voluntary) muscle adaptation: in evolutionary biology, the process by which those behavioral or other characteristics of individuals that promote survival in their particular environment evolve through the action of natural selection. Also refers to the outcome of the process. A troublesome concept in evolutionary biology, it refers to the process by which the structure and function of an organism become fitted to its environment in an analogy with a lock and key. It allows the organism to survive and reproduce in its environment. There are two main criteria for some thing to be an adaptation: firstly, it has a common occurrence in a population and secondly, its communality is due to the effects of natural selection. The latter implies that an adaptation has a genetic basis as natural selection operates on genetic differences between individuals via their phenotypes. The term is also used for short-term changes in behavior (e.g., as a result of sensory adaptation), but in these cases it is perhaps more appropriate to talk about ‘adjustments’ as they do not fit the two main criteria for adaptation in the evolutionary sense. Charles Darwin (1809-1882) was acutely aware of the troublesome nature of adaptation in that, while his theory of natural selection could explain the elimination of the ‘unfit’, it had difficulties accounting for the creation of the ‘fit’. The problem still remains: how could any process involving chance (viz., the selection of random mutations) give rise to optimal adaptations? If the raw material on which natural selection operates is derived from random variation, then everything and anything is possible. Thus, a criticism of the Modern synthesis has been that it cannot predict what adaptations are likely to arise, only what has a greater probability of surviving in a given environment after change has taken place. Its lack of predictive power in this respect has led to a renewal of interest in developmental and morphological constraints and the ways they might impose themselves on the potential pathways of evolutionary transformation. In effect, it amounts to restoring a role to embryology in biological evolution as witnessed previously in the writings of Conrad Hal Waddington (1905-1975) and others, and more recently in the emerging synthesis of developmental and evolutionary biology (viz., evolutionary developmental biology). See Baldwin effect, Constraint, Environment of evolutionary adaptedness, Embryology, Evolutionary developmental biology, Modern synthesis, Theory of natural selection, Organism additive genetic effect: genetic influences that operate in an additive fashion (i.e., in which two copies of a risk allele confers twice the risk of just one copy). It is the sum of mostly small effects of the alleles of the many genes influencing a particular trait. See Allele, Gene additive model: a statistical model in which the main effects explain variance of the dependent variable such that the total portion of explained variance is the sum of the portions explained by each individual effect. This is in contrast to an interaction effect, which is based on a multiplicative model. See Analyses of variance (ANOVA) adenine: one of four base molecules that form part of the base pairs of the nucleic acids of DNA, RNA and some nucleotides, as well as their derivatives. In DNA, it is always paired with the purine thymine and in RNA with the pyrimidine uracil. See DNA, Nucleic acid, Nucleotide, RNA, Purines, Pyrimidines, Thymine, Uracil adenosine triphosphate (ATP): a nucleotide molecule that is the supplier of energy for all cells. In animals, it is formed by the breakdown of glucose molecules, usually obtained from carbohydrate intakes in a series of reactions involving hydrolysis. ATPase activity in myosin is

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the driving force behind the contraction of muscles. Dephosphorylation results in a release of energy. See Actomyosin, Creatine, Hydrolysis, Myosin, Nucleotide, Phosphorylation adhesion molecules: involved in forming contacts between cells (focal contacts) and between them and the extracellular matrix. Several families of such molecules have been identified by Gerald Edelman and colleagues, among others. Cell-cell adhesion molecules (CAMS) can be either calcium dependent or independent, the former including cadherins, intergrins and selectins, and which appear to be important in tissue-specific cell-cell adhesion during vertebrate embryogenesis (e.g., in the binding of blastomeres). Calcium independent CAMS include immunogloblin-like proteins termed neural cell adhesion molecules (N-CAMs), which are important in determining the shapes of cells. Most integrins appear to bind cells to their extracelluar matrix, and are also present in the growth cones of axons where they play a role in the guidance of axons during their migration and growth. See Axon pathway selection, Blastomere, Blastula, Cadherins, Cell adhesion molecules (CAMs), Cell locomotion, Embryogenesis, Extracellular matrix, Growth cone, Integrins, Neural cell adhesion molecule (N-CAM) adolescent egocentrism: a self-centered view of the world involving a belief that all the world is looking at you (as if on stage with an imaginary audience), or the feeling of being very special and invulnerable. See Self-perception adolescent growth spurt: the acceleration in the rate of growth in height that starts in late childhood and reaches a maximum (peak height velocity) during adolescence. Rate of growth in height decelerates after the peak and eventually ceases in late adolescence or young adulthood. The growth spurt in girls is estrogen induced, and begins coincidentally with (or just a few months before) the first signs of breasts (the second stage of breast development referred to as thelarche). Many girls have proportionally longer legs relative to the torso during the first year of puberty as growth of the legs (and feet) begins to accelerate first. Growth tends to reach a peak velocity, up to as much as 7-10 cm, midway between thelarche and menarche. With the onset of menarche, it starts to decline, and in the subsequent two years about another 5cm in height is attained, As with boys, this mainly involves growth of the trunk rather than the legs. For boys, growth accelerates more slowly and lasts longer. The outcome is a taller adult compared to females, with boys being on average about 10 cm more in height. Growth for boys begins to accelerate some 9 months after the first signs of testicular enlargement with the peak growth spurt occurring about 2 years after the onset of puberty, attaining a peak velocity of between 8 and 12 cm per year. In contrast to girls, the growth spurt is first evident in the feet and hands, then the limbs, and finally trunk. Adult height and epiphyseal closure are achieved at 17 to 18 years. The slower growth of boys is attributed to testosterone having less of an effect on bone growth and epiphyseal closure than estradiol. See Adolescent voice change, Androgen, Developmental acceleration, Epiphyses, Estradiol, Estrogen, Growth, Menarche, Mid- growth spurt, Non-structural growth models, Puberty, Testosterone adolescent voice change: under the influence of androgens, the change in voice pitch that occurs in adolescent males because of a growth spurt in the larynx. The growth of the larynx is more evident in boys, leading to a drop in the male voice of about one octave. The larger vocal folds of males are probably responsible for them having a lower fundamental frequency. Typically, the voice change in boys takes place before the appearance of noticeable facial hair by months and even sometimes years. See Adolescent growth spurt, Androgens, Fundamental frequency (F0), Larynx, Puberty. Vocal folds

www.cambridge.org/hopkins © Cambridge University Press THE CAMBRIDGE ENCYCLOEPDIA OF CHILD DEVELOPMENT - Extended Glossary A-C adrenal cortex: the outermost layer of the adrenal gland derived from mesoderm situated on top of the kidneys that releases corticosteroid hormones into the blood stream in response to stress. Some cells in the adrenal cortex form part of the hypothalamic-pituitary-adrenal axis. See Adrenal medulla, Androgen, Corticosteroids, Cortisol, Hormones, Hypothalamic- pituitary-adrenal axis, Testosterone adrenal glands: in mammals, they are two triangle-shaped endocrine glands, one each located on top of each kidney. They consist of the adrenal cortex that secretes about 30 different steroid hormones (e.g., cortisol, estrogen) and the adrenal medulla that secretes epinephrine. When the glands produce too many or too few hormones, disease conditions can occur (e.g., Addison’s disease, Cushing’s disease). Also called the suprarenal glands, they are mainly responsible for regulating responses to stress by means of the synthesis of corticosteroids and catecholamines, including cortisol and adrenalin. See Adrenal cortex, Adrenal medulla, Catecholamines, Cholesterol, Corticosteroids, Cortisol, Epinephrine (or adrenalin), Hormones, Steroid hormones adrenal medulla: the innermost part of the adrenal gland derived from neural crest cells of the ectoderm that releases the catecholamine hormones epinephrine (adrenalin) and norardrenalin (norepinephrine) into the blood stream in response to stress and fear. See Adreanl cortex, Adrenal gland, Epinephrine (or adrenalin), Estrogen, Germinal (or germ) layers, Norepinephrine (or noradrenaline), Stress (or adrenal) hormones

Adult Attachment Interview: an instrument developed by Mary Main and co-workers designed to measure individual differences in representations of attachment figures in adults. See Attachment, Attachment theory, Social attachment aerobic respiration: respiration occurring in the presence of oxygen. It ensures that foodstuffs, usually carbohydrates, are completely oxidized to carbon dioxide and water, with the release of chemical energy. Most organisms use aerobic respiration, except bacteria and yeasts. It is contrasted with anerobic respiration. See Anerobic respiration, Krebs cycle affixes: inflections or morphemes attached to either the beginnings (prefixes), ends (suffixes), or middles (infixes) of words. Adding prefixes and suffixes to word roots is a feature of so-called agglutinating languages, one of which is Turkish (e.g., ('bakmak', 'bakıyorum', 'bakıceg˘im' 'bakıceg˘iz'). See Morphemes affordance: a neologism devised by James J. Gibson (1904-1979). Defined as functional possibilities of an object or environmental layout relative to what an individual can do with respect to them. It involves two sorts of properties: objective properties (what something affords depends on its physical characteristics) and subjective properties (what something affords depends in addition on relevant characteristics of the perceiver, such as body size and action abilities). For example, whether a chair affords sitting for an infant will, in part, depend on the size and action capabilities of the infant relative to the height of the chair. The affordance concept derives directly from the concept of organism-mutualism. See Direct realist account, Ecological psychology, Organism-environment mutualism. Perception, Prospective control (psychology) age-crime curve: age differences in the frequency of criminal behavior. What such a curve shows is a rapid increase in deviant behavior during adolescence, followed by an equally rapid decrease in such behavior. Its onset has been attributed to increases in testosterone levels, and to

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environmental influences such as deviant families, deviant peers, and the media. While most political and social scientists agree that the aggregate age-crime curve reaches a peak during late adolescence and declines rapidly thereafter, there are ongoing debates about the theoretical meaning of this trend. See Aggressive behavior, Testosterone agentic processes: in neo-Piagetian skill theory, the capacity to exert control over action, thought or feeling. Infants act as agents soon after birth as they begin to exert control over simple reflexes and action elements. Although individuals exert control over their actions, controlled action always occurs under coactive control of the social context and the biological medium within which agentic behavior emerges and is used. This is the process of epigenesis. See Action, Biogenetic processes, Epigenesis, neo-Piagetian theories of cognitive development aggressive behavior: use of force against someone. The force that is used can take different forms, such as physical, verbal, intellectual, emotional, social, economic, and spiritual. Other than testosterone, other factors that are involved in aggressive behavior include substance abuse, and less obvious ones such as chronic obstructive pulmonary disease, dementia, stroke, and urinary tract infections. At present, there is a concern as to whether exposure to violent video games has an effect on manifestations of such behavior. Then there is the bane of all high- school teachers: passive-aggressive behavior (the use of such strategies as procrastination and willful incompetence). See Age-crime curve, Behavior problems, Bullying, Cingulate gyrus, Conduct disorder, Fighting, Indirect aggression, Prosocial behavior agnosia: complete or partial loss of the ability to recognize familiar objects or stimuli (including faces), usually as a result of brain damage, mostly to the parietal or occipital cortex. In addition to visual agnosia, there is auditory agnosia, an inability to recognize or understand the meaning of spoken words, and olfactory agnosia, an inability to recognize smells. Then there is position agnosia: the failure to recognize the posture of an extremity. Agnosia, which does not involve significant memory loss, occurs in neurological disorders such as strokes and dementia. See Cerebral (or intracerebral) hemorrhage, Cortical lobes, Facial recognition, Occipital cortex (or lobe), Parietal cortex, Prosopagnosia agonist muscle: a muscle in a state of contraction that opposes the action of another muscle termed the antagonist. It is the prime mover or muscle directly responsible for a change in position of a part of the body. It can also be defined as one member of a group of muscles whose line of application produces a given moment at a joint. See Antagonist muscle, Moment of force akinesia: absence of movement, used in reference to conditions or drugs (e.g., curare) that result in immobilization of the embryo or fetus and cessation of spontaneous motor activity. See α- bungarotoxin (α-BTX), Fetal akinesia deformation sequence (FADS), Spontaneous motor activity alcohol tolerance: the ability to metabolize alcohol (i.e., ethanol) differs across cultures. Some 5-20% of Europeans have a genetic variant that metabolizes alcohol must faster than the normal variant, while for the Japanese this figure is around 85%. This difference may account for the finding that both newborns and adults of Mongoloid origin display a greater degree of vasomotor flushing to small quantities of alcohol than do Caucasoids of the same age. On the basis of such findings, it has been speculated that, as with lactose tolerance, culturally-based selection pressures concerning the consumption of alcohol have led to genetic differences between Caucasoid and Mongoloid populations in autonomic responsivity to this beverage. Unlike lactose tolerance, however, the relevance of such population differences in this responsivity for

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behavioral development remains obscure. See Cultural selection, Lactose tolerance alert wakefulness: the condition or state of the infant when the eyes are open and can make conjugate movements to pursue a moving target, respirations are relatively regular but more variable and faster than during quiet sleep, and when the limbs are either at rest except for small movements (inactive alert wakefulness) or they move intermittently in a smooth trajectory. The infant either does not vocalize or makes occasional non-cry ‘cooing’ or ‘babbling’ sounds after about 3 months of age. See Babbling, Behavioral state, Behavioral state concept, Cooing, Wakefulness allele: short for allelemorph, it is a specific gene sequence that is one of a number of different mutated or natural forms of a particular gene or DNA sequence. A single allele for each locus on a chromosome is inherited from each parent. When the alleles of a pair are heterozygous (i.e., two different alleles of the same gene), one is dominant and the other is recessive. The dominant allele is expressed and the recessive allele is masked. Thus, a dominant allele is one that expresses its phenotypic effect even when heterozygous with a recessive allele. For example, if A is dominant over a, then AA and Aa have the same phenotype. A fixed allele is one in which all members of a population are homozygous (i.e., when both copies of the gene are identical), with the consequence that no other alleles for this locus can exist in the population. See Additive genetic effect, Chromosome, DNA, Gene, Mutation allocentric search: search for objects based on external cues from the objects independently of one’s body position or locations of previous successful searches for the objects. Also referred to as allocentric spatial coding. Animal studies have shown that the dorsalateral prefrontal cortex mediates this sort of spatial cognition. In contrast egocentric search involves a viewer-centered (or self-referential), rather than an object-centered, frame of reference. At least in terms of the neural systems involved, findings from animal studies caution against a rigid distinction between these two types of spatial cognition, one that has probably arisen from the persisting tendency to treat perception and action as separate domains. In addition, there have also been challenges to the widely accepted view that spatial development in the first year involves a qualitative shift from use of an egocentric frame of reference to an allocentric one. See Dorsolateral prefrontal cortex, Relative distance, Search errors in infancy allometry: in biology, the study of relationships between size and shape. During mammalian growth, different parts of the body grow at different rates, but in a proportional manner so that body shape is noticeably altered during this period without distorting a recognizable species- characteristic form. Over developmental time, allometric changes take place in the face such that a full-blown ‘baby face’ as described by Konrad Z. Lorenz (1903-1989) is evident in humans at about 2 to 3 months after birth. According to Lorenz, it serves as innate releasing mechanism that triggers protective feelings in older children and adults. Some preterm infants may lack a ‘baby face’, contributing to their risk for abuse. It is also used in evolutionary biology to relate changes in body and brain size. The basic allometric formula is expressed as a simple power function: y = bxk, where y and x are the sizes of respective organs and body parts and b and k are constants. The formula can be given as: log y = log b+k.log x. When y is plotted against x on semi-log paper, estimates can be made of the constants b and k, where k is the slope of the allometric line and b the intercept of this line with the ordinate. See Growth, Innate releasing mechanism, Preterm infant alphabet: a writing system in which the letters for the most part represent single phonemes, although some letters (e.g., ‘x’) represent two phonemes and some phonemes are sometimes

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represented by digraphs (by more than one letter) such as ‘ph’’ as in ‘philosophy’. Transliteration (the mapping of one script onto another) works by extensive use of diagraphs. See Diagraph, Phoneme alphabetic writing systems: those in which there are systematic relationships between letters and sounds at the level of the phoneme. Other writing systems are logographic (e.g., Hanzi in China; Kanji in Japan) and syllabic (e.g., Cherokee syllabary; Katakana in Japan). See Logographic writing systems, Syllabary, Phoneme alpha (α) motoneuron: one of two types of somatic motoneurons, and in fact the largest spinal motoneuron, which innervates extrafusal muscle fibers located throughout a muscle. In addition to voluntary skeletal muscle contraction, alpha motoneurons also play a role in muscle tone, the continuous force generated by non-contracting muscle to oppose stretching. When a muscle is stretched, sensory neurons within the muscle spindle detect the degree of stretch and send a signal to the CNS. The CNS activates alpha motoneurons in the spinal cord that cause extrafusal muscle fibers to contract and thereby resist further stretching. This process is also called the stretch reflex. See also Extrafusal muscle fibers, Extrafusal muscle fibers, Gamma (γ) motoneuron, Motoneuron, Muscle spindle, Muscle tone altricial: species that are born immature at birth, requiring parental care for a relatively long time in order to survive. Human newborns have been classified as motorically altricial and perceptually precocial, but there is mounting evidence against this simplified distinction. See Altricial, Newborn, Precocial, r- and k-selection alveoli: the tiny vesicles or sacs in the vertebrate lungs in which the exchange of oxygen and carbon dioxide takes place. It is a process of diffusion by which oxygen is transported from air in the alveoli (during inspiration), while carbon dioxide diffuses out the blood into the air in the alveoli (during expiration). To aid this process, they have very thin walls that are folded in order to increase their surface area so that rapid gas exchange can take place, and they are composed of squamous cells and those producing surfactant. A lack of surfactant in infants born before term age can give rise to respiratory distress syndrome. Smoking and exposure to other pollutants (e.g., asbestos) can lead to the loss the folds, and thereby create problems with breathing and giving rise to emphysema. See Bronchi, Environmental tobacco smoke (ETS), Emphysema, Preterm infant, Respiratory distress syndrome (RDS), Squamous cells, Surfactant

Alzheimer’s disease: the leading cause of dementia in elderly people, it is a progressive, irreversible, and thus incurable, neurological disease characterized by premature senile dementia that affects brain functions, including short-term memory loss, inability to reason, as well as the deterioration of language and the ability to care for oneself. There is an irreversible loss of neurons in particular brain areas such as the hippocampus and the polymodal association areas. Also, there is degeneration of the middle and smaller cerebral blood vessels at a cellular level. By the end of the disease, most, if not all the cortical brain areas, as well as many sub- cortical nuclei, have two different types of lesions: amyloid plaques and neurofibrillary tangles. It is similar to senile dementia, with the exception that it usually starts in the 40s or 50s. An estimated 3% of people between the ages of 65 and 74 have Alzheimer's, rising to about half those age 85 and over. Worldwide, it estimated that the disease affects 15 million people. It was first described by the neurologist Alois Alzheimer (1864-1915) in 1906, and he published his observations the next year in his monumental tome Alzheimer’s disease. Associating Alzheimer’s name with the disease was due to the anti-Freudian psychiatrist Emil Kraeplin

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(1856-1926), who was responsible for the term ‘dementia praecox’ [or what was later changed to schizophrenia by Eugene Bleuler (1857-1940)] and its distinction from manic depression. See Cell adhesion molecules (CAMs), Cholinergic neurotransmitter system, Hippocampus, Prions, Sensory memory, Short-term memory (STM) and long-term memory (LTM) ambidexterity: a confusing term. It literally means a condition of ‘equal hand’ (ambi) dexterity or skill across a range of tasks. For tasks requiring little if any skill (e.g., scratching one's nose), virtually all adults are ambidextrous. For certain skilled tasks, even writing, many adults, with sufficient practice, might be able to achieve ambidexterity or near ambidexterity. When individuals call themselves ambidextrous, they often are referring to this narrowly-focused skill. However, by ambidexterity, they may mean that they preferentially use (and presumably are more skilled with) one hand on some tasks, their other hand on other tasks. The latter condition is more accurately described as ‘mixed’, ‘inconsistent, or ‘weak left- or right-handedness’. By any of these loose usages, ambidexterity would be fairly common in the population. In its strict and literal sense, however, it is extremely rare. See Handedness, Laterality

American sign language (ASL): a system of communication for deaf people in which meaning is conveyed by hand signals and the position of the hands relative to other body parts. For historical reasons, many of its signs are more closely related to French Sign Language than to British Sign Language. Chimpanzees, gorillas and orangutans have been taught to use ASL, with evidence suggesting that they then seem to communicate with it at the level of a 5-year- old human. Some ape language researchers regard such evidence as rather controversial. See British sign language (BSL) amino acids: organic acids or compounds that form short chemical chains made of peptides and polypeptides that in turn form proteins. Thus, they are the fundamental components of peptides and polypetides and proteins that go to make up all living cells. In various combinations, 20 basic amino acids make up all the proteins in the human body. There are non-essential amino acids that can be synthesized in the body and essential amino acids that cannot, and thus have to be supplied by diet. There are over 500 amino acids in nature, and some of them have even been found in the debris of meteorites. See Creatine, DNA, Peptides, Polypetides, Proteins, Protein-folding problem, RNA amniocentesis: a technique, first used in 1882 to remove excess amniotic fluid, that involves extracting by centesis (inserting a hollow needle through the maternal abdominal wall into the uterus) a small amount of the fluid (usually about 1 cc for each week of pregnancy), and then analyzing the fetal cells from the sample as a means of diagnosing fetal genetic abnormalities or determining the sex of the fetus. Requires the use of ultrasound to locate the fetus. The technique does bring with it a slight risk of miscarriage, with estimates ranging from 1 in 200 to 1 in 400 procedures. See Amnion (or amniotic sac), Amniotic fluid, Chronionic villus sampling amnion (or amniotic sac): the innermost of two transparent membranous sacs that completely surround the developing embryo and fetus. It is partly responsible for producing the amniotic fluid that fills the sac. See Amniocentesis, Amniotic fluid, Chorion, Chronionic villus sampling amniotic fluid: the watery fluid filling the cavity created by the embryonic membranes (amnion and chorion) that surround the embryo or fetus. It is produced by several sources, including a filtrate from maternal plasma, secretion by the amnion, and urination by the fetus. By the end of the

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first trimester of pregnancy, it contains proteins, carbohydrates, lipids, phospholipids, urea and electrolytes. During the second trimester, the fetus ‘breathes’ in the fluid that then facilitates normal growth and the development of lungs and the gastrointestinal tract. Failure to ingest amniotic fluid can lead to hydramnios, which is known to be a threat to the integrity of the developing fetus as, among other things, it can lead to cord prolapse. See Amnion, Cord prolapse, Electrolytes, Hydramnios (or polyhydramnios). Lipids, Phospholipids amodal: intermodal information that is not unique to one sensory channel, as when a single event is specified by more than one modality. Active intermodal matching, Cross-modal coordination, Cross-modal matching, Intermodal perception amygdala: also called the amygdaloid nucleus, it is a key, almond-shaped, bilateral structure in the limbic system of the forebrain involved in emotion recognition and other social emotional functions such as fear, aggression and defensive behaviors, as well as learning and memory. Connected with the prefrontal cortex, hypothalamus, hippocampus and cingulate gyrus. Many common tranquilizing and sedative drugs act on the amygdala. See Anterior commissure, Anterior cingulate gyrus, Autism, Cingulate gryus, Hippocampus, Hypothalamus, Limbic system, Prefrontal cortex analogical reasoning: the process of reasoning on the basis of structural or relational similarity. Much research in cognitive science is devoted to analogical reasoning via, for example, the use of computational modeling. See Abstract reasoning, Analogy (as a trope), Cognitive science, Computational models, Reasoning (psychology), Reasoning (genre theory), Raven’s Progressive Matrices (RPM) analogy (as a trope): a form inductive reasoning or logical inference based on the assumption that if two things are alike in some features, then they are probably alike in other respects. Analogous features are those with similar functions, but not necessarily similar structures. A well-worn example is drawing an analogy between the operation of a (digital) computer and the functioning of the brain. This was done for the first time at the famous Hixson Symposium in 1948 that heralded the birth of information-processing theories, and ultimately the cognitive revolution in psychology and related disciplines. As the example of the Hixon symposium shows, an analogy, like a metaphor, can serve as a preliminary heuristic device in scientific discourse that leads to a final theory. Analogies can be positive, negative or neutral. A positive analogy is where there are features in common between two different levels of organization. A negative analogy refers to the ways in which two levels are not like. A negative analogy reflects ignorance about the features at both levels. Thus, for example, one may ask in what ways metamorphosis is a positive and negative analogy for ontogenetic development, and to what extent it is a neutral analogy. See Analogical reasoning, Analogy (biology), Bridge law (or principle), Heuristic, Hixon symposium, Homology, Isomorphism, Levels of organization, Metamorphosis, Metaphor, Tropes analogy (biology): in 1843, the comparative anatomist Richard Owen (1804-1892) introduced the term into evolutionary biology as he did with homology. It means similarity in function, but not structure, due to convergent evolution. Thus, while the wings of birds and bats do not stem from a common ancestor, they evolved convergently to have the same function (viz., flight) based on different structures (viz., a bird’s wing consists of feathers as against skin in the case of a bat). See Analogy (as a trope), Comparative method, Convergent evolution, Homology

www.cambridge.org/hopkins © Cambridge University Press THE CAMBRIDGE ENCYCLOEPDIA OF CHILD DEVELOPMENT - Extended Glossary A-C analysis of variance (ANOVA): the statistical analysis of mean differences that are traced back to the effects of one or more factors (or independent variables). The simplest ANOVA is a one-way design in which N subjects are (randomly) allocated to a number of different levels of a single factor. Strictly speaking, ANOVA does not analyze variance per se, but rather sums of squares. Thus, the total variation in observations is partitioned into the between-groups sum of squares (between level means), and the within-groups (or residual) sum of squares (differences between subjects in the same group). The desired outcome in most cases is that the between- groups sum of squares is greater than that for the within groups. This is the F ratio named by George W. Snedecor (1881-1974) after Ronald A. Fisher (1890-1962) who originally developed the test. See Error term, Multivariate analysis of variance (MANOVA), Repeated measures analysis of variance, Residuals anaphase: discounting interphase in meiosis, the third stage of cell division in the first division of meiosis (following prophase and the first metaphase). In the first anaphase of meiosis, the paired homologous chromosomes separate and the half chromosomes move to opposite ends of the spindle. In the second anaphase of the second division of meiosis, the chromosomes move apart as in mitosis. Sometimes used for all phases of meiosis and mitosis up to the division of chromatin into chromosomes. See Chromatin, Chromosome, Meiosis, Metaphase, Mitosis, Prophase androgen: first discovered in 1936, it is a male sex steroid hormone in vertebrates produced by the testes and to a lesser extent by the adrenal cortex, such as testosterone, that controls the development and maintenance of sexual organs and secondary sexual characteristics in males. Also called androgenic hormone and testoid. See Adolescent voice change, Adrenal cortex, Hormones, Dehydroepiandrosterone (DHEA), Steroid hormones, Testosterone anemia: a condition in which there is a low red blood cell count in the blood, usually marked by a decrease in hemoglobin, the pigment in red blood cells that transports oxygen. It can be caused by many different conditions, including iron deficiency. Symptoms may include fatigue, weakness, headache, and dizziness. Common in pregnancy, it is usually treatable. See Hemoglobin anencephaly: a congenital malformation due to failure of the neural tube to close at the rostral end, which consists of the absence of the cerebral hemispheres in all cases and of the diencephalon and midbrain in most. Macerated brain stem tissue is visible through a wide defect in the skin and skull and the pituitary gland is usually present although small. The body often shows disproportionate enlargement of the shoulders. A fullterm anencephalic may be stillborn or live for a few hours or days. Its incidence ranges from 1 to 6 per 1000 births and is much more common in males. Some studies have shown that anencephalic infants are capable of a simple form of learning (viz., habiutation). See Congenital malformations, Diencephalon, Habituation, Pituitary gland, Rostral anerobic respiration: respiration occurring in the absence of oxygen. In a process not involving oxygen, it ensures that foodstuffs, usually carbohydrates, are partially oxidized, with the release of chemical energy. The energy yield of this type of respiration is lower than that of aerobic respiration. It occurs in bacteria and yeast as well as in muscle tissue when oxygen is absent. An illustrative example of anerobic respiration is the fermentation of alcohol in which one of the end products is ethanol. See Aerobic respiration

Angelman syndrome: a genetic disorder dominated by learning disability, ataxia, jerky puppet-like

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movements, epilepsy, and various behavior problems, including some autistic features; associated with loss of maternal alleles on chromosome 15q11-13 and other genetic abnormalities. First reported by Harry Angelman (1915-1996) in 1965. See Autism, Behavioral phenotype syndromes, Epilepsy, Prader-Willi syndrome anhedonia: a loss of interest in and withdrawal from all regular and pleasurable activities, often associated with depression. In short, it is an inability to experience pleasure. According to Freud, using his distinction between the id, ego and superego, deficits in the development of the id could lead to anhedonia. It has been suggested that anhedonia may be a marker for patients at risk of schizophrenia or schizophrenia spectrum disorders. See Ego, Id, Pleasure- pain principle, Superego animistic thinking: allegedly typical of ‘primitive’ thinking, it refers to the belief that inanimate objects like rocks possess a soul; the term is often used to refer to magical thinking more generally. Such thinking is a characteristic of children during the Piagetian pre-operational stage of development. See Appearance-reality distinction, Biological knowledge, Theory of the child's mind (ToM) anoxia: total lack of oxygen in inspired gases or in arterial blood, which may cause irreversible damage to nerve cells in the brain. Anoxic anoxia results from defective oxygenation of the blood, in particular the cerebral cortex, and ischemic (reduced blood) anoxia from slow peripheral circulation as can follow a congestive cardiac failure). Hypoxic-ischemic insult follows when there is evidence of reduced blood flow and oxygen. Hypoxic-ischemic encephalopathy is often used by to describe a condition in both fullterm and low birth weight infants, which often presents itself with a variety of medical and neurological problems associated with pre, post or perinatal events. See Birth asphyxia, Hypoxia, Hypoxic-ischemic encephalopathy (HIE), Hypoxemia, Ischemia anlage: an embryonic primordium (clustering of cells) or developmental precursor from which a specific part or organ of the embryo develops. See Embryogenesis antagonist muscle: a muscle acting in opposition to the action produced by the prime mover or agonist, and which is responsible for returning a limb to its initial position. The biceps and the triceps muscles are, for example, antagonist muscles. Thus, when bending the elbow, an action of the biceps, the triceps is the antagonist. In healthy people, the antagonist is inhibited when the agonist is active, a process known as reciprocal innervation. In the cerebral palsies, both can be activated, a process known as co-activation. An important change in motor development is that from co-activation to reciprocal innveration in carrying out movements such as reaching and walking. See Agonist muscle, Cerebral palsies antecedent-consequent relationships: in its weakest form, it is assumed that a precursor or antecedent is simply a forerunner to some later-occurring event in development, without the implication that there is a functional connection between them. In the stronger form, a precursor is a necessary condition for that later event, which would not occur without it. In human development, it notoriously difficult to establish functional connections between earlier and later behaviors in the stronger sense, even when they are seemingly the members of the same developmental sequence. In most cases such connections have been assumed on the basis of similarities in form and timing between earlier and later behaviors. To do so, ignores a class of events termed ontogenetic adaptations: transient age-specific structures and functions that are only adaptive for a restricted phase of development and which may be unnecessary or even incompatible

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with adaptation at later phases. Bowlby’s theory of attachment has been criticized in a similar way. While he regarded adult attachments as a continuation of child attachments, others have argued that latter must disappear before adulthood attachments are possible. See Attachment theory, Necessary and sufficient conditions, Ontogenetic adaptation, Structure-function relationships antenatal: the period during pregnancy from conception to the onset of labor. See Embryo, Fetus anterior cingulate gyrus: a structure in the prefrontal cortex and limbic system that is closely associated with executive attention and executive function. It is activated during conditions of irritation or anger, with extraverted people showing a higher level of activation in the anterior cingulate cortex. In contrast, introverts have less activation in this cortex, but more in the prefrontal cortex. Abnormalities in size, density, and dendritic arborization of neurons in the anterior cingulate gyrus and other areas of the limbic system (e.g., amygdala, hippocampus) have been found postmortem examinations of the brains of people with autism. See Amygdala, Autism, Cingulate gyrus, Executive function, Hippocampus, Limbic system, Prefrontal cortex anterior commissure: a small, round bundle of nerve fibers connected to the corpus callosum that crosses the midline of the brain near anterior limit of the third ventricle. One of three groups of commissural fibers, it connects, like the corpus callosum, the right and left cerebral hemispheres. Its smaller anterior part has fibers that connect the bilateral olfactory bulbs, and a larger posterior part that has a tract between the temporal lobes (as well as connecting these lobes to the amygdala and the opposite occipital lobe). Anterior commissure also refers to the point at the front of the larynx where the vocal folds join. See Amygdala, Cortical lobes, Corpus callosum, Larynx, Olfactory bulb, Ventricle, Vocal folds anterior fontanelle: a diamond-shaped, membrane-covered ‘soft-spot’ situated at the front of the top of an infant’s head that corresponds to the junction of the frontal, saggital and coronal sutures. These fiborous sutures allow movements of the skull plates during delivery through the birth canal, and for brain growth during the first year. Typically, this fontanelle closes (or ossifies) some time between 7 and 19 months, usually in conjunction with the establishment of upright bipedal locomotion. With crying or vomiting, it bulges as it does in cases of increased intracranial pressure due, for example, to hydrocephalus or meningitis. If the infant is dehydrated, this open area shows a depression. The anterior fontanelle (or bregmatic fontanelle) is one of two ‘soft-spots’ on the human newborn’s skull, the other being the posterior fontanelle where the two parietal bones adjoin the occiptal bone, and which closes some 2 to 3 months after birth. See Hydrocephalus, Meningitis, Newborn anthropological veto: the phrase coined by Margaret Mead (1901-1978) to refer to an anthropologist’s ability to disprove universal theories by finding one negative instance. See Cross-cultural psychology, Psychic unity of mankind, Relativism (or cultural relativism), Universalism anthropology: the study of human beings worldwide in relation to distribution, origin, classification, and the relationships between variations in environmental and social influences as well physical characteristics and dietary intake relative to culture. The concept of culture is central to the work of anthropologists and the variations it creates (e.g., in beliefs and many other psychological functions such as social learning, child-rearing practices, development and growth). As a scientific enterprise, it has become a vast area of study in which the major sub- fields are: anthropological linguistics (the study of variations in language across space and time), biological or physical anthropology (the study of primate behavior, human evolution and

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population genetics), cultural or social anthropology (the study of social behavior and beliefs relative to, for example, kinship systems), forensic anthropology (the study of human skeletal variation), medical anthropology (the study of culture-based variations in diseases), and psychological anthropology (the study of cultural variations in a wide range of psychological functions). In the US, archaeology is treated as a sub-field of anthropology, but as a distinct discipline in the UK. In the past, there was a sharp division between the work of anthropologists and psychologists, despite the success of the Torres Straits expedition in bringing together their respective methods and techniques in the study of the relationships between behavior and culture at the end of the 19th century. The division arose as a consequence of the distinction between cultural relativism (held by anthropologists) and the psychic unity of mankind (held by psychologists), a distinction that has waned over the years and led to greater cooperation between anthropologists and psychologists, especially with regard to the study of child development. See Cross-cultural psychology, Culture, Cultural evolution, Cultural selection, Psychic unity of mankind, Psychology, Relativism (or cultural relativism), Sociology, Torres Straits expedition aortic hypoplasia: decreased growth of the aorta, the blood vessel that delivers oxygen-rich blood from the left ventricle to the body. It can involve congenital (or birth defect) coarctation (i.e., a discrete narrowing or constriction the distal segment of the aorta). Found in individuals with Williams syndrome, it is a consequence of supraalvular aortic stenosis, which involves the elastin gene. See Congenital malformations, Elastin (gene), Supraalvular aortic stenosis (SVAS), Williams syndrome

Apgar score: an evaluation of a newborn’s physical status by assigning numerical values (0-2) to each of 5 criteria: 1. heart rate, 2. respiratory effort, 3. muscle tone, 4. response stimulation, and 5. skin color (see table below). A score of 8-10 indicates the best possible condition ( a score of 10, however, is very unusual as most newborns lose one point for blue hands and feet). A score of 5 or less is taken to mean that the newborn needs immediate assistance. It is usually carried out at 1 minute (to assess toleration to the process of birth) and again at 5 minutes (to assess the newborn’s adjustment to the postnatal environment) after birth. An Apgar score by itself reveals only the newborn’s condition immediately after birth, and is not intended to be predictive of later developmental outcomes. Devised by the obstetrician Virginia Apgar (1909- 1974) and published in 1953. See Newborn, Muscle tone, Respiratory acidosis Item 0 1 2 Heart rate Absent Below 100 bpm Over 100 bpm Respiratory effort Absent w, irregular breathing Good, strong cry Muscle tone Limp e flexion of extremities movement, with flexed arms and legs onse to stimulation of No response Grimace sneeze, cough, or pull foot sole away of foot Skin color e pale, pale all over pink, extremities blue Completely pink

Apgar scoring system. bpm: beats per minute aphasia: a communication disorder, acquired as a consequence of damage to the left frontal lobe, left temporal lobe, or both, that affects comprehension, reading and writing, and speech. There are three major forms. In Broca’s aphasia, sometimes referred to as ataxic, expressive or non- fluent aphasia, speech consists of short, staccato-like sentences of a few words in which conjunctions (but, on, or) or articles (a, an, the) are omitted It is caused by damage to Brodmann’s areas 44, 45 and 47 on the lateral surface of the left frontal lobe. With Wernicke’s

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aphasia, sometimes called auditory, fluent, receptive or sensory aphasia, the affected person can speak, most commonly in long, uninterrupted sentences, but the words have no meaning (often being unnecessary or even made-up). This type of aphasia is due to damage to area 22 on the lateral surface of the left temporal lobe. As for global aphasia, it consists of a combination of Broca’s and Wernicke’s aphasia, and thus an inability to communicate by means of speech or to understand the spoken word. A severe stroke may present with global aphasia and then slowly resolve into one of the other two aphasias. Other forms of aphasia are anomic (or nominal) aphasia, conduction aphasia, and transcortical aphasia. See Cerebral cortex (anatomy), Cerebral cortex (disorders), Cortical lobes apical ectodermal ridge (AER): the layer of surface ectodermal cells at the apex of the embryonic limb bud. Considered to exert an inductive influence on the condensation of underlying mesenchyme, and thereby to stimulate elongation of the limb and maintain signals required for patterning the limb. The majority of cell division (mitosis) occurs just deep to AER, and this region is known as the progress zone. See Ectoderm, Induction, Limb bud, Mesenchyme, Mitosis, Progress zone apnea: a pause between breaths in a respiratory cycle, usually lasting between 3 and 40 seconds, and due to obstructions to nasal, oral or tracheal passageways, or by malfunctioning of the brain stem itself. Thus, there are three types of apnea: central apnea (the cessation of both airflow and respiratory effort), obstructive apnea (the cessation of airflow in the presence of continued respiratory effort, and apparently first described by Charles Dickens in 1836), and mixed apnea that contains features of both central and obstructive apnea, either within the same apneic pause or at different times during a period of respiratory recording. It is the most common problem of ventilatory control in the preterm infants. Apnea of prematurity (AoP) is attributed to abnormal breathing control due neural immaturity of the brain stem. Its severity is inversely related to gestational age, and usually resolves itself between 34 to 36 weeks gestational age. See Brain stem, Preterm infant, Respiratory distress syndrome, Sudden infant death syndrome (SIDS, cot or crib death) apotosis (or apoptosis): derived from the Greek word meaning ‘a flower losing its petals’, it refers to programmed cell death and replacement. It is a normal biological process in metazoan development that allows the elimination of unwanted cells through activation of the cell death program. The products of apoptosis are absorbed by neighboring cells. In contrast to necrosis, which is a form of cell death resulting from acute tissue injury, apotosis occurs in an ordered process that generally confers advantages during an organism's life cycle. For example, the differentiation of human fingers requires the cells in between the fingers to initiate apotosis so that the fingers separate. Abnormal control of apoptosis can have serious consequences, leading to a wide range of diseases, including cancer and schizophrenia. See Astrocyte, Cell death, Cytokines, Metazoan, Synapse elimination appearance-reality distinction: the ability to distinguish the appearance of an object or situation (e.g., ‘looks like …’) from its underlying reality (‘really truly is’). For example, a white lamb seen through a red filter appears to be red, but is really white. This ability has been hypothesized to be maturationally constrained as it appears universally between 3 and 5 years of age. This distinction, dealt with extensively by Immanuel Kant (1724-1804), still remains a deep-seated problem in philosophy. See Animistic thinking, Autism, Theory of the child’s mind (ToM) appendicular muscles: skeletal muscles of the appendicular skeleton (126 bones in the human) that move the appendages or distal parts of the body (fins, limbs, wings). Muscles in general are

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classified as either extrinsic or intrinsic. Extrinsic (or axial) muscles have their origins on the axial skeleton or fascae of the trunk (part that is stationary) and insertions (part that moves) on the girdles or bones in the limbs. The intrinsic (or appendicular) muscles have origins on the girdles or proximal skeleton and insertions on the more distal parts. During development, myotomes, behind the head and pharynx, form the appendicular muscles. See Axial muscles, Myotome, Pharynx, Striated (or striped or voluntary) muscle application: empirical testing of implications with regard both to whether any implication actually does work in educational practice and to the extent to which it amounts to an improvement. See Education, Implication apraxia: also known as dyspraxia, ideomotor apraxia or ideational apraxia and first described in detail by Hugo Carl Liepmann (1836-1925), it is a neurological syndrome involving the loss of the ability to perform complex voluntary movements, despite no obvious impairments in the muscles or sensory organs themselves. It occurs in many forms. Apraxia of speech, for example, is a disruption in the ability to perform the skilled oral movements necessary for speech, other manifestations being evident in dressing, gesturing and writing. As with dyslexia, a distinction is made between developmental apraxia and acquired apraxia. There is an overlap (co-morbidity) between dyspraxia and dyslexia, and with attentional deficit hyperactive disorder as well as with Asperger’s syndrome. Developmental apraxia was documented in the 1920s by the neurologist Samuel T. Orton (1879-1948) who also tried to account for developmental dyslexia (and other disabilities such as stuttering) in the same way (i.e., as being as consequence of disordered development of lateralization due to the lack of cerebral dominance). See Asperger’s syndrome, Attentional deficit hyperactive disorder (ADHD), Co-morbidity, Developmental coordination disorder (DCD), Developmental dyspraxia, Dyslexia, Laterality, Stuttering archenteron: a cavity formed during gastrulation by invagination of the vegetal plate cells (in the sea urchin) or involution of cells at the lip of blastopore (in amphibians); it becomes the interior of the primitive gut. See Blastopore, Gastrulation, Induction, Organizer arcuate nucleus: an area of the brain stem thought to be responsible among other things for stimulating reactions necessary for waking and arousing from sleep. It is also present as a collection of neurons in the hypothalamus. where it plays an important role in the development of the reproductive system as it releases pulses of the gonadotropin releasing hormone into the pituitary gland. See Brain stem, Gonadotropin releasing hormone, Hypothalamus, Pituitary gland, Sudden infant death syndrome (SIDS, crib or cot death) arguments: words that are operated upon by predicates. They typically include nouns and pronouns. See Predicates arousal: Generally speaking, it is a term used to denote a state of heightened physiological activity in which there is an increased responsiveness to sensory stimulation or excitability. The relationship between such a state and behavior was encapsulated in the so-called Yerkes- Dodson law of arousal: there is an inverted-U relationship between performance and arousal such that an optimal performance on a task occurs at an intermediate level of arousal, and poorer performances at lower and higher levels. The problem with such a formulation is that it is difficult to pin down exactly the meaning of arousal as it has so many different connotations. Is it a single physiological state or some collection of distinct, but interacting, states? One answer to this question is to hold that there is some generalized arousal state within which

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more specific types of arousal (e.g., fear, hunger, sex) interact in, as yet, some unknown ways. Whatever the answer, the application of the term ‘arousal’ to behavioral states in the developing infant, such that such states are depicted as taking up some position on a continuum of arousal, seems inappropriate. See Attention, Behavioral state concept, Limbic system, Locus coeruleus (or ceruleus), Mesencephalic reticular activating system articulation: the process of producing and modifying airflow above the larynx and voice tone into distinctive connected speech through coordinating movements of the jaw, mouth, tongue and vocal cords. Air flow through the nose can be altered to vary the manner of articulation (e.g., whether it flows freely as in producing a vowel or is impeded as with a consonant). The place of articulation serves to classify sounds (e.g., the part of the palate contacted by the tongue). See Larynx, Speech development, Stuttering articulatory quadrilateral: the four-sided figure whose points are determined by the vowels with the articulatory positions of tongue high and front, tongue low and front, tongue low and back, and tongue low and high. All other vowels are produced within or along the sides of the quadrilateral so defined. See Articulation, Vowels artificial intelligence (AI): also known as machine intelligence, it is problem solving, recognition, and other intelligent-like behavior exhibited by an inanimate device. Computers, and especially programming languages such Lisp, led to an explosion of interest in AI. Examples of the sorts of problems tackled by AI include computer vision, natural language processing and speech recognition. However, the most publicized advances in AI have been made in the field of games playing, the best known example being the supercomputer Deep Blue that defeated the world champion Gary Kasparov in 1997. There are two types of AI: strong and weak. Strong AI, a term credited to the philosopher John Searle, aims at producing computer programs that can truly reason and solve problems, and thus it is sentient or self-aware. It is distinguished in terms of human-like and non-human-like AI. Weak AI does not claim true reasoning or problem solving, but only that programs can act as if they were intelligent. Perhaps the founding father of AI was Alan M. Turing (1912-1954) and its beginnings the Turing test. The term AI was coined by the MIT computer scientist John McCarthy in 1955 who devised the computer program Lisp (1958). It was his paper, presented at the Dartmouth College symposium in that year, which really launched AI as an interdisciplinary field of academic study. See Cognitive science, Computational models, Connectionist models, Cybernetics, Intelligence, Interdiscipline, Neural net, Problem solving, Turing test ascending genital tract infection: one of the most common infectious complications during pregnancy, it occurs when lower genital tract microorganisms (e.g., chlamydia trachomatis, gonorrhea) from the vagina or cervix ascend to infect or cause inflammation of the amniotic fluid, placenta, choriodecidua, chorioamnion, or uterus. It is associated with an increased risk of preterm labor/delivery. In US women aged 20-65 years, about 20% suffer one urinary tract infection per year. See Amnion, Amniotic fluid, Chorion, Preterm birth, Placenta aspartate (or aspartic acid): a non-essential amino acid that is a basic molecule of proteins, and which an excitatory neurotransmitter like glutumate. Along with glutumate, it is one of the most common neurotransmitters in the brain, some of the others being gamma-amino butyric acid (GABA) and glycine, which are both inhibitory in action. Given that it occurs naturally in sugar beets and sugar cane, it has been suggested that aspartate may provide resistance to fatigue and thus promote endurance, but evidence for this suggestion is not decisive. See Amino acids, Climbing fibers, Gamma-amino butyric acid (GABA), Glutumate, Glycine,

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Neurotransmitters, Proteins

Asperger’s syndrome: also known as also known as Asperger's disorder or autistic psychopathy, it is a sub-group on the autistic spectrum. This syndrome and classic autism share the same features, but in Asperger’s language development is normal and cognitive development proceeds on time (in fact, some children with the syndrome display what is known as ‘hyperlexia’, the ability to read at an extremely early age). Prevalence is limited, but it appears to be more common in males. Onset is later than for autism, or at least recognized later. A large number of children are diagnosed between the ages of 5 and 9. First described by the pediatrician Hans Asperger (1906-1980) in 1944, using the term ‘autistic psychopathy in childhood’, he did so independently of Kanner’s description of early infantile autism. The difference between Asperger’s and Kanner’s patients was that those of the former were all identified as having speech. Asperger called children with the syndrome "little professors”, because of their ability to talk about their favorite subject in great detail (and perhaps because of their stilted form of speech), and was convinced that many would use their special talents in adulthood. He followed one child, Fritz V, into adulthood who became a professor of astronomy and solved an error in Newton’s work originally detected as a child. See Autism asphyxial death: a suffocation wherein the organism is mechanically prevented from breathing sometimes due to being wedged between furniture or being pushed against soft materials or objects blocking the air passages. See Apnea, Sudden infant death syndrome (SIDS, cot or crib death) assimilation: the process of incorporating a new experiences or (e.g., a new toy) into an existing scheme or psychological structure. In Piaget’s theory, assimilation must occur in tandem with accommodation, which together form the complementary processes of adaptation. See Accomodation, Equilibration, Scheme astrocyte: one type of a number of different glial cells found in the white and gray matter of the central nervous system (CNS). They are star-shaped, with many processes, and provide mechanical support for neurons by wrapping around them and attaching them to their blood vessels. Also, they serve as the CNS’s ‘garbage disposal service’ (i.e., as macrophages or phagocytes) in that they dispose of potassium ions after intense neural activity and the debris resulting from apoptosis. Traditionally assumed to be ancillary satellite cells in the nervous system, recent research has implicated them in the establishment and organization of both the structural and functional architecture of the brain. See Apoptosis, Glial cells, Radial glia cells asymmetrical tonic neck posture or response (ATNR): from the flexed and symmetrical posture of the supine fullterm newborn, an asymmetry develops in which the upper extremity on the side to which the head is rotated extends, while that on the side of the occiput is flexed (thus being described as a ‘fencing position’). Also, the leg on the side of the face tends to be extended, while the other leg is flexed. If the posture is imposed by passively turning the head, it appears earlier than its spontaneous counterpart. Both reach a peak during the second to fourth months, and then gradually disappear as a more symmetrical posture is regained. The mechanisms are poorly understood, but it is thought that the posture arises from the increasing influence of extensor over flexor neurons. See Posture asymptote: a line on a growth curve that gets increasingly near the ceiling, but does not reach it. An example of an asymptote is the graph of the function f(x) = 1/x, in which two asymptotes are being approached: the line y = 0 and the line x = 0. The curve approaches them, but never

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reaches them. See Exponential, Logistic growth function

‘at-risk’ concept: one implying the probability of an adverse outcome. In developmental research, typically one risk factor (e.g., very preterm birth) is used to predict other risk factors (e.g., cerebral palsy). The term ‘at-risk’ as a medical concept originated in epidemiology, which in turn adopted it from the insurance industry that used it in relation to mathematical determinations of liabilities and insurance premium costs. In both epidemiology and the insurance industry, risk is identified by defining and measuring probabilistic outcomes, and relative to a specific event (e.g., at risk of contracting a specific disease). Medical use of the term implies that treatment or prevention of some kind is required. See Attributable fraction, Epidemiology, Risk factors, Risk mechanisms, Vulnerability ataxia: sometimes referred to as dyssnergia, it is a diminution or loss of coordination over voluntary movements and balance that can result, for example, in a staggering gait. Classified as a type of cerebral palsy, it is due to degeneration of the cerebellum or lesions in other areas of the central nervous system (e.g., in the spinal cord). Its determinants are varied, and examples are: a viral infection (e.g., chicken pox), encephalitis, trauma, stroke, and alcohol and drug abuse. It can also be inherited as an autosomal dominant disease. There are different types of ataxia, classified according to their determinants and location (e.g., gait ataxia, locomotor ataxia, optic ataxia, sensory ataxia). See Autosomal dominant condition/disease, Cerebellum (disorders), Cerebral palsy, Gait athetoid (or athetotiform) movements: those resembling the slow, involuntary writhing movements characteristic of athetosis, and especially evident in the hands and fingers and sometimes in the feet. First described by William John Little (1810-1894) in 1843. Athetoid cerebral palsy (CP) arises from damage to the basal ganglia or cerebellum, and occurs in about 10% of children with CP. Speech is nearly always affected to some degree due to difficulties in controlling the tongue, breathing and vocal cords. In addition, there may be drooling and problems with eating. Mixed CP commonly includes athetoid movements or dystonia or both, and mild spasticity. The movements may be reduced or disappear during sleep, but they are worsened by exercise (e.g., walking) and emotional stress. They may also be evident in Tourette’s syndrome. See Basal ganglia (disorders), Cerebellum (disorders), Cerebral palsies, Dyskinesia, Dystonia, Huntington’s disease (or chorea), Muscle tone, Spasticity, Tourette’s syndrome attachment: a positive social relationship between a child and a parent that fosters feelings of security in the presence of the parent and distress in the parent’s absence. If attachment is secure, then the child can readily separate from the primary caregiver, and actively seeks that person out on his or her return. See Attachment theory, Insecure attachment, Social attachment attachment theory: usually refers to the theory proposed by John Bowlby (1907-1990) and developed further by Mary D. Salter Ainsworth (1913-1999) that is meant to explain how an infant develops emotional relationships with the mother or another caregiver, and how they relate to subsequent development. Attachment behaviors, forming a system, are assumed to be biological predispositions that have evolved to maintain the survival of the species by ensuring the proximity of caregivers committed to providing care and protection during early childhood. The crux of the theory in its present form is the notion of an ‘internal working model’: ways of coping with the world that are developed in response to the responsivity of the caregiver. Such styles may carry through from infancy into the adult’s style as a caregiver. See Adult Attachment Interview, Antecedent-consequent relationships, Attachment, Coping,

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Environment of evolutionary adaptedness attention: there are a number of meanings associated with the term such as visual attention, auditory attention, top-down and bottom-up controlled attention, and so on. In general, it refers to the selective and sustained aspects of perception that focus on certain features of the environment to the relative exclusion of other features. It may be conscious in that some stimulus elements are actively selected out of the total input, although mostly we are not explicitly aware of what leads us to perceive only some small part of the stimulus array. Models of attention often include aspects of selectivity, selecting one item in favor of another, with either the selected one being enhanced, or the other one being suppressed. Other models consider the assignment of resources to items. Another application of the term is joint attention: the process of sharing one’s experience of observing an object or event by following gaze or pointing gestures, and which is assumed to be crucial for cognitive, language and social development more generally. It is interesting to compare this outline with what William James said about attention: “Everyone knows what attention is. It is the taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought. Focalization, concentration of consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others, and is a condition which has a real opposite in the confused, dazed, scatterbrained state which in French is called distraction, and Zerstreutheit in German” (The principles of psychology, Chapter 11, p. 404). Arousal and attention are related, but in a nonlinear manner. While attentional performance improves with a moderate increase of arousal, it drops dramatically when a state of high arousal is achieved. In contrast, sustained attention reduces arousal and induces drowsiness. Furthermore, attention and arousal are based on distinct anatomical systems, mainly cortical for the former and chiefly sub-cortical for the latter. They do, however, share an anatomical substrate, namely, the thalamus. More specifically, as shown in animal research, the relay and reticular neurons in the thalamus undergo a marked alteration in discharge activity with the change from waking (viz., sustained tonic firing) to sleep onset (viz., a bursting mode). See Arousal, Consciousness, Controlled attention, Covert attention, Divided attention, Executive attention, Joint attention, Overt attention, Perception, Pulvinar, Selective attention, Sustained attention, Thalamus attention deficit hyperactivity disorder (ADHD): a relatively common and diffuse childhood disorder, it is a constellation of problems that become manifest in children entering school, characterized by inattentiveness, hyperactivity, poor impulse control, behavior management problems, and a high risk of other co-morbid behaviors and academic problems. First described by Heinrich Hoffman (1809-1894) in 1845, it was not until 1902, following the Coulstonian lectures delivered by the first British professor of pediatrics George F. Still (1861-1941) at the Royal College of Physicians in London, that it was seen as something other than arising from the effects of inadequate child rearing [it has recently been claimed, however, that the first description of the syndrome was made in 1798 by Alexander Crichton (1763-1856), the Scottish physician to the Imperial Russian Court]. Since the beginning of the 20th century, it was variously referred to hyperkinesis, the hyperkinetic reaction of childhood, and hyperactivity. In 1980, the diagnosis of ADHD was formally recognized in the Diagnostic and statistical manual, 3rd edition (DSM III), the official diagnostic manual of the American Psychiatric Association. Estimates of ADHD in the school-age population range from 3% to 5%. Thus, in a classroom of 25 to 30 children, there will be at least one with ADHD. Genetic influences are indicated by the fact that ADHD runs in families (e.g., at least one-third of fathers who had ADHD have children with the syndrome), and that when one identical twin has the disorder there is an increased likelihood of the other one having it. Recent fMRI research focused on

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neurotransmitters in the frontal cortex has indicated that children with ADHD have a more that a two-fold increased level of glutamate (an excitatory neurotransmitter), together with a decreased level of gamma aminobutyric acid (GABA; an inhibitory neurotransmitter). Lower levels of brain glucose metabolism have also been shown in such children by means of PET scans, particularly in the premotor cortex and the superior prefrontal cortex. See Attention, Behavior modification, Brain (neuro-) imaging, Conduct disorder, Co-morbidity, Controlled attention, Functional magnetic resonance imaging (fMRI), Frontal cortex, Gamma aminobutyric acid (GABA), Glutamate, Implusivity, Prefrontal cortex, Premotor cortex, Reification, Ritalin attentional flexibility: the capacity to shift the focus of attention from one task to another. This involves the ability to initiate, focus, sustain, inhibit and transfer attention. This capacity is typically measured by performance on card sorting tasks, in which the sorting rule is periodically changed; impaired performance on such tasks can involve difficulties in disengaging from the previously correct rule or in establishing and attending to the new rule. See Executive function, Wisconsin Card Sorting Task attractions: positive forces that bring persons together, including combinations of behavior and physical features. See Friendships, Repulsions attractor: a particular solution of a dynamical system to which other solutions converge in time. Attractors can be constant in time, periodic, or have more complex time dependencies (e.g., chaos). They are (asymptotically) stable in the sense that the dynamical system evolves such as to approach the attractor in whose vicinity the system starts out. If the state of a dynamical system is exposed to perturbations, then this attractive property reduces deviations from stable states. It is a stable region in a state space to which the behavior of a system is attracted and where it will eventually settle down. It serves to organize the temporal flow of events through a dynamical system, which can be captured by the topologies of a number of geometrical forms that are two-dimensional (fixed-point and limit-cycle attractors) or three-dimensional (quasiperiodic or torus and chaotic or strange attractors). Attractors can have as many dimensions as the number of variables that influence its system. See Behavioral state, Bifurcation, Dynamical system approaches, Chaos theory, Non-linear dynamics, Stability, State space, Synergetics attributable fraction: the proportion of cases of some negative outcome (e.g., emphysema)) that may be attributable to a particular risk (e.g., smoking tobacco). See Epidemiology, Emphysema, Environmental tobacco smote (ETS), Risk factor attributional style: a cognitive style that may be depressive or not and which refers to the interpretation of events (i.e., in a task testing for attributional style, subjects are asked to give reasons why a hypothetical event might have occurred). Such causal attributions may be depressive and pessimistic (global, stable and internal (e.g., “the reason I failed my test is because I’m a stupid person”) or non-depressive and optimistic (specific, unstable and external (e.g., “the reason I failed my test is because at the time I was taking the test, there was a lot of noise outside and I could not focus”). See Avoidance learning, Learned helplessness attrition: drop-out or loss to follow-up of participants in a study because of refusal to continue, failure to locate, or other problems. The concern is that non-random drop-out may make the sample no longer representative of the original population. In studies concerned with evaluating the effects of a particular treatment, attrition can be a major problem. The problem is that participants in

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the treatment group come to dislike the nature of the treatment, resulting in a disproportionate number of them leaving compared to the control group. A resultant statistical problem is how best to account for the missing values. See Longitudinal studies, Multilevel modeling auditory (or acoustic) nerve: the set of neural pathways that communicates between the cochlea and the cochlear nucleus in the medulla oblongata of the brain stem. Also known as the vestibulocochlear nerve, it is in fact either pair of the eighth cranial nerve that supplies the organs of hearing (via the cochlear nerve) and balance (via the vestibular nerve) in the inner ear. Axons of the cochlear nerve synapse in the cochlear nucleus, with the ventral part synapsing on cells of the superior olives of the medulla, both on the same side and on the opposite side. The latter cells allow for the auditory localization of sounds in that they compare the timing of impulses from the left and right ears. The vestibular nerve projects to the semicircular canals that register angular acceleration via the vestibular ganglion. See Cochlea, Cochlear nucleus, Cranial nerve, Medulla oblongata, Semi-circular canals, Vestibular system auditory rote memory: the ability to hear something and remember it verbatim. Individuals with autism typically have excellent auditory (and visual) rote memory. See Autism, Memory autism: a neurodevelopmental condition nowadays conceptualized as a spectrum, involving difficulties in social development, verbal and non-verbal communication, absence of imaginative play, and a focus on unusually strong and narrow interests. In classic autism, about half of all afflicted individuals are mute or speak intelligibly only once or twice in their lifetimes, and about 80 percent of persons with autism are classified as being mentally retarded. What distinguishes them from others with mental retardation is their detachment from the world around them and a lack of understanding of others feelings and emotions, together with a greater likelihood of a cluster of strange behaviors (e.g., odd postures, rocking, hand-flapping, unusual food preferences, avoidance of eye contact, insensitivity to pain, head-banging, and other forms of self-injurious behavior). Apart from Asperger’s syndrome, other disorders sharing some of the behavioral features of autism are the fragile X syndrome and Rett’s syndrome. The birth prevalence of autism is 4.5 for every 10,000 live births, but when all pervasive developmental disorders are considered (including Asperger’s syndrome) the figure becomes 15-20 per 10,000 live births. As with developmental dyslexia, there are data reporting that that three or four times as many boys as girls have autism, but that figure is disputed by some who argue that too few girls are diagnosed with the disorder due to different expectations about what constitutes sex-typical patterns of behavior. Recent research into the biological markers and possible determinants of autism has resulted in a plethora of findings. Inevitably, chromosome 15 and the region known as chromosome 15q11-q13 deletion has been implicated, as it has in Angelman and Prader-Willi syndromes. Another region on chromosome 15 that includes three GABA receptor sub-unit genes (GABRB3, GABRA5, GABRG3 that together form GABA receptors) may also contribute to the development of autism, with the GABRB3 and GABRG3 genes, but not GABRA5, being the leading candidates. Other considerations involve, for example, some sort of autoimmune disorder, high levels of testosterone in the amniotic fluid during pregnancy, Vitamin A deficiency, white matter disorders in the brain, and abnormalities in the cerebellum as revealed by brain imaging (e.g., deficiency of cells in the vermis, reductions in the size and number of Purkinje cells). The latter findings suggest that autistic children may have problems in motor development and motor learning. Despite claims to the contrary, there is no proven treatment for autism. Some form of behavior modification therapy has been tried, but findings are inconclusive, as is the case for the administration of large doses of vitamin B together with magnesium. What is worrying is a seemingly widespread

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tendency to prescribe pharmaceutical agents as a means of treating autism in both children and adults, which include antidepressants, lithium, and Ritalin. Perhaps the first person to describe behavior resembling that of an autistic child was the physician Jean Marc Gaspard Itard (1774-1838) in 1801, with his account of the ‘wild boy of Aveyron’, a feral child who lived in a forest and who Itard called Victor. It appears that the psychiatrist Eugene Bleuler (1857- 1940) came up with the term ‘autism’, meaning ‘aloneness’, to refer to the mental state of ‘schizophrenia’, previously known as dementia praecox, It was borrowed by the child psychiatrist Leo Kanner (1894-1981) who is generally acknowledged as providing the first clinical description of the disorder in 1943, He referred to it as early infantile autism and it became known as Kanner’s syndrome. Those children fitting Kanner’s description appear to constitute about 10% of all individuals classified as having autism, and display behavioral phenotypes noted to a lesser degree in other autistic children (e.g., exceptional memory, fascination with mechanical objects, insistence on uniformity in the environment such as having the furniture always placed in a specific order, and unusual skills in music, art, or computation). Finally, regressive autism in which children appear to attaining developmental milestones at appropriate ages, but then suddenly stop progressing and begin to regress into the classical pattern of autistic behavior, has since 1998 attracted increasing attention due to a British study reporting an association with the MMR vaccine in a sample of 12 children. As yet, there seems to be no end to the controversy engendered by this study, although large-scale studies, especially one in Japan, are beginning to refute the association. See Amygdala, Angelman syndrome, Asperger’s syndrome, Auditory rote memory, Behavioral modification, Birth prevalence, Chromosome, Configural processing, Developmental disorder, Empathizing/empathy, fragile X syndrome, Mindblindness theory, Mind reading, Other mind problem, Prader-Willi syndrome, Purkinje cells, Rett’s syndrome, Systemizing, Testosterone, Theory of the child’s mind (ToM) autobiographical memory: succinctly defined, it is memory for events and issues related to oneself that includes memories for specific experiences and memory for the personal facts of one’s life (e.g., remembering buying your first house). Accordingly, we remember more about events occurring at particular periods in time that define us individuals. What is involved in this type of memory are the following: long-term recollection of general features of an event (what took place?), the interpretations we impose on them (what was it like?), and some degree of recall of a few of the more specific details of the event (what was a particular person wearing?) To date, there are three types of autobiographical memory: personal memory (an image of a single unrepeated event), autobiographical fact, and generic personal memory. The latter two are similar to personal memory, with the exception that they are not image based. When autobiographical memories are vivid, they are referred to as ‘flashbulb’ memories (memory of a situation in which you learned of a very unexpected and emotional event for the first time, in most cases, events with national or international significance). All told, autobiographical memories may represent personal meaning of an event, but with diminished accuracy. Considered by some to be a uniquely human feature, there is some debate as to whether all autographical memories are episodic in nature. From a developmental perspective, some have argued that episodic memory precedes autobiographical memory. See Childhood amnesia, Episodic event and semantic memory, Memory auto-encoder networks: connectionist models in which the input is the same as the target. These models have to learn to reproduce the input on the output layer. Often an intermediate layer has fewer processing units than either input and output layers and so forms a bottleneck. In order to learn the task, the model therefore needs to extract statistical information from the input and form compact internal representations. See Backpropagation, Connectionist

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models autonomic nervous system (ANS): a self-regulating division of the nervous system that controls involuntary functions having to do with the cardiovascular, digestive, reproductive and respiratory systems of the body. It is sub-divided into the parasympathetic and sympathetic nervous systems. The origin of the term ‘autonomic nervous system’ is credited to John Newport Langley (1852-1925) who coined it in 1898 and ‘parasympathetic nervous system’ in 1905. See Central nervous system (CNS), Motoneuron, Nicotine, Parasympathetic nervous system, Peripheral nervous system (PNS), Somatic nervous system (SNS), Sympathetic nervous system (SNS) autoregressive series/model: a specific form of time-series analysis where a score at some occasion on a variable (X[t]) is predictive of (or a linear function of) a score at some later occasion on the same variable (X[t+1]). These models are typically employed in time-series analysis, but they can be useful in longitudinal panel analyses as well. See Longitudinal studies, Panel studies, Time-series autosomal dominant condition/disease: genetic condition caused by one mutated gene located on one of the autosomal (‘non-sex’) chromosomes. One of the parents will usually have the disease as it is dominant in this mode of inheritance. Each child of an affected individual has a 50% chance of being affected, regardless of sex or birth order, and homozygotes for autosomal dominant conditions (individuals with two changed genes) have a more severe form of the disease. See Huntington’s disease, Marfan syndrome, Tay-Sachs disease

avoidance learning: learning to make a response to a warning signal in order to avoid an aversive event. See Attributional style, Learned helplessness axial muscles: striated muscles of the axial akeleton (the bones constituting the head and trunk of a vertebrate body; 80 bones in the human). Most often used to refer to muscles belonging to the trunk, especially those that flex the spine as well as move the thorax and abdomen. Dystonia, often present in preterm infants, involves the axial, rather than the appendicular, muscles. See Appendicular muscles, Dystonia, Prterm infants, Striated (or striped or voluntary) muscle axillary hair: hair in the arm pits (or axilla); a secondary sex characteristic. In puberty, axillary hair usually appears after public hair. In males, its appearance is associated with characteristic body odor, lowering of the voice pitch, and acne. See Pitch, Puberty, Secondary sexual characteristics axon: nerve cell process transporting outgoing or efferent information away from the cell body (or soma) in the form of an action potential toward a specific target (other neurons; gland; muscle) with which its connects by means of a synapse. Sometimes referred to as a nerve fiber. An axon of a motoneuron can be up to a meter long in humans, the longest axon being that of the sciatic nerve running from the base of the spine to the large toe of each foot, and which may extend for a meter or more (compared to the giraffe, this length pales into insignificance, with its primary afferent covering a distance of almost 4 meters from toe to neck). Typically, like dendrites, axons are about a one micrometer in diameter. In vertebrates, axons of neurons are sheathed in myelin. The axons of some neurons branch to form axon collaterals along which duplications of the axon potential travel simultaneously to more than one other cell. The anatomist and physiologist Rudolph Albert von Kölliker (1817-1905) coined the word ‘axon’ in

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1896, and it began to appear as a neuroanatomical term in the early 1900s. See Action potential, Axon collateral, Axon pathway selection, Axon retraction (or pruning), Cell theory, Dendrite, Guidepost cells, Motoneuron, Myelin, Neurite, Neuron, Synapse axon collateral: a branch of the main axon that originates at the node of Ranvier. See Axon, Myelin, Node of Ranvier axon hillock: the conical, tapering area of the axon’s origin from the soma of the neuron containing microtubles and devoid of Nissl substance. It is here that the graded inputs of inhibitory postsynaptic potentials and excitatory postsynaptic potentials from the dendrites are summated to determine if an action potential is generated. It is if the threshold is exceeded. See Action potential, Axon, Dendrite, Nissl substance, Microtubles axon pathway selection: the capacity that the axons of developing neurons have to select particular directions of migration. The first axons to migrate in the embryo are termed pioneering axons that serve as pathways for some, but not all, later developing axons to migrate to their target. They are guided by growth cones at their tips that respond to the presence or absence of growth cues (i.e., protein adhesion molecules) in the extracellular matrix. Such cues, recognized by receptors on the membrane of the growth cues, are short- or long-range, and can be either attractive or repellant. Diffusible chemoattractive substances are secreted by the targets of developing axons, and help to guide the axons to the correct site for synaptic contact to be made. Cells located near the target neurons may also secrete a chemorepellant, resulting in axons being deflected away in the direction of their correct destination, or preventing them from overshooting it. The so-called guidepost cells indicate the end of one pathway, and the beginning of another. See Axon, Extracelluar matrix, Growth cone, Guidepost cells, Synapse elimination axon retraction (or pruning): a phenomenon often seen in early normal development, where axons extend farther, or to more places or terminal zones, than they will at maturity, and then refine their connections by retracting. Despite its ubiquity as a widespread regressive phenomenon in the developing brain that helps sculpt the pattern of neuronal connections, and like synapse elimination, the underlying mechanisms are incompletely understood. Consequently, much research on axon retraction has focused on the neuromuscular junction because of its relative accessibility and simplicity, where it is thought that axons compete for some neurotrophic growth factors, with the ‘losers’ retracting (the so-called neurotrophic hypothesis). The best studied neurotrophic factor is the nerve growth factor (NGF), which is essential for the survival and differentiation of most sympathetic neurons and many, but not all, sensory neurons, but which has no effect on motoneurons. Thus, motoneurons must depend on another kind of neurotrophic factor, and in this respect the glial-derived neurotrophic factor (GDNF) has been proposed. Other factors include brain-derived neurotrophic factor, fibroblast growth factors, neurotrophin-3, neurotrophin-4/5, glial cell derived neurotrophic factor, leukocyte inducing factor (also called leukemia inhibiting factor), ciliary neurotrophic factor, and insulin-like growth factors. See Axon, Brain derived neurotrophic factor (BDNF), Fibroblast growth factor, Glial-derived neurotrophic factor (GDNF), Motoneuron, Nerve growth factor (NGF), Neuromuscular junction, Neurotrophic growth factor (NGF), Neurotrophin NT3, Polyinneration to monoinnervation, Quantitative and qualitative regression, Synapse elimination

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B babbling: non-meaningful sound sequences produced by infants, especially sequences of consonants and vowels that typically appear between 6 and 10 months of age. At first, babbling is relatively unformed. It begins around 5 to 7 months of age, when a infant’s vocalizations start to appear as consonant-vowel combinations called canonical syllables, some of which are repetitive (e.g. “baaa”, “dadadada”, “goo”). Hence, is referred to as a canonical or reduplicated babbling. Later, the infant makes use of repetition and variation of adult sounds in forms such as “bagadig”. There are two competing theories about the functional significance of babbling. In the theory by the linguist Roman Jakobson (1896-1982) appearing in 1968, while the child’s babbling produces almost the full range of possible human speech sounds, it is random and therefore distinct from speech. In contrast, according to the continuity theory of Kim Oller and colleagues (1975), babbling reflects the same substitution and deletion processes appearing in first words (viz., initial stops are more frequent than fricatives and affricates; single consonants rather than clusters). See Alert wakefulness, Babbling drift, Cooing, Consonants, Fricatives, Phonemes, Speech development, Vowel-to-consonant ratio, Vowels babbling drift: the theory that the sounds in infant babbling begin to approximate those of the target language well before the onset of the first words. The process of approximation begins about 9- 14 months. In the past, there were problems in finding data in support of this theory. More recent cross-language studies, however, have suggested relatively early language effects on infants’ babbling behavior. For example, the linguistic origin of babbling samples by six-month- old French and Arabic infants were perceived above chance by a group of French phoneticians. The same result obtained in the case of non-phoneticians for corresponding groups of eight-month-olds. The theory (or hypothesis) was first put forward by the linguist Roger William Brown (1925-1997) in 1958. See Babbling, Language development, Speech development

Babinski response: extension of the big toe upward and the spreading out of the other toes when the external portion of the newborn’s foot is stroked from the back of the heel to base of the toes. Absent when there is damage to the lower spinal cord. First reported by François F. Babinski (1857-1932). See Newborn, Reflex back-translation: the process of exporting a language-based measure (e.g., a rating scale or interview) into a culture using a different language. After translation by a bilingual expert, the result is critiqued by people from the ‘new’ country, and then translated back into the original language by an independent linguist, often a professional translator. The result is scrutinized by the experts in the original country, and the process repeated until there is clear convergence of meaning. See Cross-cultural psychology, Delphi method, Expert opinion backpropagation: the best known algorithm for training neural network models with more than two layers of units. The principle of the backpropagation algorithm is to change the weights in the neural network so that the discrepancy between the network’s output and the desired output (supplied by a ‘teacher’) is minimized. In general, bakcpropagation aids in the prediction (i.e., planning) and control (i.e., reinforcement learning) of large systems, and not just for supervised learning. Compared to other, more traditional methods or error minimization, it reduces the cost of computing elements by a factor N, where N is the number of elements to be calculated. Another advantage is that it allows higher degrees of non-linearity and precision to be applied to neural networks. See Auto-encoder networks, Cognitive-functionalist approach,

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Connectionist models, Neural net balance scale task: a task in which children have to predict the movement of a balance scale that has weights attached on either side of the fulcrum, and where the weights and their distance to the fulcrum vary. Always predicting the correct movement (which side goes down and which goes up) requires sophisticated knowledge of physics (torque), and children progress through three or four developmental stages with characteristic errors. These stages have been modeled in various computational models, as have the nature of the transitions between them. Much of the original developmental research on this task has been carried out by Robert S. Siegler. See Computational models, Force, Physical knowledge, Problem solving, Quantitative and qualitative change, Torque, Transition balanced (or orthogonal) design: ANOVA design in which the cells contain equal numbers of cases. See Analyses of variance (ANOVA)

Baldwin effect: a complex web of arguments, this effect in essence is based on the claim that the ability of individual organisms to learn can influence the process of evolution. Such an influence is achieved by organisms having the genetic pre-disposition for the ability to experiment with potential adaptations, select those that are beneficial for survival, continue to employ them to promote long-term survival, and then to pursue them over less beneficial ones, thus facilitating their long-term survival. Through the cultural transmission between generations of these favorable adaptations or traits, they are maintained in the population. Subsequently, they come under genetic control or some form of epigenetic inheritance, and are passed onto offspring without the original environmental conditions of elicitation being present. While the effect carries Baldwin’s name, it was in fact independently discovered by the psychologist Conway Lloyd Morgan (1852-1936) and the paleontologist Henry Fairfield Osborn (1857-1953). Baldwin himself referred to it as ‘organic selection’ in order to contrast it with natural selection, and with it endeavored to find a theoretical middle ground between Darwinism and Lamarckism while retaining allegiance to the former. For Baldwin, fine motor skills played a significant role in creating the effect because of their inherent phenotypical plasticity arising from variability (or what he termed ‘overproduction’) in the ways they could be performed. With use, the variability is ‘pruned down’ through the process of organic selection, and in this respect having some similarities with Edelman’s theory of neuronal group selection. Toward the middle of the 20th century, Conrad H. Waddington (1905-1975) incorporated the notion of organic selection into his model of genetic assimilation, but without really giving Baldwin sufficient credit. More recently, the Baldwin effect forms a crucial modeling tool in the growing area of evolutionary computation (i.e., artificial life and genetic algorithms) as it attempts to simulate the rapid evolution of the cerebral cortex in general and language in particular. At present, there are those who welcome back the Baldwin effect into the evolutionary fold (the ‘Baldwin boosters’), and those who consider it to be a retrograde step (the ‘Baldwin skeptics’) in that it is perceived as creating a contrived distinction between inheritance and learning. See Adaptation, Genetic assimilation, Epigenetics, Evolutionary developmental biology, Fine motor abilities, Lamarckism, Natural selection, Plasticity (experiential), Theory of natural selection, Theory of neuronal group selection (TGNS) basal ganglia (anatomy): first clearly identified by Thomas Willis (1621-1675) in 1664, along with a number of other sub-cortical structures, it is a complex of five bilateral nuclei consisting of the caudate nucleus, putamen, globus pallidus, sub-thalamic nucleus of Luys (ventral thalamus), and the substantia nigra (pars reticula or the reticulate zone) that also include the compact zone (pars compacta). Sometimes included, especially when making cross-species

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comparisons, are the amygdaloid body (archistriatum), the claustrum, a thin layer of gray matter between the central lobe (lateral sulcus) and the putamen, and the red nucleus (the rubrospinal tract in the midbrain, and not really evident in humans). The globus pallidus and the putamen form the lentiform nucleus (palaeostriatum), and the putamen together with the caudate nucleus make up the corpus striatum (neostriatum). The five nuclei can be grouped into two broad categories based on their input or output connections. The input nuclei are the caudate nucleus and the putamen that receive afferent connections from other parts of the brain other than the basal ganglia (i.e., all areas of the cerebral cortex and the centromedian nucleus of the thalamus). The output nuclei are efferent connections from the globus pallidus (internal segment) and the substantia nigra (reticulate zone) to the thalamus (centromedian and ventral nuclei), and the premotor, prefrontal and motor cortices. Both these output nuclei are inhibitory in function. See Basal ganglia (functions), Cerebral cortex (or pallium), Extrapyramidal system, Metabolism, Motor cortex, Prefrontal cortex, Prefrontal-frontal- striatal loops, Premotor cortex, Red nucleus, Rubrospinal tract, Thalamus basal ganglia (development); relatively little is known about the structural development of the basal ganglia, and what is known is largely restricted to the embryonic period. Cell migration in the sub-ventricular zone and lateral migrations to and from the diencephalon beginning in the fifth week starts the process of forming the basal ganglia, Two weeks later (i.e., by the end of the embryonic period), the basal ganglia are clearly identifiable, and after which development of the cerebellum begins. The corpus striatum (caudate and putamen) develops from neuroblasts situated in the floor of the telelencephalic vesicle (i.e., the striatal ridge). As for the globus pallidus, it originates from neuroblasts in the third wall of the diencephalon, which subsequently migrate laterally to join the corpus striatum. Once the hemispheres have fused, and corticofugal fibers have divided the caudate nucleus from the putamen, the putamen merges with the globus pallidus to form the lentiform nucleus. Thus, much of the basic structural development of the basal ganglia, if not its connectivity, is already achieved during the embryonic period. In late fetal human brains, cells leave the forebrain (diencephalon and telencephalon), cross the internal capsule, and finally end up in the most posterior part of the thalamus (i.e., the pulvinar). Other mammals have no pulvinar (except for the rhesus monkey, which as a small pulvinar), and therefore this migration allowing thlamocortical connections between the basal ganglia and the cerebral cortex does not occur. Thus, it may be the case that the basal ganglia assume functions that are organized differently in most other mammalian species. Despite the basic structure, if not connectivity, of the basal ganglia appearing to be complete already in the embryonic period, their functional development seems to be a protracted process, with most of the evidence for the human being derived from PET scans. Glucose metabolism registered by these scans has been shown to have occasionally high levels in the basal ganglia of the newborn (perhaps state related) relative to the cerebral cortex. A major increase in glucose uptake by the basal ganglia is evident some two to three months later, as it is in the cerebellum (but perhaps slightly later) and the parietal, primary visual and temporal cortices. Interestingly, at this age (or shortly thereafter) a major transformation in behavioral development occurs such that the obligatory-like behavior of the newborn gives way to sensorimotor actions that have a voluntary appearance (e.g., the social smile, first attempts at visually-guided reaching). A pattern of glucose metabolism resembling the adult is evident by 8 months, another age at which a major transformation more germane to cognitive functions occurs in most areas of the brain, including the basal ganglia. See Brain (neuro-imaging), Cell migration, Centrifugal/centripetal, Cerebellum (anatomy), Cerebellum and basal ganglia, Diencephalon, Internal capsule, Neuroblasts, Newborn, Parietal cortex, Primary visual cortex, Pulvinar, Rubrospinal tract, Sensorimotor actions, Sub-ventricular zone, Telencephalon, Thalamus

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basal ganglia (disorders): apart from animal work, disorders of the basal ganglia in humans have revealed much about their structure-function relationships. Such disorders can be classified as hyperkinetic or hypokinetic (and hyperkinetic). Hyperkinetic disorders include ballismus (uncontrolled contractions of the proximal muscles leading to violent movements of the limbs and arising from damage to the sub-thalamic nuclei) and Huntington’s chorea. The best-known hypokinetic disorder is Parkinson’s disease, and another is athetosis. Functional disturbances in the basal ganglia have also been show to play a role in Tourette’s syndrome. See Athetoid (or athetotiform) movements, Brain damage studies, Cerebellum (disorders), Huntington’s disease (or chorea), Parkinson’s disease, Tourette’s syndrome basal ganglia (functions): in the past, the basal ganglia were considered to act as funnels and as an integration center for many cortical inputs. Based on research with rats, this view was changed to one in which the basal ganglia consist of functionally segregated thalamocortical circuits or loops that are involved in the parallel processing of different information. So far, five such circuits have been identified: • motor circuit (see figure below) that plays an indirect role in kinematics, but not dynamics, of ramp movements (viz., their initiation, their direction and the scaling of their amplitude and velocity). An example of a ramp movement is tracking the displacements of cursor on a screen with a hand-held stylus • oculomotor circuit whose main function is the voluntary control of saccadic eye movements (also ramp-like movements) • association circuit hypothesized as having an influence on ‘higher’ mental functions • dorsolateral prefrontal circuit implicated in spatial memory • lateral orbitofrontal (limbic) circuit thought to be involved in the regulation of emotions From this more recent perspective on the functions of the basal ganglia, it can be appreciated that they not only have an important role in motor control, but that they are also ascribed involvement in an array of quite diverse behaviors, many of which were previously thought to be those controlled by the cerebral cortex. In fact, it been said “… the basal ganglia subserve many functions, perhaps all of the functions served by the cortex itself!” [Kandel, E.R., Schwartz, J.H., & Jesell, T.M. (Eds.). (1995). Essentials of neural science and behavior. Norfolk: Appleton & Lange, p. 652). In addition, there are also similarities (and differences) in both connectivity and functions between the basal ganglia and the cerebellum. See Cerebellum and basal ganglia, Cerebral cortex (or pallium), Eye movements, Kinematics, Motor control, Motor cortex

Motor circuit of the basal ganglia. Gpi: internal segment of globus pallidus. SNr: reticulate zone of substantia nigra basket cells: one of three inhibitory GABA interneurons in the cerebellar cortex that together total

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somewhere in the region of 200 million, each one synapsing on the soma and proximal dendrites of 20 or more Purkinje cells that they laterally inhibit via short axons through the release of the neurotransimitter GABA. In in turn, they are excited by granule cells. They are so named because of their tendency to spread out horizontally and straddle such cells in the cerebellum. See Cerebellar cortex, Cerebellum (anatomy), Gamma aminobutyric acid (GABA), Golgi type II cells, Granule cells, Interneurons, Purkinje cells, Stellate cells behavior genetics: the study of behavioral variation among individuals, which is separated into genetic versus environmental components. The most common research methodologies employed are family, twin, and adoption studies. Environmental influences are divided into two classes, shared and non-shared (or unique) environment. The former is the environment shared by siblings reared in the same family, and which includes such variables as socioeconomic status and parent education, while the latter is the environment unique to the individual, and which includes such variables as peer group membership. Supposedly founded by Francis Galton (1822-1911), behavior genetics has come along way since then and its practitioners have devised and developed sophisticated statistical techniques for separating the influences of heredity and shared and non-shared environments on behavior. Problems confronting behavior genetics include definitions of the behaviors in question (e.g., personality traits such as shyness) and the fact that behavior involves multiple genes, something that complicates the search for genetic contributions. In more recent years, with advances in molecular biology, behavior genetics has become engaged in the search for stretches of DNA or locations on chromosomes that are associated with particular behaviors, and which has been successful for mental disorders such as schizophrenia and bipolar disorder. In a sense, some behavior geneticists are cross-disciplinarians in that they have been trained in both genetics and psychology. See Developmental genetics, Environment, Epistatic/epistasis, Hereditary, Heritability, Interdisciplinarity, Interdiscipline, Molecular biology, Non-shared environment, Polygenic mode of inheritance, Polygenes, Quantitative genetic theory, Shared environment behavior mechanism: a hypothetical structure in the central nervous system that, when activated, produces an event of behavioral interest such as a particular perception, a specific motor pattern, or an identifiable internal state. Similar in meaning to cognitive structure. See Cognitive structures, Mechanism, Process behavior variable: a term given a restricted meaning in developmental psychology by Joachim Wohlwill (1928-1987) in his book The study of behavioral development (1973). It is intended to refer to those behaviors most suitable for studying intra-individual differences in development, the key concern of developmental psychology. Two conditions have to obtain: 1. the behavior must be robust enough that age-related changes can be expected to reveal themselves, despite variations in environments and errors of sampling and measurement, 2. these changes must remain invariant over contrasts in specific experiential conditions so that their expected form (i.e., developmental function) under ‘normal’ conditions of development can be determined. Thus, behaviors requiring highly specific training (e.g., factual knowledge) for developmental change to occur are, in Wohlwill’s view, unsuitable for developmental study. Others like emotionality and aggressiveness are better considered as dimensions of individual differences that are independent of development. Behaviors meeting the requirements include motor abilities, visual-motor coordination, spatial ability, attention, memory and language. See Developmental function, Intra-individual differences, Longitudinal studies behavioral embryology: reputedly founded by Wilhelm T. Preyer (1841-1897), it is a branch of

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developmental biology that studies the prenatal development of the nervous system and behavior. Its main animal models are the chick and rat embryo. Among its successes are the Preyer-Tracy hypothesis of autogeneous motility, and more recent studies showing the anticipatory nature of prenatal development, and thus the continuities between it and postnatal development. See Developmental biology, Embryo, Preyer-Tracy hypothesis of autogeneous motility. Self-stimulation behavior modification: in psychotherapy, a treatment approach that uses techniques such as biofeedback, conditioning, reinforcement, or aversion therapy to extinguish or inhibit inappropriate or maladaptive behaviour, rather than remove the causes of such behavior. It can involve social praise, material reinforcers, and tokens, punishment-oriented techniques, including verbal reprimand, and time-outs when the person receiving the therapy has to reflect on the consequences of his or her behaviour. Used in the treatment of children with attention deficit hyperactivity disorder (ADHD). Also known as behavioral therapy See Attention deficit hyperactivity disorder (ADHD), Cognitive behavior therapy (CBT), Reinforcement schedule, Reinforcers behavioral phenotype syndromes: describe behaviors associated with specific genetic or chromosomal conditions, and where these behaviors are related to that particular condition. These syndromes have fairly predictable behavioral presentations and developmental sequelae, and may also be induced by environmental conditions. The term ‘behavioral phenotype’ was first used in a study published in 1972 that attempted to describe the behavioral profile of Cornelia de Lange syndrome (a rare genetic disease, involving chromosome 5, with distinctive facial features and autistic-like behaviors). The behavior phenotypes of some genetic or chromosomal disorders (e.g., Williams syndrome) are not so clear-cut. See Angelman syndrome, Chromosome, Genotype and phenotype, Prader-Willi syndrome. Williams syndrome behavior problems: behaviors that interfere with harmonious social relationships or normal everyday activity (e.g., aggression, hyperactivity, excess irritability). See Aggressive behavior, Conduct disorder, Obsessive-compulsive disorder, Oppositional defiant disorder, Risk factors behavioral state: events intrinsic to the organism that change the probability, direction, and strength of performance. Five behavioral states have been identified in the human newborn. Derived from this classification, four similar states have been shown to be present in the late third trimester human fetus, a taxonomy that excludes crying (see table below). Applying the classification beyond the newborn period is problematic because behavior rapidly differentiates into actions that are no longer match the original state criteria. See Alert wakefulness, Arousal, Attractor, Behavioral state concept, Crying, Newborn behavioral states, NREM sleep, REM sleep

State Body movements Eye movements Heart rate pattern 1F None, but quiescence can Absent FHRP A: small oscillation be interrupted by gross bandwith in which isolated movements that are mostly accelerations can occur startles related to movements 2F Frequent and periodic gross Both REMs and FHRP B: wider oscillation movements that are mainly SEMs continually band than FHRP A, with stretches and retroflexions present frequent accelerations as well as movements of during movements

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the extremities (i.e., general movements) 3F No general or other gross Continually present FHRP C: stable, but with movements present wider oscillation bandwidth than FHRP A and no accelerations 4F Vigorous and continual When observable, FHRP D: unstable, with general movements, they are continuously large and sustained including many trunk present accelerations rotations

Four behavioral states identified in human fetus at 36-38 weeks of gestation. FHRP: fetal heart pattern. REMs: rapid eye movements. SEMs: slow eye movements. States 1F and 2F stand for ‘quiet’ sleep and REM sleep, respectively. It is questionable as to whether States 3F and 4F represent ‘quiet’ and ‘active’ wakefulness, respectively, as they occur in the fullterm newborn. Whatever the case, both have only very short durations relative to the two sleep states. From Nijhuis, J.G., Prechtl, H.F.R., Martin C.B., & Bots, R.G.S..M. (1982. Are there behavioural states in the human fetus? Early Human Development, 6, 177-195. behavioral state concept: this concept can be defined in at least two distinct ways. The taxonomic definition assumes that the classification of states is an arbitrary but convenient heuristic device. It specifies a small number of exclusive combinations among four directly observable state criteria. The dynamical definition assumes that behavioral states are the a posteriori consequences of spontaneous interactions among many fluctuating systems; that they are ‘real’ attributes of the organism, and that only some combinations of sub-systems are dynamically stable. See Arousal, Behavioral state, Sleep-wake cycle, Wakefulness, Dynamical systems approaches, Stability behavior system: any organization of perceptual, central, and motor units that acts as a larger unit in some situations or tasks. See Action unit behaviorism: a school of psychology that studied only unambiguous behavior, which had to be measurable in order to derive scientific laws of human behavior needing only to refer to events that could be objectively defined in physical terms. It left out consciousness and introspection and avoided subjective notions such as imagining. In their place came the claim that learning consists of conditioning. In Russia, it is associated with Ivan P. Pavlov (1849-1936) on conditioned ‘reflexes of the brain’, and in the US with John B. Watson (1878-1958), Clark L. Hull (1884-1952) and Burrhus F. Skinner (1904-1990). See Classical conditioning, Consciousness, Delayed conditioning, Introspective method, Law, Learning, Logical positivism, Operant (or instrumental) conditioning, Radical behaviorism (or environmentalism) beneficence: the obligation upon researchers to maximize possible benefits, and minimize possible harms, for research participants. See Debriefing, Dehoaxing, Risk-benefit ratios bi-directionality: an operation of influences in two directions. So, for example, a parent and child might influence each other during interaction. See Bi-directional relationships, Co-regulation, Interaction, Reciprocity bi-directional relationships: those in which both partners have an effect on one another. This term is used most often to indicate that children have an impact on their parents and on parent-child

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relationships. See Bi-directionality, Interaction, Reciprocity bias (cultural): cross-cultural differences in data that are not related to the trait or concept presumably assessed by an instrument (or some other method), and that tend to distort the interpretation of these data. See Cross-cultural psychology, Method bias, Trait bifurcation: a mathematical term for an instability or transition in a non-linear dynamical system. In such a system, it is a qualitative change in its behavior (order parameter) from one attractor state to another due to a quantitative change at some critical level (a far-from-equilibrium condition) in one or more continuously varying control parameters. Where this change takes place is referred to as the bifurcation point. See Attractor, Catastrophe theory, Control parameter, Dissipative system, Dynamical system, Instability, Irreversible thermodynamics, Non- linear dynamical system, Order parameter, Phase transition (or shift), Qualitative and quantitative change, Transition bilabial: speech sounds (i.e., consonants) formed using both lips, examples of which are /p, /b/ or /w/. They can be voiced (e.g., ‘bill’) or unvoiced (e.g., ‘pill’). See Consonants, Fricative, Glottal, Labio-dental, Lateral sound, Lingua-alveolar (or alveolar), Rhotic sound bimanual task: many tasks must be performed with two hands (e.g., lifting a large two-handled platter of food or a bulky package). Such tasks do not require hand differentiation; each hand (and arm) does essentially the same thing. For assessment of hand differences on bimanual tasks, the hands must be used in different but complementary ways. Examples include opening a jar, where one hand grips and turns the lid while the other hand stabilizes the jar or even turns it in the reverse direction, or painting, where one hand wields the brush while the other holds the palette. There is a fine line between certain unimanual and bimanual tasks. For example, one hand may be sufficient for hammering a nail into wood, but the task initially is bimanual since the other hand holds the nail still until it is securely in place. Likewise, bread can be cut with one hand but, normally, the other hand holds the bread stable. See Handedness, Lateral bias, Unimanual task binocular disparity: also called retinal or visual disparity, it is the small disparity in inputs to the two laterally separated eyes that can contribute to perception of relative depth of nearby objects due to binocular parallax, and thus provides the basis for stereopsis. Binocular disparity is usually described in terms of the two differences between the visual angles subtended by points on an object or surface being viewed, with the visual system being capable of responding three-dimensionally to retinal disparities as small as 2 seconds of arc corresponding to 1/1800 of a degree. The idea that binocular disparity contributes to depth perception originated with the invention of the stereoscope by Charles Wheatstone (1802- 1875) in the 19th century, which he used to show that the brain uses horizontal disparity to estimate the relative depths of objects with respect to a fixed point, a process known as stereopsis. See Binocular rivalry, Binocular vision, Depth perception, Relative distance, Stereoscopic depth perception binocular rivalry: the phenomenon where, if different images are presented to each eye, the perception is not fusion of the two, but alternation between monocular cues resulting in a single coherent perception. The latter is a challenge to the classical view of binocular rivalry (viz., that the two monocular cues are somehow united). The underlying mechanisms, however, remain controversial (e.g., Does it involve competition between monocular or binocular cells? What determines if monocular cues undergo rivalry or fusion?). An emerging view is that it is not the

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physical similarity between images, but the similarity in their perceptual or empirical meaning (at least in adults). See Binocular vision, Depth perception, Binocular disparity binocular vision: also referred to as steorscopic vision, it is an ability restricted to animals with eyes on the front of the head, and involves a combination and comparison of the information received from the eyes, used in the stereoscopic aspect of depth perception, but also in a number of other ways. Binocular vision contributes to depth perception at close distances (within 18-20 feet), but beyond that, the brain relies on less precise cues, such as shadows, and in particular the relative motion of objects at different distances to generate depth information. See Binocular disparity, Depth perception, Stereoscopic depth perception biochemistry: beginning as an interdisciplinary enterprise, it is the study of chemical changes within, and produced by, living organisms. More specifically, it is the study of the chemical reactions and interactions that take place in living organisms, especially the structure and function of their components, such as enzymes, proteins, carbohydrates, lipids, nucleic acids, and other molecules present in cells. See Biophysics, Biology, Inorganic chemistry, Discipline, Enzyme, Interdisciplne, Krebs cycle, Lipids, Nucleic acid, Organic chemistry, Protein biogenetic processes: in neo-Piagetian skill theory, all life processes that function below the level of psychological experience and action. In a hierarchical view of development, organism- environment systems function as multi-leveled processes. Higher levels emerge from integrations of lower-level systems, but have properties that are absent from and not reducible to lower-level systems. As such, while psychological processes (e.g., meaning making, experience, mediated action) are biological processes that occur within a biogenetic medium, a distinction is made between lower-level biogenetic processes (gene action, cell metabolism, brain functioning) and higher-order individual-agentic and socio-cultural processes and systems. See Agentic processes, Emergence, Hierarchy, Levels of analysis, Levels of organization, Neo-Piagetian theories of cognitive development bioinformatics: a rapidly growing interdisciplinary area that draws on computer and information sciences, with a strong foundation in biochemistry, biology, biophysics, chemistry, genetics, and molecular biology. With the aid of advanced computing and statistical techniques, it attempts to manage, process, and make sense of large amounts of data, such as the sequencing of the human genome. It also deals with large databases containing information about the structure and sequencing of proteins in plants and animals as a means of discovering and developing new drugs. Another of its aims is to provide solutions to one of the most difficult issues in molecular biology, namely, the protein-folding problem. See Genomics, Human Genome Project (HGP), Molecular biology, Protein, Protein-folding problem biological evolution: changes in structure and function over successive generations (or across geological time) as a result of a number of mechanisms. These changes may lead to new adaptations within an existing population (microevolution) or those that constitute speciation or extinction (macroevolution). One interpretation is that the changes are a gradual accumulation of small, favorable alterations due to natural selection acting on variability in phenotypes created by point mutations in genes and by genetic recombination (phyletic gradualism). This is the view espoused by the Modern synthesis. An alternative, and more controversial but older, interpretation is that change is more saltatory or catastrophic, and thus accounts for macroevolution in a more convincing way than the Modern synthesis (punctuated equilibrium). While it does not deny the mechanisms upon which the Modern synthesis rests, it stresses as well the roles of random genetic drift in isolated populations and the possibility of mutations in

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whole chromosomes as causal agents in evolutionary change. Enduring debates about the nature of biological evolution include, for example, the mechanisms of speciation and how it might relate to cultural evolution. See Adaptation, Cultural evolution, Cultural evolution and biological evolution, Evolution, Founder effect, Genetic drift, Genetic recombination, ‘Hopeful’ monsters, Macroevolution (horizontal evolution) and microevolution (or vertical evolution, Modern synthesis, Mutation, Phyletic gradualism and punctuated equilibrium, Phylogeny, Speciation, Theory of natural selection biological knowledge: knowledge of biological processes specific to living things, such as growth, metamorphosis, healing, inheritance, illness and contagion. In young children, such knowledge is often expressed partly in terms of ideas derived from animistic thinking. In adults, variations in biological knowledge give rise to differences in opinion about the nature-nurture debate. See Animistic thinking, Physical knowledge biological motion: sometimes referred to as biomechanical motion, it is perception of the motion of independent stimulus elements as part of a moving human or animal figure, as when luminous dots are placed on a walking person and recorded in isolation (i.e., as point-light displays). In particular, the human visual system is very apt at recognizing many aspects of biological, psychological, and social significance in animate motion, suggesting that motion has priority in vision. For example, human motion conveys a wealth of information about the actions, intentions, emotions, and personality traits of a person. How we manage to do this still remains something of a puzzle (i.e., how biological and psychological information is detected in visual motion patterns). One of the issues not entirely resolved is the informational content in point-light displays that enables us to use biological motion in this way. Much of the original work on this topic is due to the work Gunnar Johansson in the 1970s that he first published in 1973. See Motion perception, Perception, Point-light display biological risk factor: biological conditions of the child (e.g., appearance), and influences on the child’s health status, particularly the nervous system (e.g., prenatal teratogens, preterm birth, illnesses) that increase the probability of the child’s physical and/or psychological vulnerability. See Social risk factor, Teratogen, Vulnerability, Preterm birth, Vulnerability biology: the branch of science that studies the characteristic mechanisms, processes and phenomena of living organisms from the molecular to the functional levels of organization. While the boundaries and sub-divisions within it are fluid, it can be depicted as covering biophysics, cellular biology, developmental biology, evolutionary biology, functional biology and molecular biology, and more recently bioinformatics. The introduction of the term ‘biology’ is usually accredited to Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck (1744-1829), but it also appeared in the same year (1802) in the writings of Gottfried Reinhold Treviranus (1776- 1837). Even earlier claims for having coined the term are assigned to Karl Friedrich Burdach (1776-1847) in 1800, and Michael Christoph Hanov (1695-1773) in 1766. See Biochemistry, Bioinformatics, Biophysics, Developmental biology, Developmental genetics, Discipline, Evolutionary biology, Levels of organization, Molecular biology biomechanical degrees of freedom: refers to the number of independent variables necessary to characterize the movements of a limb or an action system. It is those variables that are free to vary, and which provide a means for achieving motor equivalence. See Degrees of freedom (or Bernstein’s) problem, Equifinality, Motor equivalence

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biomechanics: the study of the mechanical and physical basis of biological systems, with particular reference to Newton’s laws of motion and his law of universal gravitation. In terms of muscle biomechanics, Nicholas Stenson (1638-1686), also known as Steno, was the first person to put forward a theory about the generation of muscle force (viz., it was generated as the sum of total forces produced by the sub-units of the parallel fasciles). Biomechanics is better regarded as a methodology, rather than a discipline. See Force, newton, Newtonian (or classical mechanics), Newton’s law of motion, Newton’s law of universal gravitation biophysics: an interdisciplinary branch of biology concerned with the application of physical principles and methods to the study of the structures and functions of living organisms. Most of the research traditions in biophysics were put into place through the work of PhD students in physics during the first half of the 20th century, a prime example being Max Delbruck (1906- 1981) who shared the Nobel Prize for Physiology or Medicine in 1969 for discoveries concerning the replication mechanism and the genetic structure of viruses. Today, biophysicists can be found working in biochemistry, molecular biology, and neuroscience. See Biology, Biochemistry, Discipline, Interdiscipline

Bio-X project: established in 1999 at Stanford University on the promise of $150 million donation from Jim Clark, founder of Silicon Graphics and Netscape Communications, the future of the project was threatened in 2001 when Clark held back $60 million in protest against George W. Bush’s imposition of restrictions on human embryonic stem cell research. The university continued with the project after receiving the amount withheld from a second anonymous donor. In its present instantiation, the project is designed to forge multidisciplinary collaboration in both research and teaching across a number of humanities and science disciplines, but which has a strong biomedical foundation. This is reflected in the construction and completion of the James H. Clark Center for Biomedical Engineering and Sciences in 2003 on the Stanford campus, which is designed as the hub of the project, and to house 42 faculty members, as well as 600-700 researchers and support staff in 225,000 square feet of space. Fellowships are offered for a three-year period during which time they do not have to teach or apply for grant so they can work full-time on their research. An important focus of the project, but by no means the only one, is research addressing the protein-folding problem. Where the humanities fit into the scheme of things is not clear, except or some loosely formulated commitment to dealing with social ethical issues in biomedical research. Stanford, while the first to implement such an ambitious program of multidisciplinary research, is now not alone. Similar models of ‘big science’ have come to fruition with on other major university campuses. One is the Harvard Bauer Center for Genomics Research (http://www.cgr.harvard.edu/), another is the University of Washington Genome Sequencing Center (http://genome.wustl.edu/), and yet another is the Genomics Research Building at Duke University (http://news.mc.duke.edu/gallery/detail.php?id=1291), while MIT has committed itself to the Computational and Systems Biology Initiative. In addition to these university-led initiatives, the Swiss pharmaceutical company Novartis via the Norvatis Research Foundation has come up with $250 million to establish a Genomics Research Institute in La Jolla (http://web.gnf.org/index.shtml), which will work in collaboration with the likes the Scripps Research Institute. Without substantial contributions from philanthropists, it is hard to see all these initiatives being sustained at their current levels of commitment, given the rather precarious state of the US economy at the moment. As for Europe, bundling together such a broad range of scientific disciplines on such a large scale is probably beyond the reach of individual countries, and if deemed desirable (a question raised by some scientists), it would require cross-national cooperation backed, for example, by substantial EU funding. As for

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disciplines such Psychology, the only recent and comparable, but much smaller-scale, enterprise is the Institute for Learning and Brain Sciences at the University of Washington Seattle (http://ilabs.washington.edu/), co-directors Patricia K. Kuhl and Andrew N. Meltzoff, which was initially funded by an anonymous donor. See Genomics, Interdisciplinarity birth asphyxia: a vague term referring to the process whereby hypoxia occurring during the intrapartum period causes some chronic ill effect, the duration or severity of which is not specified but understood to be more than the expected compensatory responses. Some factors, such as acidosis or fetal distress, are followed by abnormal neurological signs, and hypoxic damage to other organs may be consistent with birth asphyxia, but they are not specific to it and can be indicators of damage occurring before labor. See Anoxia, Hypoxia, Hypoxemia, Respiratory acidosis birth prevalence: cases of a specified condition that can be identified by a given age. Excludes cases that cannot be ascertained because they die before the condition is recognized, as well as those that outgrow the condition by the given age and those who migrate in. Includes cases who die after being diagnosed and those who migrate out. Rates are calculated using live births or neonatal deaths as the denominator. See Incidence, Neonatal death, Prevalence blastomere: a totipotent, undifferentiated cell produced by cleavage of a fertilized egg up to the last blastula stage of early embryonic development. It is blastomeres that are used for in-vitro fertilization. See Blastula, Cleavage, Embryogenesis blastopore: a temporary opening on the surface of gastrula through which the internal cavity (the archenteron) communicates with the exterior. Its dorsal lip in amphibians was shown by Hans Spemann (1869-1941) to be the site of induction of overlying tissue during gastrulation. It is the source of the dorsalizing proteins chordin and noggin that bind to the ventralizing protein BMP- 4. See Archenteron, Bone Morphogenetic Proteins (BMPs), Chordin, Gastrula, Hensen’s node, Induction, Noggin, Organizer blastula: the first stage in the development of an embryo, formed by cleavage of the zygote. It consists of a hollow sphere containing undifferentiated dividing cells (blastomeres), which form a layer (blastoderm) around a central cavity (blastocoele). In mammals, the embryo at this stage is referred to as the blastocyst. See Blastomere, Cleavage, Embryogenesis, Zygote

Bock’s profile analysis: a variant of multivariate repeated measures analysis of variance, in which time- adjacent means are compared. See Multilevel modeling, Repeated measures analysis of variance body awareness: attention directed to human bodies, including both one’s own and that of another person. This awareness can concern either the features/appearance of the body or the dynamics of human body movement and posture. Sometimes body awareness is restricted to proprioception. See Kinesthesis, Proprioception

Bone Morphogenetic Proteins (BMPs): members of the transforming growth factor-beta (TGF-b) superfamily of proteins that have been shown to play important roles during embryological growth and development of many different organ systems (particularly the patterning of ventral mesoderm), as well as in tissue repair in postnatal life. Since 1988, more than 16 different human BMPs have been identified. Recent studies have suggested that only some of these BMPs are osteoinductive (i.e., capable of inducing bone formation), with the most

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osteoinductive members of the family being BMP-2, BMP-6, and BMP-9. See Chondrification, Chordin, Induction, Mesoderm, Noggin, Protein

Blood Oxygenation Level Dependent Contrast (BOLD signal): the blood oxygen level dependent signal that serves as the basis for current methods in fMRI. First used to generate functional images of the human brain in the early 1990s, BOLD fMRI uses the intrinsic paramagnetic signal of deoxyhemoglobin (dHB) to detect local hemodynamic changes in blood flow associated with neuronal activity. Because it is strongly paramagnetic and is present in the draining veins after oxygen has been unloaded in the tissues, dHB can be used to depict changes in blood oxygenation, unlike oxyhemoglobin, the main hemoglobin in arterial blood, that has no substantial magnetic properties. Put another way, dHB exerts magnetic susceptibility effects on local tissues, which are detected by T2 signal-weighted images as decreased signal intensity. In contrast, oxyhemoglobin is diamagnetic, and thus has little effect on such images. With neuronal activity, the disproportionate increase in local blood flow in a sense dilutes the amount of dHB, which in turn leads to a positive signal on T2 signal-weighted images. Thus, for example, during cognitive tasks, regional cerebral blood flow, and therefore the rate of oxygen delivery, has a proportionally higher increase than does local oxygen consumption, resulting in a decrease of paramagnetic dHB content in the draining capillaries and veins. As dHB increases magnetic field strength, it creates intra- and perivascular field gradients, spin-phase coherence loss on T2 signal-weighted pulse sequences, and a consecutive attenuation of MR signal intensity. Correlations between the time course of the BOLD signal and performance on the task identifies those brain regions showing task-related changes in the signal. Given that the BOLD effect is due to the deoxygenated blood in the draining veins, the spatial localization of the region where there is increased blood flow resulting in decreased oxygen extraction is not as precisely defined as the morphological features in MRI. Instead, there is a physiological blurring such that it is estimated that the linear dimensions of the physiological spatial resolution of the BOLD signal are around 3 mm at best. See Deoxyhemoglobin (dHB), Functional magnetic imaging (fMRI), Oxyhemoglobin, T2 signal-weighted (T2-W) technique boss (or bride of sevenless): the gene coding for the sevenless ligand and required for the development of the R7 cell in each ommatidium (one of the single eyes forming the compound eye) in the fly eye. More specifically, activation of a membrane receptor tyrosine kinase (sevenless) in the R7 precursor by the ligand bride of sevenless present on the surface of R8 triggers a transduction cascade mediated by ras, thereby establishing the R7 fate of this cell. See Developmental genetics, Ligand, Ras, R7 and R8 photoreceptors, Sevenless, Tyrosine kinase receptor/pathway botulinus (or botulinum or botox): toxin injections made from a chemical produced by bacteria that temporarily paralyze muscle by acting on nerve impulse transmission. They produce reduction of hypertonicity by reversible denervation. Although this toxin exerts this effect on most nerve cells, it acts preferentially on cholinergic nerve endings. Dose-response experiments indicate that the vertebrate neuromuscular junction is the site that is most sensitive to its action. The toxin was first identified in 1897 as the cause of the type of food poisoning subsequently known as botulism, but it was only was in 1949 that botulinum toxin type A was shown to block signals at the neuromuscular junction. See α-bungarotoxin (α-BTX), Cerebral palsies, Cholinergic neurotransmitter system, Denervation, Cerebral palsies. Neuromuscular junction brachial plexus: a group of nerves formed from vertebral levels C5- T1 in the spinal cord that are responsible for innervating most of the structures in the upper limb. See Spinal cord

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brain (or encephalon): the part of the (verterbrate) central nervous system that includes all the higher nervous centers. Enclosed within the skull, it is continuous with the spinal cord and composed of gray (neurons) and white matter (myelin). It consists of three major divisions, each with sub- divisions, and related structures (see table below).

Major divisions Sub-divisions Structures Neocortex, Basal ganglia, Amygdala, Telencephalon Hippocampus, Lateral ventricles Prosencephalon Thalamus, Hypothalamus, Epithalamus, (Forebrain) Diencephalon Third ventricle Mesencephalon Tectum, Tegmentum, Cerebral aqueduct, Mesencephalon (Midbrain) Superior and inferior colliculi Metencephalon Cerebellum, Pons, Fourth ventricle Rhombencephalon Mylencephalon Medulla oblongata, Fourth ventricle

Major divisions of the brain

In vertebrates, such as fish, reptiles, and amphibians, the cortices have less than six layers of neurons, something that is referred to as an allocortex. The brain is separated from the skull by the meninges, a system of membranes, covered by three layers consisting of duramater, arachnoid and pia mater, and suspended in cerebrospinal fluid. The adult brain contains about 100 billion neurons making 100 trillion connections, with the cerebral cortex accounting for about 77% of the total volume of the brain, and which has an estimated 22.8 billion neurons for males and 19.3 billion for females. On average, we lose some 85,000 neurons per day at a rate of about 1 per second. Furthermore, the left hemisphere has 186 million more neurons than the right hemisphere. The blood flow through the whole brain is about 105 ml/100 gm/min in the young child, decreasing to about 54 ml/100gm/min in the adult. Broadly speaking, the brain is the organ whose primary function is to achieve coordinated behavioral outcomes and decisions for selection. It might be said that nothing in the brain (or nervous system more generally) makes sense except in light of behavior. In this respect, one of the continuing debates about brain-behavior relationships is whether function is localized in particular areas (e.g., as modules) or distributed throughout different regions. In the human, mean brain weight is about 1350 grams for the adult (about 2% of total body weight) and 335 grams for the newborn (about 10% of body weight). Compared to other non-human primates, the human newborn has a smaller brain growth advancement. Unlike neonatal body advancements, those for brain growth show marked inter-species differences (see table below). For example, the chimpanzee (Pan troglodytes) has an advancement factor at birth of about 35%, while for the human this figure is about 25% of the adult weight. Such a difference, in which just less than 75% of human brain growth is postponed to postnatal life, may in part explain the differences in behavioral maturity between humans and other primates at birth. See Altricial, Central nervous system, Central nervous system (CNS), Cerebral cortex or pallium), Cerebral cortex (functions), Cerebrospinal fluid, Delivery position (or presentation), Mesencephalon, Metabolism, Metencephalon, Mind-body problem, Modularity, Myelin, Neuroblasts, Newborn, Neuron, Precocial, Prosencephalon, Telencephalon

Neonatal Neonatal Adult Adult Pregnancy Brain growth Body growth Species brain body brain body duration advancement advancement weight weight weight weight Pongo 270 129 1500 343 36, 900 0.376 0.041

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pygmaeus Pan 230 128 1560 360 45, 000 0.356 0.035 troglodytes Gorilla 265 227 1750 406 140, 000 0.559 0.013 gorilla Homo 270 335 3660 1300 65, 000 0.258 0.056 sapiens

Representative pregnancy durations (days), neonatal and adult brain and body weights (grams), and advancement factors for three of the great apes and humans. Data based on Sacher, G.A., & Staffeldt, E.F. (1974). Relation of gestation time to brain weight for placental animals: implications for the theory of vertebrate growth. American Naturalist, 108, 593-615. Pongo pygmaeus: orangutan. Pan troglodytes: chimpanzee. brain damage studies: used to help determine the functions of parts of the brain; a person with damage to a specific brain area often shows deficits in specific abilities (e.g., damage to the hippocampus leads to deficits in memory). See Basal ganglia (disorders), Cerebellum (disorders), Cerebral cortex (disorders) Hippocampus brain derived neurotrophic factor (BDNF): in contrast to nerve growth factor (NGF), BDNF is mainly, though not exclusively, localized in the central nervous system. It supports the survival of primary sensory neurons originating from the neural crest and ectodermal placodes that are not responsive to NGF. See Axonal retraction, Ectoderm, Embryogenesis, Nerve growth factor, Neural crest, (NGF),Placode brain (neuro-) imaging: identified by two broad categories: structural and functional imaging. Structural imaging evolved from radiographic techniques for imaging the brain through non-invasive techniques such computerized axial tomography (CAT) to two-dimensional structural magnetic resonance imaging (sMRI). Functional imaging, which began with xenon gas inhalation, really started to develop with the discovery of radioligands that remained in the blood stream or entered the brain to bind to certain receptors, which gave rise to single photon emission computerized tomography (SPECT) and positron emission tomography (PET). A subsequent breakthrough came with the development of oxygen-15 labeled water (H215O or H20-15) imaging. H20-15 emits positrons and creates images based on regional blood flow within the brain. Since active neurons recruit a robust blood supply, H20-15 PET allowed regional maps of brain activity to be made during a variety of cognitive tasks. When it was discovered that blood flow changes could be measured by H20-15, functional magnetic resonance imaging (fMRI) appeared on the scene. Instead of radiation or X-rays, MRI uses variation in the signal produced by the body’s protons when it is placed in a strong magnetic field. Other imaging or brain mapping techniques include electroencephalography (EEG), magnetoencephalography (MEG) and optical imaging. See Blood Oxygenation Level Dependent Contrast (BOLD signal), Diffusion tensor imaging, Diffusion tensor magnetic resonance imaging, Electroencephalogram (EEG), Electromagnetic fields (EMs), Event-related brain potentials (ERP), Functional imaging, Functional magnetic resonance imaging (fMRI), Ligands, Magnetic resonance imaging (MRI), MRI morphometry, Neuroimaging studies, Optical imaging, Structural imaging, Structural magnetic resonance imaging (sMRI) brain sparing: a notion derived from animal studies. which claims that when the developing organism is subjected to perinatal insults such as hypoxia, then the supply of oxygen and nutrients is preferentially directed to the brain at the expense of other vital organs like the kidneys and liver. Recent research, including that with preterm infants suffering from intrauterine growth retardation, has questioned the validity of this claim. In another vein, we have the Kennard

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Principle or Doctrine, named after Margaret Kennard (1899-1976) who was perhaps the first to demonstrate behavioral sparing following lesions to the motor cortex in neonatal monkeys during the 1930s. She established the modern era of research on brain sparing and functional recovery by showing that a number of factors, and not only lesions, can affect post-injury performance. In addition, she recognized that if neural re-organization does occur, then it probably happens in the damaged parts of the nervous system. See Hypoxia, Intrauterine growth retardation (IUGR), Plasticity (neural), Preterm infant brain stem: an evolutionary older, more ‘primitive’ part of the lower central mammalian brain responsible for organizing fundamental emotions related to fear, hunger, sex, protective drives and temperature control, emotionality, arousal, sleep, heart and breathing rates, water retention, blood pressure and volume, as well as possibly the ratio of carbon dioxide to oxygen. See Cranial nerve, Medulla oblongata, Mesencephalic reticular activating system bridge law (or principle): also known as reduction function, it is a law (or set of laws) connecting the predicates of the reduced theory (the theory to be reduced) with the predicates of the reducing theory (the theory to which the first is reduced). First introduced by Ernest Nagel (1901-1985) as a means of integrating different levels of organization in a supratheoretic system and thus a step toward the achieving the unity of science (i.e., a Theory of Everything), he held that one theory could be reduced to another if it was possible to logically derive the first from the second, together with bridge laws. One claim for a bridge law that has been made is self- organization, something that is evident at all levels of organization. Under restricted circumstances, Nagel’s approach has been shown to work, as in the case of reducing the theory of optics to the theory of electromagnetic radiation (viz., light waves are electromagnetic waves). In other instances it has not as, for example, with regard to attempts at reducing classical thermodynamics to statistical mechanics, because the latter does not contain any non-statistical features that relate to temperature. Attempts to find bridge laws between psychology and neuroscience has so far not been achieved in a convincing, manner, except perhaps with the concept self-organization. All told, today there is very little adherence to searching for bridge laws, except perhaps within restricted domains of physics. One alternative proposed is to start with analogies and then to see if they can be worked up to the status of bridge laws. Certainly, analogies offer a better departure point for establishing interdisciplinarity than do bridge laws. See Analogy (as trope), Classical thermodynamics, Deductive- nomological model of scientific explanation, Interdisciplinarity, Levels of analysis, Levels of organization, Psychology, Neuroscience, Reductionism, Self-organization, Theory of Everything (ToE)

bridging: in neo-Piagetian skill theory, a change process in which persons use a target skill (called a shell) to guide their construction of a new skill. People use the higher-level target like an algebraic equation in action, a target with unspecified components that are used to shape and direct the development of lower-level skills. In this way, the higher-level target serves as a bridge in the construction of the lower-level components to form a new skill. See Constructivism, Levels of analysis, Levels of development, Levels of organization, Neo- Piagetian theories of cognitive development, Shell

British sign language (BSL): the system of visual-gestural language developed in Britain. There are variants in many parts of the former British Commonwealth. Formalized types of sign language for the deaf probably grew out of written language in the 18th century, with deaf people using a finger as pen to trace words or ideas they were trying to communicate. See American sign language (ASL)

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bronchi: either of the two main airways or branches (or tubules) to the lungs that branch off the lower end of the trachea to connect with the lungs. They have an outer fibrous coat with irregular placed plates of hyaline membrane, and an inner coat consisting of smooth muscle and a mucous membrane of columnar epithelial cells. There is no gas exchange in this part of the respiratory system. See Alveoli, Broncopulmonary dysplasia, Epithelium, Smooth (or involuntary) muscle broncopulmonary dysplasia: one of the most frequent respiratory disorders in preterm infants due to the treatment of severe respiratory distress by means of artificial ventilation (and therefore a relatively new complication), and which can result in considerable damage of the lung tissue (in particular abnormal tissues in the bronchi of the lungs). See Bronchi, Dysplasia, Preterm infant, Respiratory distress syndrome (RDS) bullying: systematic harrassing, pestering or attacking of a child by another child or group of children. More generally, it amounts to repeated oppression that can be psychological or physical of a less powerful person by a more powerful person, a definition that would include adult as well (e.g., workplace bullying). There are, however, a number of different definitions of bullying, but they seem to share three things in common: it consists of deliberately hurtful behaviour (which would include malicious rumours or stories or exclusion from the social group), it occurs repeatedly over a period of time, and it is difficult for those being bullied to defend themselves. See Aggressive behavior, Conduct disorders, Fighting

C co-regulation: the idea that in face-to-face social interaction, social partners simultaneously and continuously adjust their thoughts, feelings and actions to those of their interlocutor. The concept of co-regulation implies that individuals are not autonomous in their social behavior. See Bi-directionality, Communication, Conversation, Interaction, Reciprocity cadherins: one of the so-called cell adhesion molecules CAMs), they are a family of functionally related cell surface glycoproteins (Ca2+-dependent CAMs), first identified in vertebrates, that play a role in differential calcium-dependent cell-to-cell adhesion. Attached to the cytoskeleton of a cell, they can occur transiently or permanently on the cell bodies of most vertebrate species at some point in their differentiation. They are divided into sub-classes E-, P-, and N-cadherins, each of which are distinct in immunological specificity and tissue distribution. These compounds have an important function in the construction of tissues and in morphogenesis more generally. See Cell adhesion molecules (CAMs), Cytoskeleton, Glycoproteins, Integrins, Morphogenesis, Mucins, Selectins caenorhabditis (C.) elegans (or nematode): a species of microscopic (1 mm), transparent round worm found in the soil and used for genetic studies as it has a small genome of only six chromosomes, about 3000 genes, few cell types and thus a relatively simple nervous system. It is ideally suited for research in developmental genetics as it only has a 16-hour period of embryogenesis in a petri dish. It was the first multicellular organism to have its genome sequenced, something that was achieved in 1998. See Chromosome, Developmental genetics, Embryogenesis, Genome Genomics, Human Genome Project (HGP)

Cajal-Retzius cells: originally identified by S. Ramon y Cajal (1832-1934) and Gustaf Retzius (1842-

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1919), they are neurons situated in the marginal zone of the human embryo that have radial ascending connections with pia mater (the innermost membrane enveloping the brain and spinal cord), and a horizontal axon plexus located in the deep marginal zone. Evident in mid- gestation in the human fetus, there is some controversy about their functions and developmental course. One reason is that Retzius cells appear to be distinct from those identified by Cajal and that they correspond more closely to what was previously taken to be human Cajal-Retzius cells. It is now thought that Retzius cells play a role in the migration, placement and inside-outside organization of the cortical plate neurons. Once they have served these functions, it is believed they disappear, perhaps through apoptosis. However, recent research has established that Retzius cells are transient, and restricted to the period of cortical migration. Cajal cells, in contrast, mature later in development, and may even persist into adult life. Whatever the case Cajal-Retzius cells (or perhaps just Retzius cells) represent a possible example of an ontogenetic adaptation and a qualitative regression in development. See Apoptosis, Cell migration, Cortical plate, Ontogenetic adaptation, Qualitative and quantitative regressions calcarine sulcus (or fissure): discovered and named by Thomas H. Huxley (1825-1895) in 1861 during his pursuit of the ‘hippocampus minor’ in non-human primates, it is a sulcus that begins under the posterior end of the corpus callosum and arches to the occipital pole. The visual cortex is arranged around this sulcus. See Corpus callosum, Sulcus, Visual cortex canalization: according to Conrad H. Waddington (1905-1975), this concept represents a general summary of a number of facts in genetics and embryology. Broadly speaking, it can be defined as the capacity of the epigenetic system to attain developmental end-states despite minor variations in initial conditions and conditions met during subsequent development (viz., genetic and environmental perturbations). The depth to which a developmental pathway is canalized or buffered is taken to represent the strength of its homeorhetic properties. See Constraint, Determination, Equifinality, Homeorhesis, Epigenetic landscape, Epigenetics canon of parsimony: generally considered to be a special case of Ockham’s razor in its application to animal or comparative psychology made by C. Lloyd Morgan (1852-1936) in his Introduction to comparative psychology (1894). Prior to Morgan, Wilhelm Wundt (1832-1920) put forward a similar idea in his Lectures on human and animal psychology (1863). The canon is summarized in the Introduction with the well-known sentence as follows: “In no case may we interpret an action as the outcome of the exercise of a higher psychical faculty, if it can be interpreted as the outcome of the exercise of one which stands lower in the psychological scale” (p. 53). Given this description, it is surprising that the canon was assumed to be a justification for the anti-mentalism of behaviorism during its dominant years in Psychology. As Robert H. Wozniak, and others, have pointed out, this assumption was misplaced. In effect, Morgan’s canon does not amount to a principle of parsimony as it does not eradicate mental processes or hold that the only focus of study should be observable behavior. Rather, it is an appeal to psychologists that they should know their own minds if they are to understand the conscious experience of other animals. Thus, it is not a denial of mental events in animals in the name of parsimony, but instead the opposite. More to the point, it was intended as a guide to psychologists as to how to use their own introspections in studying animal behavior within the broader context of a concern for mental evolution. In this respect, the canon emphasized the avoidance of imposing ‘higher’ mental functions on interpretations of animal behavior when ‘lower’ ones would suffice. See Comparative method, Ockham’s razor carboxyhemoglobin (CoHb): a derivative of hemoglobin, also known as carbon monoxide hemoglobin,

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it is a fairly stable union of carbon monoxide with hemoglobin instead of oxygen or carbon dioxide. It has a much higher affinity for hemoglobin than oxygen, and at high levels impairs the normal transport of oxygen by the blood. The normal value of CoHb in blood is 3%, but it can get as high as 15% in smokers. Levels change significantly, both in the mother and fetus during maternal smoking, and may lead to chronic intrauterine hypoxia and reduced birthweight. However, it is still not clear if the physiological effects of maternal smoking on fetal growth are due to decreased availability of oxygen as a consequence of the formation of COHb, or to the vasoconstrictive properties of nicotine. See Hemoglobin, Hypoxia, Intrauterine growth retardation (IUGR), Nicotine, Vasoconstriction carcinogen: a substance or agent that causes cancer, and which are often (but not necessarily) mutagens or teratogens. They cause cancer by altering DNA. With the exception of tobacco, what is sometimes not recognized by the general public is that almost all carcinogens consumed by humans are contained in plants, something that prevents plants from being eaten by animals. Bracken, for example, contains large amounts of carcinogens. See DNA, Environmental tobacco smoke (ETS), Mutagens, Teratogens cardiac muscle: involuntary striated muscle found only found in the wall of the heart, with other involuntary muscles being in general smooth. It has a longer refractory period than skeletal striated muscle elsewhere in the body, and a consequence does not fatigue. See Catecholamines, Smooth muscle, Striated (or striped or voluntary) muscle cardiovascular accidents (CVAs): a hemorrhage or thrombosis involving the arteries that supply the heart; a ‘heart attack’. Risk factors associated with CVAs include smoking, ‘bad’ cholesterol (LDL-cholesterol), but not ‘good’ cholesterol (HDL-cholesterol), and high blood pressure. See Cholesterol, Environmental tobacco smoke (ETS), Nicotine, Risk factor case-comparison design: a research design in which cases of a given disease or other condition are sampled for study. A comparison sample of persons not having the condition is also recruited, as far as possible from the same basic population. These samples are then compared on exposure to hypothesized risks for the condition. See Epidemiology, Odds ratio, Rate ratio, Risk factor catastrophe theory: devised originally by René F. Thom (1923-2002) to model mathematically Waddington’s epigenetic landscape. It is a theory of dynamical systems based on analogy with topographical form and dealing with instabilities in a limited sub-class of dynamical systems that can be described by potential functions. If a system consists of n variables, then one of its states can be represented by a region in this space. Such regions are subjected to topographical classifications (e.g., cusp catastrophe, see figure below) and, under particular circumstances, a sudden or catastrophic jump can take place from one state to a qualitatively different one as a consequence of changes in two or more control parameters. The theory has been used to model a number of psychological phenomena, but one of its drawbacks for modeling developmental processes is that it cannot yet deal with longitudinal data. See Analogy (as a trope), Bifurcation, Control parameter, Epigenetic landscape, Dynamical system, Dynamical systems approaches, Hysteresis, State (or phase) space, Synergetics

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A cusp model depicting developmental change in grasping. Smooth continuous change between two types of grasping is shown by the path from a to f, which does not pass through the bifurcation set. If the movement along this path was to stop opposite point e, then small differences between the combined values of the two control parameters could be attracted along the downward slope to widely different outcomes as this point is approached – one going along the pincer grasp surface, the other along that for the scissor grasp. A move from a to b, by altering ask demands at a particular competence level, leads to crossing the bifurcation set and therefore discontinuous change. Such a change may involve a hysteresis cycle (b->c->d->b) in which the two forms of grasping co-exist temporarily, but with no intermediate values. catching: grasping a moving object with one or two hands. See Prehension catecholamines: a group of hormones that act as neurotransmitters, which are mainly manufactured by the chromaffin cells (the secretory organelles) of the medulla of the adrenal glands and from the postganglionic fibers of the sympathetic nervous system. The most abundant catecholamines are three closely related chemical messengers: epinephrine (adrenaline), norepinephrine (noradrenaline) and dopamine, all of which are made from amino acid tyrosine, and thus are referred to as biologically active amines or monoamines. They are involved in preparing the body for the ‘fight-or-flight’ response. When released, the heart beats stronger and faster, blood pressure rises, more blood flows to the brain and muscles, the liver releases stores of energy as a sugar (glucose) that the body can readily use, the rate of breathing increases and airways widen, while digestive activity slows down. The result of these reactions is to direct more oxygen and fuel to the organs most active in responding to stress, mainly the brain, heart, and striated muscles. See Adrenal cortex, Adrenal gland, Adrenal medulla, Cardiac muscle, Dopamine, Epinephrine (or adrenaline), Hormones, Neurotransmitters, Norepinephrine (or noradrenaline), Sympathetic nervous system (SNS), Striated ((or striped or voluntary) muscle, Tyrosine category learning: the ability to group objects together that are perceptually dissimilar (e.g., different

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cats), and treat them as members of a single category. The ability to form categories has been shown to exist even in 3-month-old infants. However, the category structures of infants differ from those of adults. It is a crucial type of learning as it underlies all forms of cognitive activities, and occurs simultaneously along different dimensions and at different levels of abstraction [e.g., ‘brown dog’ can evoke the dimensions of the color category, the part category (e.g., tail) and the object category (e.g., animal) at various levels of abstraction (e.g., ‘dark brown’, ‘short tail’)]. Such learning has been a focus of adaptive computational models of categorization. See Computational models, Learning, Representation (mental) caudal: at the back or end of the longitudinal axis of the body. See Rostral causal determinism (or causalism): the doctrinal assertion of the causality principle. In general terms, it advocates the idea that every event is necessitated by antecedent events and conditions, together with the laws of nature. Pursued thoroughly enough, it has been held, then it will explain all phenomena and thus give rise to a Theory of Everything. See Cause (or causal factor), Causality (in philosophy), Laws of nature, Theory of Everything (ToE) causal pathway: the sequence of causes leading to the outcome of interest. In epidemiology and the design of clinical trials, the identification of causal pathways leading to pathology is a major objective. In studying development, normal or pathological, causal pathways can be more readily identified from retrospective studies than from longitudinal data gathered prospectively. Structural equation modeling is one technique that allows (complex) causal pathways to be traced. Problems with demarcating causal pathways involve confounding and the use surrogate endpoints. See Cause (or causal factor), Causality (in philosophy), Confound, Confounding variable, Diagnosis (or diacrisis), Risk mechanisms, Structural equation modeling (SEM), Surrogate endpoints causality (as a psychological phenomenon): perception of cause-effect relationships among objects. The roots of this interpretation of causality lie with David Hume (1711-1776) who argued that causality is not a logical relationship waiting to be discovered, but rather is based on inferences derived from experiencing a succession of events. With this contention, he shifted the study of causality from logic to psychology. See Causality (in philosophy) causality (in philosophy): covers three distinct meanings. To begin with, there is causation (the causal relationship between two things when the first is a necessary and/or sufficient condition the occurrence of the second), the causality principle (a statement of the law of causation in the form ‘The same cause always or invariably produces the same effect’), and causal determinism. Following Aristotle (384-322 BP) and his distinctions between efficient, final, formal and material causes, Francis Bacon (1561-1626) established that causality (i.e., Aristotle’s efficient causality) could be open to empirical investigation, which resulted in the separation of science from philosophy. By the beginning of the 19th century, such simple linear causality (viz., if A causes B, then there is a logical relationship to be discovered by understanding the essences of A and B) was being challenged by notions of multiple causation. In the 20th century, quantum mechanics added a probabilistic dimension to the study of causality. See Causal determinism, Causal pathway, Circular (or non-linear) causality, Determinism, Explanation, Laws of nature, Necessary and sufficient conditions, Proximate mechanisms (or causes), Quantum mechanics, Probabilistic epigenesis, Systemic causality, Ultimate mechanisms (or causes) cause (or causal factor): the agent that activates or brings about change in a behavior mechanism. See

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Behavior mechanism, Causal pathway, Causality (in philosophy), Control parameter cell: in biology, the structural and functional unit of all living organisms, which exist as independent units of life in bacteria and protozoans, and first described by Robert Hooke (1635-1703) in 1665 with the aid of a light microscope. In other living organisms, they form colonies or tissues. Each cell contains protoplasm differentiated into cytoplasm and a nucleus containing DNA. There are two main types of cells: prokaryotic cells as in bacteria and eukaryotic cells in which the nucleus is surrounded by a nuclear membrane and the cytoplasm is divided by membranes into connected cavities and separate compartments referred to as organelles (e.g., mitochondria and Golgi organs). See Cell theory. Cytoplasm, DNA, Eukaryote cell (or organism), Golgi apparatus (or complex or organ), Mitochondria, Nucleus (of a cell), Organelle, Prokaryote cell (or organism) cell adhesion molecules (CAMs): receptors on the neuronal membrane with a configuration having a specific attraction to outgrowing axons and thus leading to specific connectivity. Specifically, they are proteins that mediate cell-to-cell binding, and consist of five main classes: cadherins, immunoglobin (Ig) superfamily proteins, integrins, mucins, and selectins (see table below for further details about four of them). CAMs hold together or integrate components of tissue, are important for the functioning of migratory cells such as white blood cells, as well as during embryonic development and morphogenesis. Mutations in genes for CAMs can result in abnormal cell-to-cell interactions and tumor growth. Furthermore, they hold synapses together, and the regulation of synaptic cell adhesion is involved in learning and memory. When this form of adhesion becomes abnormally regulated, Alzheimer’s disease can be the consequence. See Adhesion molecules, Alzeheimer’s disease, Cadherins, Cell recognition molecules, Growth cone, Immunoglobin, Ligands, Morphogenesis, Mucins, Mutation (biology), Neural cell adhesion molecule (N-CAM), Selectins, Synapse

Family Ligand Interaction Cadherins Cadherins Homophilic

Ig superfamily proteins Integrins Heterophilic Ig superfamily proteins Homophilic Integrins Extracellular matrix Heterophilic Ig superfamily proteins Hetrophilic Selectins Carbohydrates Hetrophilic

Main classes of cell adhesion molecules. Homophilic interaction: adhesion between two copies of the same adhesion molecule. Heterophilic interaction: binding between an adhesion protein and some other molecule cell assemblies: a group of neurons that act together in processing a certain task. One neuron can be part of several cell assemblies. Donald O. Hebb (1949), in his book The organization of behavior: A neuropsychological theory, introduced the notion of cell assemblies into psychology. According to him, stimuli, objects, but also more abstract psychological entities (e.g., concepts, ideas, memory) are represented in the brain by simultaneous activation of groups of neurons he referred to as cell assemblies. At the root of a definition of a cell assembly is connectivity (i.e., cells forming an assembly are connected by relatively numerous and/or strong mutual excitatory synapses). Moreover, if a sufficient number of cells in an assembly are stimulated, all cells in it tend to become co-activated. In his theory of cell assemblies, Hebb postulated specifically that synapses are strengthened when both connected

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cells are activated simultaneously within a certain time window. This learning mechanism is now referred to as the `Hebbian learning rule’. See Hebbian learning, Neuron, Synapse cell death: programmed cell death or apotosis is the patterned elimination of specific cells or tissues that occurs as a normal process during early development. It is particularly evident during prenatal development of the central nervous system. See Apotosis (or apoptosis), Synapse elimination cell locomotion: the ways in which cells move differ between eukaryotes and prokaryotes. For eukaryotes, most mechanisms seem to involve protein tubules or filaments sliding past one another and generating force. However, how such force is generated is not well understood, but adhesion molecules including integrins are involved. See Adhesion molecules, Axon pathway selection, Eukaryote cell (or organism), Integrins, Myosin, Prokaryote cell (or organism)

cell migration: during early development, neurons migrate along a short and direct route, using a transient population of radial glial cells as a sort scaffolding. Later, however, as the cerebral cortex begins to fold, the route becomes longer and more complex, the later migrating neurons assuming positions external or more superficial to those that arrived earlier. Thus, layer 2 neurons are generated and migrate later than layers 3, 4, 5 and 6. The deepest layers are the first to develop first, which results in an ‘inside-out, outside-last’ pattern of migration. All neurons of ‘higher’ vertebrate CNS are born in one place and migrate to another. In the spinal cord and parts of the brain stem, neurons are born near the ventricular surface, and then migrate in a radial, or vertical, direction away from this surface. However, they stop short of the outer pial surface and differentiate in this position. The outermost zone remains free of neuron cell bodies, and instead becomes populated by axons. Consequently, in the adult spinal cord and much of the brain stem, gray matter is inside and white matter is outside. The forebrain has three basic patterns of migration: • some neurons migrate vertically and stop short of the pial surface, just as in the spinal cord. They differentiate in this deep position to form most of the thalamus, hypothalamus, and limbic parts of the forebrain. • other neurons migrate vertically, but do not stop short as they migrate all the way out to the pial surface, where they form a layer of cells referred to as the cortical plate due to its location at the brain surface. The hippocampus begins as a simple cortical plate with one layer of cells, and never adds additional cellular layers (even though it continues to generate neurons through the life span). The cerebral isocortex begins development like the hippocampus. However, in the isocortex, there are several waves of later migrations, which travel vertically past the first arrivals, and thereby creating a cortex that has not one but multiple layers of neurons. • still other neurons leave the ventricular surface, but continue to divide. Their migrations before and after their ‘birthdays’ are usually horizontal or tangential rather than radial. These cells form the caudate nucleus, the putamen (both in the basal ganglia), the pulvinar of the thalamus, and the horizontally connecting cells in the isocortex. Abnormalities in neuronal migration are linked to a number of developmental disorders such as lissencephaly and those concerning the control of movement (e.g., cerebral palsy). Both dyslexia and schizophrenia have been ascribed to more subtle abnormalities in migration and in the development of synaptic connections. The molecular or genetic bases for these abnormalities are being revealed at an increasing rate using techniques like forward genetics in mice. For example two genes, FLN1 and ARFGEF2, are necessary for migration to start, and if they are mutated they never leave the proliferating ventricular zone. Another example is reelin, that normally arrests neurons in their appropriate places, but if mutated results in abnormal forms of locomotion among other

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things. In fact, it seems that there are a range of genes responsible for starting, maintaining and completing migration. See Basal ganglia (development), Brain stem, Cerebellum (development), Cerebral cortex (development), Cerebral cortex (disorders), Cerebral palsy, Dyslexia, Forward genetics, Glial cells, Gray matter, Hippocampus, Hypothalamus, Isocortex, Lissencephaly, Plial surface, Radial glia cells, Reelin, Spinal cord, Thalamus, White matter cell recognition molecules: particular proteins or other complex molecules generated by one cell type that another cell type has receptors for and can ‘recognize’ (i.e., receptor uptake of these molecules causes some change in the cell’s physiology, usually by genetic instruction). They mediate cell-cell and cell-extracellular matrix interactions. It appears that are a very large number of genes in the vertebrate genome that encodes for these molecules, which might be an outcome of increasingly more complex cellular interactions being selected for in the evolution of ‘higher’ metazoans. See Cell, Cell adhesion molecules (CAMs), Metazoan, Protein cell theory: in its modern form, the theory that all cells come from previously existing cells and that they are the fundamental functional units of all living organisms. Considered to be one of the most important theories in biology, it was originally proposed by Matthias Schleiden (1804-1881) in 1838 and again the following year by Theodor Schwann (1810-1882), it became known as the Schleiden-Schwann cell theory. Their theory proved to be untenable, largely because they claimed that cell generation started with a process of ‘crystallization’ within the intracellular substance followed by progressive enlargement, a claim refuted by others such as Rudolf Virchow (1821-1905) who pointed out that every cell comes from a pre-existing cell. Subsequently, there were problems in extending cell theory to nerve cells because at the time they were difficult to reconstruct. However, this was eventually achieved with the appearance of the neuron doctrine. See Cell, Neuron, Neuron doctrine center of gravity: a fixed point on a rigid body through which the resultant force of gravity always passes, regardless of the position of the body. In a uniform gravitational field, it is identical to the center of mass. Thus, for practical purposes, the center of gravity and center of mass coincide. In strict physical terms, however, there is an infinitesimal difference between the two. For the human body, the center of gravity is not at a fixed anatomical point, but its location varies with the position of the body segments. See Center of mass, Gravitational field, Inertia, Moment of inertia (I) center of mass: the point at which the mass of a rigid body can be considered to be concentrated. More technically, it is the point from which the sum of the moments of inertia of all parts of the body is zero. The center of mass is not always located in the body (see figure below) See Center of gravity, Inertia, Mass, Moment of inertia (I)

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The location of the whole body center of mass is dependent on posture. A: center of mass when standing upright is inside the body. B: center of mass when bending over is outside the body central coherence: the ability to integrate information into a gestalt (a perceptual structure possessing qualities that go beyond its constituent elements or parts, and that cannot be described solely in terms of its parts), or to build up a global picture. This particular ability appears to be a particular strength with those individuals diagnosed as autistic (e.g., as assessed by performance on the Embedded Figures test). See Autism, Embedded Figures test (EFT), Gestalt good form central dogma of molecular biology: a term coined by Francis H.C. Crick (1916-2004) in 1958, it states the idea that genetic ‘information’ flows in only one direction from DNA -> RNA -> protein. Put another way, it holds that DNA makes (or transcribes) RNA makes (or translates) proteins that in turn facilitate the previous two steps as well as the replication of DNA (see figure below). Accordingly, the flow can now be given as DNA -> DNA -> RNA -> protein. Following the discovery of reverse transciptase (RT) in retroviruses, the dogma was extended to RNA -> DNA. RT is an HIV specified enzyme essential for the replication of the virus. This enzyme is unique to HIV-like viruses and converts viral RNA into DNA, so allowing the HIV genome to be inserted into the cell's DNA. See DNA, DNA double helix, Enzyme, Modern synthesis, Molecular biology, Protein, Retrovirus, RNA, Theory of the germ plasm

Schematic summary of the central dogma of biology central nervous system (CNS): that part of the nervous system in vertebrates derived from the neural tube consisting of the brain (prosencephalon, mesencephalon, rhombencephalon) and cerebral ganglia, together with the retina (sometimes considered to be part of the peripheral system), spinal cord, and meninges. Anything else is considered to be the peripheral nervous system. It consists of two regions: gray matter and white matter. See Autonomic nervous system (ANS), Brain (or encephalon), Diencephalon, Ganglia, Gray matter, Neural tube,

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Mesencephalon, Peripheral nervous system, Peripheral nervous system (PNS), Prosencephalon, Retina, Rhombocephalon, Telencephalon, Spinal cord, White matter central pattern generator (CPG): a network of spontaneously active interneurons that emit modulated rhythmical activity. Those situated in the spinal cord are implicated in the coordination rhythmical activities such as locomotion. Some of these neurons are excitatory and others inhibitory. Thus, in the case of locomotion, when the agonist extensor muscles are activated, the antagonist flexors are inhibited. On completion of the extensor phase, it is inhibited and the flexors activated, with the cycle of excitation-inhibition repeating itself. There are problems with this theory that still have to be resolved satisfactorily (e.g., the mechanisms by which sensory input adjusts the output of the network to changing environmental circumstances and whether there are a variety of CPGs governing the different muscle groupings involved in rhythmical movements like locomotion, chewing and respiration). See Agonist muscle, Antagonist muscle, Coordination, Gait, Interneurons, Locomotion, Movement coordination, Spinal cord, Spontaneous movements centrifugal/centripetal: directed from center/directed to center. A centrifugal or efferent nerve fiber transmits impulses from centers in the nervous system to the parts to which the nerves are distributed, thereby exciting muscle contractions or influencing the processes of nutrition, growth, and secretion. A centrifugal force, a form of inertia, tends to move objects away from the center in a system undergoing circular motion (e.g., in throwing the driver of a car against the door when negotiating a sharp bend). A centripetal or afferent nerve fiber or impulse is one originating outside and passing toward the central nervous system. A centripetal force is one whose direction is towards a center. It acts on a body in a curvilinear motion that is directed toward the center of curvature, and which is necessary for a body to move in circular motion (e.g., as in ice skating). See Axon, Force, Inertia, Neuron centromere: part of a chromosome containing no genes, but controlling chromosome activity, located at the point lying on the equator of the spindle at metaphase during mitosis and which divides at the anaphase. See Anaphase, Chromatid, Chromosome, Metaphase, Mitosis, Spindle cerebellar cortex: the outer layer of the cerebellum (also known as the corticocerebellum, molecular layer and neocerebellum) with a surface area of 50,000 cm2 in the adult human, mainly consisting of parallel fibers and cerebellar interneurons. See Basket cells, Cerebellum (anatomy), Interneurons, Parallel fibers cerebellum (anatomy): first identified by Herophilus (355-280 BP), the father of anatomy (who also identified the cerebrum and ventricles in humans), it is commonly referred to as the ‘small brain’, and as the head ganglion of the proprioceptive system by Sherrington. The cerebellum is a major structure of the metencephalon (hindbrain), lying above and posterior to the medulla oblongata and the pons, that occupies most of the posterior cranial fossa. Consists of outer layer of gray matter about 2mm thick (the cerebellar cortex) that overlies a central core of white matter. It is connected to the brain stem by three cerebellar penducles or attachments (see figure below): the inferior cerebellar penducle (or restiform body) containing afferent fibers, the middle cerebellar penducle (or brachium pontis) that also contains afferent fibers, and the superior cerebellar penducle that carries efferent fibers from the deep cerebellar nuclei to the tegementum (dorsal part of the midbrain).

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The three cerebellar penducles. The inferior peduncle receives information from the spiniocerebellar tract, the inferior olivary nucleus, and the reticular formation, and send outputs to the thalamus, reticular formation and vestibular nuclei. The latter convey information abou the spatial orientation the head, joints and muscles. The middle penduncle has inputs from the pontine nucleus and relays them to neocerebellum, this being the main pathway from the cerebellum to the cerbellar cortex. The superior peduncle, the major ouput of the cerebellum, crosses before it gets to the thalamus, and thus influences ipsilateral movements.

In adult mammals, it makes up about 12% of the total brain mass, and in adult humans it weighs about 142 grams, contains about 70% of the neurons in the brain, and has three- quarters the surface area of the cerebral cortex even though it is much smaller. The latter achieved through the cerebellar cortex being corrugated by many many parallel transverse convolutions or gyri called folia, which are separated from one another by fissures (cf., sulci in the cerebral cortex). Together the folia and fissures increase the surface of the cerebellar cortex, while at the same time giving it a walnut-like appearance. Three transverse divisions provide one perspective on the gross anatomy of the cerebellum (the other being longitudinal divisions) to reveal three lobes, each having distinct functions. One (the flocclunodular/posterior lobe) is the archicerebellum (or vestibulocerebellum), phylogentically the oldest part of the cerebellum and the first to appear in development,that receives input from the vestibular nerve and the medial and lateral vestibular nuclei. This part of the cerebellum plays a role in the modulation of muscle power and postural control of the antigravity muscles more generally through its influences on the trunk muscles. It also has a role in spatial orientation. Another (the anterior lobe) is the palaeocerebellum (or spinocerebellum) formed by the vermis and anterior

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parts of the cerebellar hemispheres, which receives inputs from the vestibular system. It too plays an important part in the regulation of muscle power and posture as it receives proprioceptive inputs from the limbs. A third division (the posterior/middle lobe) is the neocerebellum (or corticocerebellum or pontocerebellum), phylogentically the newest part of the cerebellum, forming the most of the cerebellar hemispheres and part of the vermis and that is the recipient of inputs from the auditory, cutaneous and visual systems. Essential in the coordination of discrete voluntary movements initiated by the cerebral cortex, it is responsible for braking or checking such movements (e.g., reaching). The cortex of the cerebellum is organized into three layers (molecular, Purkinje cell, granular), containing three fibers (climbing,mossy, parallel), and five intrinsic neurons (granule, Golgi type II, Purkinje, parallel, interneurons consisting of basket and stellate cells). The intrinsic circuitry of the cortex involving these neurons,the excitatory and inhibitory inputs to the Purkinje cells, and the inputs and outputs of the cerebellum are illustrated in the following figures.

A. Intrinsic circuitry of the cerebellum. The climbing fibers (CF) and the mossy fibers (MF) form axondendritic synapses, the former with Purkinje cell (PC) dendrites, the latter with granule cells (GC), and both with the deep cerebellar nuclei (DCN). Both provide excitatory inputs ( ) to the Purkinje cells whose output inhibits the DCN. The inhibitory inputs ( ) consist of the basket cells (BC), stellate cells (not shown) and the Golgi II cells (GC).

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B. Schematic summary of the excitatory +) and inhibitory (-) inputs to the Purkinje cells.

C. Inputs to the cerebellum. The inferior olive is situated in the lower part of the medulla oblongata in the brain stem. AC: archicerebellum. Cf: climbing fibers. Mf: mossy fibers, NC: neocerebellum. PC: palaeocerebellum.

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D. Outputs from the cerebellum. The deep cerebellar nuclei in the brain stem consist of four major nuclei: the dendate nucleus (the largest) and three nuclei in the interposed nuclei, namely, the fastigial nucleus, globose nucleus, and emboloform nucleus. Note that both cerebellar inputs and ouputs cross the body midline. However, the cerebellum controls movements ipsilaterally (i.e., on the same side of the body). This is because outputs from the motor cortex cross back over the midline, thus making any influence from the cerebellum ipsilaterally. This phenomenon is known as ‘double crossing’.

The cerebellum is perhaps the mostly clearer ordered and organized brain structure in the central nervous system. It has been seen by some as a natural ‘work of art’, comparable to the finest pieces of architecture ever constructed by humans. It is not surprising, therefore, that much research has been carried out on its structure and function relative, for example, to the basal ganglia. Much of inherent beauty was revealed, or at least brought to public attention, by John Eccles (1903-1997). See Basal ganglia (anatomy), Basket cells, Cerebellar cortex, Cerebellum and basal ganglia, Climbing fibers, Deep cerebellar nuclei, Extrapyramidal system, Golgi type II cells, Granular layer, Granule cells, Granular layer, Inferior olive nucleus, Mesencephalic reticular activating system, Metabolism, Molecular layer, Mossy fibers, Motor cortex, Motor learning, Parallel fibers, Purkinje cell layer, Purkinje cells, Stellate cells, Ventrolateral thalamus, Vestibular nuclei cerebellum and basal ganglia: both share a number of similarities in terms of structure (i.e., hodology) and function. With regard to structure, both have projections to and back from the premotor cortex via the thalamus, and both function together to process information from the association cortex in the service of organizing and executing movements (see figure below). The differences include the fact that while the basal ganglia receive inputs from the whole of the cerebral cortex, the cerebellum has no direct inputs. Moreover, outputs from the cerebellum go to the premotor and motor cortices, with the basal ganglia projecting to the frontal cortex as well. While both structures work in combination functionally, they have been accorded different roles in the control of movement: the basal ganglia are thought to participate in the preparatory control of movements and with the generation of ramp movements, while the cerebellum directly regulates movements into a unitary action through taking account feedback from the periphery (e.g., muscle spindles) and by means of error correction of motor cortex via a negative feedback loop involving the spinocerebellum. Finally, there is increasing evidence that both structures are implicated in non-motor functions. See Basal ganglia (anatomy), Cerebellum (anatomy), Frontal cortex, Hodology, Motor cortex, Premotor cortex, Thalamus

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Cerebellum and basal ganglia work in tandem in the control of movements. Both process information from the sensory association cortex, and use this information to prepare a movement appropriate to a task (e.g., writing a legible signature at the right speed and size). This information then serves as commands to the premotor and motor cortices (and also to sub-cortical areas). The cortical areas execute the movement and inform the spinocerebellum of ongoing commands, which in turn corrects for any errors in movement execution and compensates for them. From Allen, G. I., Tsukahara, N. (1974). Cerebrocerebellar communication systems. Physiological Review, 54: 957-1006. cerebellum (development): the cerebellum, relative to other brain structures, has a protracted developmental course, such that a considerable portion takes place postnatally. Its origins and those of its associated nuclei begin in week 7 of the embryonic period and its neurogenesis is complete some 6 months after birth. It starts in the embryonic period with neuroblasts located at the border of the fourth ventricle whose walls spread out laterally to form the rhombic lip at 5- 6 weeks. This transient diamond-shaped cavity, which appears as a consequence of the pontine flexure (a bend in the long axis of the brain stem that subsequently disappears), gives rise to the cerebellum (a number of brain stem nuclei) that will eventually cover the fourth ventricle as it grows out more caudally than rostrally. More specifically, it is from a considerable increase in the size of the anterior rhombic lip that the cerebellum is formed (the posterior rhombic lip giving rise to the inferior olivary nucleus and its lateral corners to cochlear nuclei). The beginning of cerebellar development is also marked by the separation of the cortical plate from the intermediate zone. Neuroblasts remaining in this zone become the deep cerebellar nuclei, while those that migrate out from it become the Purkinje cells and Golgi type II inhibitory interneurons. The external granular layer is formed from the sub-ventricular zone at the edge of the rhombic lip. The axons of this layer, the last to develop in the cerebellum, grow parallel to each other, and thus are termed the parallel fibers. At the same time, the granule cell bodies migrate inward along radial glial cells past the Purkinje cells to form the internal granular layer, and the Purkinje cell dendrites grow into the molecular layer where they then begin to branch profusely. Thus, unlike the cerebral cortex, the cerebellum undergoes an ‘inside and outside’

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pattern of migration (i.e., the granule cells migrate inward, possibly with the aid of pre-existing radial glial cells that act as guide wires as in the cerebral cortex, to form an new internal granular layer, and the Purkinje cells migrate radially outward). As for the Purkinje cells, each one synapses with the largest possible number of parallel fibers. The external granular layer is also the birthplace of the basket and stellate inhibitory interneurons, but which remain in the molecular layer. Neurons in the external granular layer continue cell division longer than most others in the developing brain. This layer still contains dividing cells at birth, with division (and proliferation) continuing until about 6 months after birth in the human. Thus, the external granule layer is the last to develop in the cerebellum, and as such has consequences for the development of movement coordination. PET scans, however, have revealed that cerebral glucose metabolism is higher in the cerebellum (as well as in sensorimotor cortex, thalamus and brain stem) compared to the basal ganglia and cerebral cortex at 5 weeks after birth, something that coincides quite well with the two-to-three month transformation resulting the first appearance of behavior that appears to be under voluntary control. Furthermore, the later- occurring external granule cells are vulnerable not only to the effects of intrauterine growth retardation, but also to medulloblastoma, a malignant tumor occurring during this age range. If it remains restricted to the cerebellum, it may be possible to remove the tumor. This operation, however, entails ablating most of the cerebellum, and while the children who have had it can develop locomotion and postural control normally, they lose the ability for the motor learning required to acquire novel skills such riding a bicycle or skating. Other developmental disorders such as when the Purkinje cells are perturbated in their migration, result in a marked reduction of the number of granule cells that are essential in forming the regionalization of the cerebellum. The converse is for some reason not the case. Postnatally, however, if the granular cell layer is adversely affected (e.g., through oxygen deprivation to which it is susceptible), then the Purkinje cells form dysmorpholgies such as disoriented and stunted dendritic spines. Thus, the interaction of the migrating Purkinje cells and granule cells is crucial to the formation of parallel fibers, the differentiation of the Purkinje cell dendritic trees, for synaptic contacts between them, and consequently for functional development more generally. See Basal ganglia (development), Brain (neuro-) imaging, Brain stem, Cell migration, Cerebellum (anatomy), Cerebral cortex (development), Coordination, Cortical plate, Dendrite, Intrauterine growth retardation (IUGR), Medulloblastoma, Motor learning, Movement coordination, Neuroblasts, Neurogenesis, Purkinje cells, Radial glia cells, Rhombic lip cerebellum (disorders): disorders due to lesions to the cerebellum can arise for a number of reasons (e.g., toxins such as ethanol, anticonvulsants), cerebellar degeneration resulting from autoimmune disorders or inherited, structural lesions such as strokes and tumors or caused by trauma). Such lesions lead to limb disorders on the same side of the lesion due to the phenomenon of double crossing. Unlike damage to the basal ganglia, they do not lead to paralysis of involuntary movements. Neocerebellar lesions result in a number of disorders (or signs) that are not mutually exclusive (see table below). In general, they give rise to release phenomena such that other structures (e.g., lateral ventral thalamus) are released from the inhibitory influences of the cerebellum. The neocerebellum is particularly sensitive to oxygen deprivation during the last trimester of pregnancy, and in this respect fetuses suffering from IUGR may have an increased risk of acquiring cerebellar disorders. Archicerebellar lesions are associated with truncal axatia, but without hypotonia or tremor. The effects of lesions to the palaeocerebellum are not clear in humans, but there is a tendency to show signs of degeneration in alcoholic patients, leading more to effects on the control and coordination of the legs than the arms. In general, children with cerebellar lesions tend to show good recovery of functions, perhaps because the cerebellum is still developing for some time after birth, or because of some of its functions are taken over by other brain structures such as the basal

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ganglia. See Ataxia, Basal ganglia (disorders), Brain damage studies, Cerebellum (anatomy), Cerebellum and basal ganglia, Cerebellum (functions), Cerebellum (development), Intrauterine growth retardation (IUGR)

Sign Description Hypotonia Diminution of tendon reflexes and resistance to passive (imposed) movements, delay in response to imposed movements such that there is an inability to stop limb rapidly (‘lack of check’ sign), muscles weak and flabby and tire easily (asthenia) Ataxia Inability to control and coordinate voluntary movements in the fingers and hands, arms or legs, and eyes, and during speech or swallowing Asynergia Breakdown of multi-joint movements into component parts (movement decomposition) resulting in a puppet-like performance (e.g., in face-to-nose test in which the raised hand is brought to contact the nose) Dysmetria Overshooting or past pointing the endposition aimed at with a movement (e.g., in the face-to-nose test) Dysdiadochokinesia Irregular alternating movements (e.g., in pronation-supination of hands) Action/intention tremor Tremulous movement execution, particularly at its terminus (terminal tremor), but not present during rest Ataxic gait Uncoordinated gait characterized by a wide support base, the feet pointing outward and irregular steps and rhythm. Sometimes referred to as a ‘drunken man’ gait Dysarthia Slow, slurred speech arising from inadequate control of facial muscles Scanning speech Staccato-like speech with pauses in the wrong places

Signs associated with lesions to the neocerebellum cerebellum (functions): It is generally considered to be involved in a feedback circuit governing the activity of the extrapyramidal motor system. As an important part of the motor system, it controls muscle tone and involuntary movements and provides coordination and integration of movements, as well as other timing functions in behavior. Damage to the cerebellum impairs motor learning. Beyond this well-known depiction of the role of the cerebellum in motor control, recent research is revealing that it has a host of 'non-motor' functions. One derives from PET studies using the so-called generation task [i.e., where a verb (e.g., 'eat') has to be matched with an appropriate noun (e.g., 'apple')] with or without speech. Such studies have shown that the right cerebellum becomes active when the task is performed without speech. Accordingly, the cerebellum might guide the conscious selection of appropriate verbs in ways similar to guiding movements. Consequently, this sort of finding might implicate the right cerebellum in reading abilities. Furthermore, neurological studies with brain-damaged patients and neuroimaging with healthy individuals have implicated the cerebellum in a variety of sensory and cognitive tasks, as well as in certain motor (or sensory-motor) tasks. In particular, these data suggest cerebellar involvement in: the generation of words according to a semantic rule, timing of events, solving perceptual and spatial reasoning problems, mental rotation, visual information processing, cutaneous and tactile discrimination, kinesthetic sensation, mental imagery, and working memory, among other processes (e.g., sensory process involved in

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thirst). See Brain (neuro-imaging), Cerebellum (anatomy), Cerebellum (development), Cerebellum (disorders), Coordination, Extrapyramidal system, Motor learning, Movement coordination, Muscle tone, Working memory cerebral cortex (or pallium): the six-layered, 1.4 to 4 mm convoluted sheet or mantle of neural tissue (unmyelinated neurons or gray matter), supported by deep white matter and separated by a prominent, longitudinal central fissure dividing it into in two hemispheres, that dominates the outside view of the human brain and forming the cerebrum. In fact, over 60% of the primate is ‘buried’ from view. Originally identified by Brodmann in 1909, the six layers or lamina (see figure below). From the most superior (outside) to most inferior (inside) they are: the molecular (I) layer (containing neuroglial cells and receiving nerve fibers from deeper areas), the external (II) granular layer (densely packed with small granular, stellate and pyramidal cells), the external, or medial pyramidal, (III) layer (with pyramidal cells arranged in rows) the internal granular (IV) layer (thinner, but has same cells as the external granular layer, especially small closely packed stellate cells), and which is the primary region of input to the cortex from the periphery, especially the thalamus), the ganglionic (V) layer (a mixture of small granular cells, large pyradmidal cells that have output to the brainstem and spinal cord, and cells of some association fibers, which form the bands of Baillarger and Bechterew), the fusiform, or multiform, (VI) layer (lots of different neuron types of neurons whose dendrites ascend to the internal granular layer, and whose axons enter the white matter in projecting to the thalamus, but whose function is not clearly understood).

The six layers or lamina of the cerebral cortex.

Based on gross morphology, the cerebral cortex is divided into four lobes (each sometimes being referred to as a cortex): frontal lobes, parietal lobes, temporal lobe and occipital lobe (see figure below).

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The four lobes of the cerebral cortex. The central sulcus divides the frontal lobe from the other three lobes, and the lateral sulcus the parietal lobe from the temporal lobe. Figure reproduced by kind permission of Patrick McCafferty, California State University, Chico.

Sometimes the limbic system or lobe is treated as a fifth lobe in some classification. Based on the work of 19th and early 20th century histologists, a number of architectonic areas have been identified in the cortex that vary from one of these pioneers to another to the other, examples of which are as follows: • Korbinian Brodmann (1868-1918): 49 areas • Cécile Vogt (1875-1962) & Oskar Vogt (1870-1959): >200 areas • Constantin von Economo (1876-1931): 109 areas • Walter Campbell (1868-1937): 20 areas Brodmann’s areal classification or map of ‘postcodes’ tends to be the mostly widely used, which he arrived at sequentially (1 to 49) by electrical probing the cortices of epileptic patients during surgery and noting the behavioral events that resulted form the stimulation (see figure below).

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Some of Brodmann’s cortical areas. Figure reproduced by kind permission of Patrick McCafferty, California State University, Chico.

Most of the white matter of the cerebral cortex is made up cortico-cortical connections that are far in excess of the cortico-thalamic and thalmo-cortical connections to the brain stem and spinal cord. Adjacent gyri are connected by U-shaped fibers that run through the white matter. The more distant these connections, the more deeper they are located in the white matter. In the adult human, the total surface area of the cerebral cortex is about 2500 cm2, with a thickness varying between 1.5 to 4.5 mm. In the mammalian cortex, the convolutions arise from gyri and grooves referred to as sulci. These allow more surface area for a greater number of neurons while keeping the volume of the brain compact enough to fit inside the cranium. A more literary term than isocortex or neocortex, which refer to the same structure. See Brain (or encephalon), Cortical columns, Corpus callosum, Cortical lobes, Gray matter, Gyrus, Isocortex, Limbic system, Neocortex, Sulcus, Thalamus, White matter cerebral cortex (disorders): common examples are aphasia, apraxia, agnosia and one-side (or contralateral) neglect. One of the most widely studied disorders in cortical structure is lissencephaly resulting from the arrest in migration of all cortical neurons before they reach their normal expected destinations. See Agnosia, Aphasia, Apraxia, Cell migration, Lissencephaly cerebral cortex (development): the first neurons that go to form the human cerebral cortex are generated during the first half of gestation in the proliferative ventricular zone close to the cavity of the cerebral ventricle. They undergo a complicated form of migration, termed the ‘inside-out’ pattern, in which the later born neuroblasts travel past those born earlier to the more superficial layers. After the crucial transition in cortical differentiation from mitotically active neuroblasts to postmitotic young neurons, the cortex begins to form radially-organized columns, the basic functional units for sensory processing and motor output that have been most studied in terms of touch-modality columns in the somatosensory cortex and orientation and ocular dominance columns in the primary visual cortex. Evidence of columnar organization has been found in

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other cortical areas (e.g., primary auditory cortex, primary motor cortex), with the suggestion that it is also a characteristic of non-cortical areas (e.g., the brain stem and superior colliculus). It is thought that the expansion of the cortex that becomes strikingly evident some 4 months after conception is due to increases in the number of columns rather than from increases in the sizes of individual columns. Furthermore, it is hypothesized that columnar development is driven by a process of activity-dependent self-organization. Age-related morphometric studies of the cerebral cortex in humans show developmental changes continuing into adolescence, especially with regard to the frontal cortex. Interneuronal connectivity develops rapidly during infancy and early childhood, with excess synaptic connections being eliminated. See Activity- dependent organization, Cell migration, Cerebral cortex (anatomy), Frontal cortex, MRI morphometry, Neuroblasts, Proliferative ventricular zone, Self-organization, Synapse elimination cerebral cortex (functions): broadly speaking, the cerebral cortex is responsible for so-called ‘higher- order’ functions such as thought, voluntary movements, reasoning and perception. One way of accounting for its functions is by means of considering those ascribed to the four lobes: • frontal lobe: associated with reasoning, planning, parts of speech, voluntary movement, emotions and problem solving. Specific parts of the frontal lobe communicate with areas of the parietal lobe concerned with 3-D perception. • occipital lobe: associated with ‘higher-order’ visual perception (e.g., depth perception, detection of edges and borders, object recognition).It has two output pathways: the dorsal stream concerned with the visual location of objects and the ventral stream with the identification of objects. • parietal lobe: associated with movement, orientation, recognition, perception of somatosensory information, and the formation of 3-D representations, in addition to processing information contained in the dorsal stream. • temporal lobe: associated with the perception and recognition of auditory stimuli, memory and speech. Information from the dorsal stream is fed by the temporal lobe to the hippocampus and associated structures. A long-standing issue about the functions of the cerebral cortex relates to the degree to which they are deemed to be localized in discrete areas of this structure. At one extreme, intimations of which can be detected in Greek antiquity with Hippocrates (460- 377 BP), Plato (427-347 BP), and Galen (129-210), but really stemming from the first half of the 19th century with the phrenology of Franz Josef Gall (1758-1828) and later subjected to case- study observations by Pierre Paul Broca (1824-1880) and to experimental verification by the likes of Gustav Theodor Fritsch (1838-1927) and Eduard Hitzig (1838-1907), support was garnered for the functional localization hypothesis. One who came to a more intermediate standpoint was Marie-Jean-Pierre Flourens (1794-1867), an opponent of phrenology, who found evidence for localization of functions in sub-cortical structures such as the cerebellum, but concluded that mental functions were dispersed throughout the whole cerebrum. Without doubt, the most convincing evidence for the hypothesis in the 19th century came with the work of David Ferrier (1843-1928) and his book Functions of the brain (1876), a student of Alexander Bain (1818-1903) who was influenced by the writings of John Hughlings Jackson (1835-1911), While this hypothesis of exact cerebral localization was challenged by the view of equipotentiality (viz., cortical functions are distributed throughout areas of the cerebral cortex that constitute uniform fields) stressed by Karl Spencer Lashley (1890-1958), it has in recent years gained the ascendancy with the incursion of the notion of modularity into cognitive neuroscience and the increasing sophistication of functional imaging techniques. See Brain (neuro-) imaging, Cerebral cortex (or pallium), Cortical lobes, Dorsal stream, Modularity, Ventral stream

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cerebral (or intracerebral) hemorrhage: also called a hemorrhagic stroke, it is a hemorrhage or bleeding into the substance of the cerebrum, usually in one hemisphere and in the region of the internal capsule through the rupture of the lenticulostriate artery (one of the branches of the middle artery that supply structures in the basal ganglia where most hemorrhages due to ruptured microaneurysms occur). It can happen as a consequence of very preterm delivery, and constitutes a risk for cerebral palsy. See Basal ganglia (anatomy), Cerebral palsy, Internal capsule, Very (or extremely) preterm birth cerebral palsy: the cerebral palsies are a heterogenous collection of motor disorders, best defined as a group of non-progressive, but often changing, motor impairment syndromes secondary to lesions or abnormalities of the brain arising in the early stages of its development. What is ‘non- progressive’ (i.e., permanent) is the cerebral lesion, while its functional manifestations change with age as the central nervous system and the muscoloskeletal system develop. Most classifications of cerebral palsy distinguish between spasticity and two other prominent forms of the disorder (viz., ataxia, dyskinesia). There are various forms of treatment for cerebral palsy ranging, for example, from surgery to altering tendon lengths (tenotomy) and performing dorsal rhitozomies to the administration of pharmacological agents such as botox to physical therapy. See Ataxia, Athetoid (or athetotiform) movements, Botulinus (or botulinum or botox), Cell migration, Cerebellum (disorders), Cerebral (or intracerebral) hemorrhage, Clonus, Developmental disorders, Developmental risks, Dorsal rhizotomy, Dyskinesia, Handicap, Impairment, Musculoskeletal system, Spastic diplegia, Spastic hemiplegia, Spastic quadraplegia, Spasticity cerebrospinal fluid (CSF): clear, colorless fluid that fills the neural tube and later circulates through the four ventricles of the brain, within which it is secreted and then propelled by ependymal cells that line the walls of the ventricles. The fluid is absorbed into the bloodstream and re-circulated. It contains some white blood cells and supplies nutrients to the brain. Another function is to act as shock absorber for the brain. Its total volume is about 150 milliliters and it is replaced every three to four hours in the adult human. In total then, between 400 and 600 milliliters are produced each day. If it is not kept within normal limits, and the fluid accumulates in the ventricles, it can give rise to hydrocephalus. See Ependymal cell, Hydrocephalus (or hydrocephaly), Neural tube, Ventricle chaos: unpredictable and seemingly random behavior occurring in a non-linear system and governed by deterministic laws. In fact chaos, despite being incorrectly associated with randomness, is fully deterministic. Two hallmarks of chaos are that its behavior never cross the same path twice and that a chaotic system has a sensitive dependence on initial conditions, which means that a very small initial difference can result in an enormous and unpredictable change to the future state of the system (the so-called butterfly effect, first described by Edward N. Lorenz in 1972). For this reason, it has been termed determinism without predictability. Chaotic attractors have fractal dimensions [i.e., a dimension between a line (1) and a surface (2), with a snowflake curve having a fractal dimension of 1.26]. Fractals are irregular shapes or surfaces produced by a process of repeated sub-division, which leads to self-similarity in structure at different levels of organization. See Attractor, Chaos theory, Determinism, Dynamical systems approaches, Levels of organization, Non-linear dynamics, Sensitivity to initial conditions chaos theory: established in 1961 by meteorologist Edward N. Lorenz in attempting to forecast weather systems, it is a branch of mathematics termed non-linear dynamics that focuses on irregular

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and complex behavior that never has an underlying order, and on events and processes that cannot be predicted, except over the short term. Its establishment ended the long-term association between classical determinism and predictability. The mathematical tools of chaos theory have been applied to analyzing brain activity (e.g., by means of EEG) and the spontaneous movements of human infants. See Chaos, Determinism, Non-linear dynamics, Order, Prediction and explanation character: in evolutionary biology, characters, in contrast to traits, are shared similarities, which are regarded as properties (structures or behaviors) in different organisms. They are treated as being heritable and homologous. Differences between homologous characters in different organisms are called character states or modes. A character differs from a character state in that it only specifies a property that is not observable rather than a hypothesis about a homology. Consequently, a character requires a comparison of different organisms as a single organism does not have characters, but only properties. In psychology, there is no real distinction between character and trait. See Evolutionary biology, Homology, Organism, Trait child death: the death of a child at one year of age or later. See Fetal death, Infant death, Neonatal death child development: a vast multidisciplinary area of study that includes, for example, child psychology, child psychiatry, developmental psychology, and pediatrics as well as various sub-fields of biological and cultural anthropology, linguistics, neuroscience and sociology. It is distinguished by methodological pluralism (e.g., experimental and correlational methods), and a range of theoretical and applied concerns. There tends to be a divide between research carried out during and beyond infancy, especially with regard to cognitive development, and some (e.g., Society for Research in Child Development) contend that child development does not include the period of adolescence. In recent years, there has been a noticeable tendency for the study of child development to incorporate theory and findings from evolutionary developmental biology, as well as concerted efforts to relate prenatal and postnatal development in terms of identifying the continuities and discontinuities between them. In the US, the study of child development received formal recognition with the establishment of a sub-committee of the National Research Council in 1922, which three years later became the Committee in Child Development with offices and staff housed at the National Academy of Sciences. See Anthropology, Child psychology, Developmental biology, Developmental cognitive neuroscience, Developmental psychology, Evolutionary developmental biology, Linguistics, Neuroscience, Pediatrics, Sociology child psychology: a branch of psychology supposedly founded by Wilhelm T. Preyer (1841-1897) that typically studies the behavior of children at key ages or makes comparisons between adjacent ages using experimental methods in order to tease out age-specific functions, processes and mechanisms that may be deemed to be cognitive, emotional, social etc. in nature. Often it is used interchangeably with developmental psychology, but strictly speaking there are differences between them, the main one being that the chief concern of developmental psychology should be the study of both intra- and inter-individual differences as a function of age. Child psychology as generally practised does not deal with change in this way, nor with the identification of developmental transitions between states or stages, but at most with age differences in a variable-centered approach. See Child development, Developmental psychology, Intra-individual differences, Transitions, Variable-centered approaches

www.cambridge.org/hopkins © Cambridge University Press THE CAMBRIDGE ENCYCLOEPDIA OF CHILD DEVELOPMENT - Extended Glossary A-C childhood amnesia: the inability of adults to recall early autobiographical memories in the first few years of their lives. Most people report their earliest memory to be between their third and fourth birthdays, and generally memories of childhood do not become a continuous narrative until after about seven years of age. Identified for the first time in 1893 in a publication in the American Journal of Psychology, some years later Sigmund Freud (1916/1966), in his Introductory lectures on psychoanalysis, claimed that childhood amnesia was due to the repression of inappropriate or disturbing content of early, often traumatic sexual experiences. In more recent years, two basic, quite different, explanations for this phenomenon appeared: one is that brain structures critical to memory are too immature during the first few years of life to record long-term memories, and the other that children cannot remember events occurring before they have mastered language. Accordingly, language provides a system of symbolic representation by which people develop narrative stories of their lives. Such a narrative framework may be necessary for people to remember autobiographical events in a coherent context. In the late 1980s, the existence of childhood amnesia was challenged by Robyn Fivush and her colleagues, when they demonstrated autobiographical recall by children only 2.5 years of age, who provided verbal descriptions of unique events experienced six or more months in the past. See Autobiographical memory, Memory cholesterol: a fatty-like, white crystalline substance that is a steroid lipid found in large concentrations in the blood, brain, liver, muscle, spinal cord, and other organs and tissues, with liver being the most important site for its synthesis. Both the liver and dietary intake (e.g., dairy products, fish, meat, poultry) are the main sources of cholesterol. After being synthesized from acetic acid, it then becomes an important precursor for the synthesis of vitamin D3, various steroid hormones (e.g., cortisol in the adrenal glands), and the sex hormones progesterone, estrogen, and testosterone. Also cholesterol provides stability for the membranes of cells, seems to play a role in immune system protection against cancer and in modulating synaptic activity in the brain. Myelin is composed of 15% cholesterol and 20% protein, and thus it has a role to play in brain development as well as with regard to sexual differentiation. Cholesterol is transported out of the bloodstream for excretion by high-density lipoprotein (HDL), and carried back by low- density lipoprotein (LDL) for use by various body cells. Large amounts of HDL cholesterol (the ‘good’ cholesterol) are associated with better health. See Acetic acid, Adrenal glands, Cortisol, Estrogen, Hormones, Lipid, Myelin, Progesterone, Testosterone, Steroid hormones cholinergic neurotransmitter system: a system in the brain using the neurotransmitter acetylcholine that is based in the mesencephalic reticular activating system and which distributes acetylcholine throughout the brain. This system has a widespread energizing influence on brain activity, through both sympathetic and parasympathetic nervous systems, and is closely tied to sustained attention and alerting. Cholinergic receptors binding to acetylcholine are found in both systems. There are two types: nicotinic cholinergic receptors that induce sympathetic postganglionic neurons, adrenal chromaffin cells, and parasympathetic postganglionic neurons to fire and release their chemicals, and muscarine receptors located in peripheral tissues (e.g., end plates of smooth muscle), and associated mainly with parasympathetic functions. In Alzeheimer’s disease (AD), cholinergic neurons, established during the early migratory stsges of embryonic development, are destroyed along with muscarine receptors, according to the cholinergic hypothesis of AD. See Acetylcholine (AcH), Alzeheimer’s disease, Botulinus (or botulinum or botox), Motoneuron, Sympathetic nervous system (SNS), Parasympathetic nervous system (PNS), Sustained attention chondrification: the second phase of skeletogenesis (the growth or formation of the skeleton) during

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embryogensis, it is the process by which dense mesenchyme tissue is converted into cartilage and bone. Chondrification of the vertebrae and limb bones begins in the sixth embryonic week in the human. See Bone Morphogenetic Proteins (BMPs), Embryogenesis, Mesenchyme, Ossification, Musculoskeletal system chordin: a factor or binding protein secreted from the dorsal mesoderm that is involved in the induction of the early nervous system. Moreover, along with noggin, it regulates (or inhibits) Bone Morphogenetic Proteins (BMPs), which is a protein family consisting of nine structurally related proteins belonging to the transforming growth factor beta superfamily, and furthermore plays a key role in craniofacial development. See Blastopore, Bone Morphogenetic Proteins (BMPs), Induction (embryology), Mesoderm, Noggin, Proteins choreiform movements: those resembling the jerky involuntary movements characteristic of chorea, mainly affecting the face and extremetries, and that are prominent under stress. Choreiform movement disorders in children have recently been subjected to treatment trials involving thalamic stimulation. Evident in tardive dyskinesia, their presence has also been been found as a behavioral sign in some juvenile delinquents See Athetoid (or athetotiform) movements, Dyskinesia, Huntington’s disease (or chorea), Tardive dyskinesia chorion: the outermost of two membranous sacs that completely surround the developing embryo and fetus. In mammals, it forms the fetal contribution to the placenta. See Amnion, Chorionic villus sampling, Placenta chorionic villus sampling: the removal and genetic analysis of tissue from villi (hair-like projections of the chorion membrane surrounding the fetus) in the uterus via the cervix during early pregnancy, and used to test for chromosomal abnormalities such as Down’s syndrome. See Amniocentesis, Amnion, Chorion chromatid: one of two thread-like daughter strands of DNA that form when a chromosome divides longitudinally through the action of a spindle during metaphase of mitosis or during anaphase of meiosis to become separate chromosomes, which were held together by one or more centromeres before mitosis began. See Anaphase, Centromere, Chromosome, DNA, Meiosis, Mitosis, Spindle chromatin: located in the nucleus of the cell, it is a complex of genetic material consisting of DNA and proteins that condense to form chromosomes in eukaryotic cell division. Sperm chromatin is different. During spermiogenesis, the chromatin of the male germ cells (spermatogonia) are re- modeled into a more tightly packaged and compact structure, a process associated with the cessation of transcription and involving nuclear protein exchange. See Chromatid, Chromosome, Eukaryote cell (or organism), Nucleus (of a cell), Protein, Spermatogonia chromosome: a threadlike, deeply stained, structure contained in the nucleus of a cell of eukaryotic organisms and composed mainly of DNA and protein in the form of chromatin. Each chromosome consists of two chromatids bound together at the centromere. According to classical genetics, it is the bearer of the genes in a linear order and thus like ‘beads on a string’, which molecular genetics now compares to ‘a string on the beads’. As for all diploid organisms, human cells normally have 46 chromosomes or 23 pairs (22 matched pairs and one pair of sex chromosomes), with one of each pair being contributed by the mother and the other by the father at conception. The number of chromosomes is constant for the somatic cells into which chromatin resolves itself during mitosis and meiosis. The anatomist Heinrich Wilhelm

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Gottfried Waldeyer-Hartz (1836-1921) introduced the term ‘chromosome’ in 1888. Following Augustus Weismann (1834-1914), it was previously referred to as the idant. It was Joe Hin Tjo, in 1955, who defined 46 as the exact number of human chromosomes. See Centromere, Chromatid, Chromatin, DNA, Eukaryote cell (or organism), Germ plasm, Meiosis (or reduction division), Mitosis, Protein, Spindle, Theory of the germ plasm chronological or postnatal age: the period of time since birth measured, for example, in terms of days, months or years. See Corrected age cilia: smaller than flagella, they are microtubular, hairlike structures used by some single-celled organisms for locomotion through liquids. In addition, they cover the cells of certain tissues (e.g., the epithelium lining the lungs), and help these cells clear away fluids or particles. Structurally identical to flagella, the two terms are often used interchangeably. However, cilia is used when they are short and numerous, and flagella when they are relatively long and sparse. See Cell, Epithelium, Flagella cingulate gyrus: an important component of the limbic system, it is a gyrus in the medial part of the brain that partially wraps around corpus callosum, which is constrained from above by the cingulate sulcus, and located between this sulcus and that of the corpus callosum. It receives inputs from the anterior nucleus of the thalamus and the neocortex, projects to the entorhinal cortex via the cingulum, and forms part of the cortico-basal-ganglionic-thalamic circuit. The cingulate cortex is the cortical part of the cingulated gyrus. It functions include the coordination of sensory input with emotions, emotional responses stress, and the regulation of aggressive behavior. Its increased activation is associated with obsessive-compulsive disorder and cue- related cocaine cravings, and disruptions of its connections during development with schizophrenia. See Aggressive behavior, Amygdala, Anterior cingulate gyrus, Corpus callosum, Entorhinal cortex, Gyrus, Limbic system, Obsessive-compulsive disorder, Pulvinar, Sulcus, Thalamus circular (or non-linear) causality: broadly speaking, this form of causality is one in which the cause reproduces itself over time. It can be symbolized in the following way: A √ B (i.e., A effects B, just as B effects A) in contrast to linear causality A ∏ B (i.e., A is the antecedent to or causes B). Also, it is the rate at which [A effects B] changes as [B effects A]. Examples of circular causality from cybernetics are negative (deviation-reducing) and positive (deviation-amplifying) feedback. All told, it boils down to instances of self-regulation, a simple example based on negative feedback being a thermostat to maintain a constant room temperature. Going beyond such simple systems to self-organizing complex systems, circular causality is inferred in the two-way relationship between order and control parameters (i.e., an order parameter at the macroscopical level constrains the behavior of a control parameter at the microscopical level, but in turn a control parameter can change the state of an order parameter when it exceeds some critical value). This interpretation in terms of brain functioning is expressed by Walter J. Freeman as a top-down macroscopic state (e.g., attention) simultaneously influencing the actions of individual neurons at the microscopical level that in turn create and sustain the macroscopical state bottom up. A similar interpretation based on the principles of self- organization can be found in J.J. Gibson’s ecological psychology in which perception and action are depicted as being inseparably linked or coupled via circular causality. See Causality (in philosophy), Control parameter, Cybernetics, Downward causation, Ecological psychology, Feedback, Order parameter, Perception-action coupling, Self-organization, System

www.cambridge.org/hopkins © Cambridge University Press THE CAMBRIDGE ENCYCLOEPDIA OF CHILD DEVELOPMENT - Extended Glossary A-C clades: in cladistics, they refer to taxonomic groups that consist of all species descended from a known or inferred ancestor as well as the ancestor itself. See Cladistics, Cladogram, Species cladogram: in cladistics, a diagram of hypothesized relationships that assigns organisms to taxonomic groups called clades, but which is not the same as a phylogenetic tree as that adds non- phylogenetic information (e.g., times of transition). See Clades, Cladistics cladistics: a method of biological classification using only genealogies in inferring phylogenetic relationships among organisms, which disregards their adaptations as they may not be due to homology. The outcome is a cladogram. See Clades, Cladogram, General theory of biological classification, Homology, Palaeontology, Phylogeny classical conditioning: a form of learning where an initially neutral stimulus is paired with a response- eliciting stimulus (see figure below). See Delay(ed) conditioning, Eye-blink conditioning, Learning, Operant (or instrumental) conditioning

Classical conditioning: unconditioned stimulus (UCS) becomes associated with a conditioned (CS) over repeated trials so that CS comes to reproduce the unconditioned response (UCR) classical thermodynamics: a branch of physics that studies the processes involved in the reversible transformation of heat into mechanical work, of mechanical work into heat, or the flow of heat from a hotter to a colder body. It does so on a more macroscopical level than statistical mechanics. The first and second laws of thermodynamics aid in understanding processes like these. There are two other laws: the third law, or the Nernst heat theorem (as a homogeneous system approaches a temperature of absolute zero, then its entropy tends to zero), and the zeroth law (if two bodies are each separately in thermal equilibrium with a third body, then all three bodies are in thermal equilibrium with each other). See Bridge law (or principle), Entropy, First law of thermodynamics, Irreversible thermodynamics, Open system, Second law of thermodynamics, Statistical mechanics cleavage: the series of mitotic cell divisions from blastomeres during which a single fertilized egg, the zygote, is transformed into a multicelluar body, the blastula. See Blastomere, Blastula, Mitosis, Zygote clicks: sounds common in Khosian languages of South Africa that are produced by sudden release of a closure of a large area of the tongue against the palate. These languages are made up of three branches: the Khoisan languages of the San (Bushmen) and Khoikhoi, spoken in various parts

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of sub-Saharan Africa, Sandawe, found in Tanzania, and Hatsa (Hadzane or Hadzapi), also in Tanzania. Although all the Khoisan languages use click sounds, Sandawe and Hatsa are unlike the other Khoisan languages and are not related to each other. All of the Khoisan languages appear to use tones to distinguish meanings, and the Khoikhoi languages and some of the San languages inflect the noun to show case, number, and gender. However, the outstanding feature of the Khoisan languages is their extensive use of click sounds. Examples of click sounds familiar to speakers of English are the interjection tsk-tsk and the click used to signal to a horse. The sounds, which are found only in Africa as parts of words, involve a sucking action by the tongue, but the position of the tongue and the way in which air is released into the mouth vary, just as in the formation of other sounds. Consequently, clicks can be dental, palatal, alveolar, lateral, labial, or retroflex; voiced, voiceless, or nasal; aspirated or glottal. There are six types of clicks for the San languages, although no single one has all of them. The Khoikhoi languages have dental, palatal, retroflex, and lateral clicks. Some Bantu languages, notably Zulu and Xhosa, which are spoken near the Khoisan area, have borrowed click sounds from the Khoisan languages. Nothing seems to be known about how click sounds are incorporated into speech development. It must be a complicated process as there are more than 100 ways to begin a word with a click. See Glottal, Labio-dental, Lnaguage development, Lateral sound, Lingua-alveolar (or alveolar) climbing fibers: axons projecting from neurons in the inferior olivary nucleus impinging multiple synapses on Purkinje cells in the cerebellum (up to 300 on each of the dendrites of these cells), and which contain the neurotransmitter aspartate. They wind among Purkinje cell dendrites, thereby providing direct input to the only cell in the cerebellum that has a direct output. One of two afferent fiber inputs to the cerebellum, they transmit rhythmical oscillations or action potentials controlled by the other fiber inputs (viz., mossy fibers) that dominate the activity of Purkinje cells. See Action potential, Aspartate (or aspartic acid), Cerebellum (anatomy), Inferior olivary nucleus, Mossy fibers, Neurotransmitter, Purkinje cells clinical neuropsychology: the application of neuropsychological knowledge to the assessment, diagnosis, management and rehabilitation of patients across the life span who have suffered illness or injury (especially to the brain) leading to neurocognitive dysfunctions. In doing so, information provided by other medical or healthcare providers is taken into account. See Neuropsychology clonus: a spasm in which contraction and relaxation of a muscle alternate in rapid succession, usually after a sudden passive stretch, and thus sometimes referred to myoclonus. It is observed as a sustained rhythmical tremor of around a joint (e.g., ankle, patella, wrist). Although it can be due to damage to peripheral nerves, most forms of clonus are caused by problems in the central nervous system. However, the precise mechanisms underlying it are not fully understood, and it is possible that the different forms may have different causes. While associated with spasticity, it can be transitorily present in healthy newborns for a few days after birth. See Spasticity closed-class: a grammatical class of words with limited membership, which have primarily grammatical meaning such as conjunctions (a word conjoining words or phrases or clauses or sentences whose usage increases at 5 years-of-age), demonstratives (a word indicating to which objects a sentence is referring to, with English having four: this, that these and those), determiners (one of a limited set of noun modifiers determining the referents of noun phrases that are ideal for teaching children labels), pronouns (a word used in place of a noun or noun phrase, with most children using them by 3O months), and auxiliary verbs (a verb that provides further

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information about a main verb that follows it, but which under certain circumstances can become the main verb as in “I am mending a puncture”). The closed class is considered to be part of the core language, and as such is not expected to change, in contrast to open words. Also known as a function word. See Grammaticization (or grammaticalization), Open-class, closed-ended interviewing: interaction between a researcher/interviewer and a respondent in which the interviewer presents a prepared set of questions to each respondent in the same words and in the same order, and asks each respondent to select from a prepared set of possible responses. It can be contrasted with open-ended interviewing in which respondents are free to respond in their own words, and interviewers may re-phrase questions, probe for additional information, and construct new questions, so that the content of the interview varies across respondents. See Counter-suggestion, Theory of child’s mind (ToM) closed-loop and open-loop control: terms originating in engineering and transferred to the study of motor control. Closed-loop control refers to control achieved by feedback such that the actual response conforms to the desired response (or set point) by means of correcting any difference between them. The feedback path, input to output and back to input, forms what is called a closed loop (e.g., monosynaptic reflex arc, cortico-cerebellar loops). In contrast, open-loop, or predictive control, involves control only by an input signal, without the benefit of feedback. In this form of control, the input signal is amplified so as to drive the motor to perform the desired outcome. Aiming movements of the hand toward a target that are performed too quickly for proprioceptive feedback to have occurred are typically given as an example of open-loop control. In engineering, closed-loop control systems are generally preferred to those based on open-loop control because they respond and move the loads they are controlling quicker and with greater accuracy. In the study of motor control, however, it was realized in the 1970s (mainly through the work of Emilio Bizzi) that the models based on the closed-loop control of movements had a number of shortcomings, Chief among these is that there are considerable propagation delays in provision of sensory feedback in various modalities that could not account for the likes of fast aiming movements (e.g., simple and choice visual reaction times are in order of 230 and 420 ms, respectively). The explanation offered for such movements is that the central nervous system determines in advance the trajectory and the ratios of muscle co-contractions. As consequence, the role of closed-loop control was restricted to slow and fine modifications of posture, adjustments made to new or odd postures, and motor learning. Current models of motor control involve combinations of both forms of control in order, for example, to account for the interaction between movement and posture in the execution of goal-directed actions such as reaching and grasping. Simplified representations of closed-loop and open-loop control are presented in the figures below. See Feedback, Motor control, Monosynaptic reflex arc, Motor learning, Prospective control, Reflex arc, Trial-and-error learning

Closed-loop control based a feedback control system

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Open-loop or predictive control closed system: a system that is functionally isolated from its environment. As such, it does not exchange energy, information or matter with its environment and thus obeys the second law of thermodynamics or the law of entropy. Consequently, it will irreversibly deteriorate with time to a state of entropy or maximum disorder. See Energy, Entropy, Information, Matter, Open system, Second law of Thermodynamics cluster reduction: a phonological pattern of deletion of one or more elements in a consonant cluster as in ‘tick’ for ‘stick’. A feature used when children do yet has complete master mastery over the pronunciation of words. If it persists, it can become a speech difficulty in children, See Consonants, Phonology co-evolution: a term devised by Paul Ehrlich and Peter Raven in 1964 that refers to the reciprocal evolution of two or more interacting species, a process that requires a long association. Bees and pollinating flowers are two highly co-evolved species showing a high degree of interdependence and demonstrate reciprocal selective forces resulting in the evolution of one species affecting the selective forces upon the other one. Another example is sexual selection involving female choice and male secondary sexual traits, which amounts to co-evolution within a species. See Cultural and biological evolution, Natural selection, Species, Theory of sex selection co-factor: an accompanying condition, circumstance, or characteristic necessary or sufficient to produce a particular outcome, result, or event. In biology, for example, it is a non-protein substance essential for one or more related enzyme reactions. See Enzyme, Necessary and sufficient conditions co-occurrence learning: learning what words can occur before or after a given word. See Grammaticization (or grammaticalization), Language development, Statistical learning co-sleeping: refers to a diverse, generic class of human-wide sleeping arrangements (mother-infant, husband-wife-children, brother-sister, etc.) wherein at least two or more persons sleep within proximity or close enough to permit each (or all) to detect, monitor and exchange sensory stimuli (e.g., odors, sound, movement, touch, gaze etc.). Considered by some to a protective factor against sudden infant death, it is opposed by others who regard it as unnecessary risk for crib death, a controversy that is becoming increasingly vitriolic in tone. See Sudden infant death syndrome (SIDS, cot or crib death), Protective factor, Risk factor co-twin method: a method for comparing the development of monozygotic twins in which one is given regular practice or training on a specific ability or a range of them, while such experiences are withheld from the other twin. If practice does not make a difference, then it taken as evidence that the environment plays little role in development and thus it is genetically determined. In its

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original form, this method would not now meet with ethical approval, but it finds an echo in behavior genetics when attempting to dissect hereditary and environmental contributions to the development of a range of traits by means of comparing monozygotic and dizygotic twins using a range of sophisticated statistical techniques. See Behavior genetics, Dizygotic twins, Hereditary, Monozygotic twins coccal infections: infections with certain bacteria, including streptococci (e.g., cause scarlet fever, sore throats and tonsilitis in humans), and staphylococci (e.g., cause boils, meningitis and septicema). It was by means of a contaminated culture plate of staphylococci that Alexander Fleming (1861-1955) discovered penicillin for which he shared the Nobel Prize for Physiology or Medicine in 1945. See Memingitis cochlea: a spiral-shaped organ of the inner ear that detects frequency variations in incoming sound waves. With high-pitched sounds, one end of the cochlea is activated, while a low-pitched one does so for the other end. The sounds, as standing waves, displace the stereocilia on the tips of the hair cells, which are then polarized by the wave leading to vesicles in the cells releasing neurotransmitters into the auditory nerve. When the hair cells are damaged, this leads to sensorineural hearing loss. The function of the cochlear implant is to replace these hair cells. See Auditory (or acoustic) nerve, Cochlear implant cochlear implant: used in deaf children before they have acquired to ability to use language, it converts speech into electrical pulses that the auditory nerve can process. It consists of an microphone that is fitted outside the ear, which receives speech sounds. The microphone amplifies the sounds into a speech processor linked by a cable, and then converts the sound into electrical signals sent to a transmitter that is fastened to the head. The transmitter then sends the coded electrical pulses to an multichannel electrode (i.e., a receiver-stimulator) connected to the cochlea through a bundle of wires that activate the cochlea to send signals to the auditory nerve and the brain. There is some concern expressed in the deaf community that cochlear implants will lead to the ultimate destruction of the deaf culture. See Auditory (or acoustic) nerve, Cochlea, Cranial nerve cochlear nucleus: the portion of the medulla in the lower brain stem to which the auditory nerve connects. This area is organized by frequency responses characteristics. Located on the floor of the fourth ventricle, it is the first relay station in the auditory nerve. See Auditory (or acoustic) nerve, Cochlea, Cranial nerve, Ventricle coding scheme: a set or sets of mutually exclusive and exhaustive categories used when coding behavior, either live or video recorded or from transcripts. See Generalized sequential querier (GSEQ), Interval recording, Lumping (versus splitting), Sequential data interchange standard (SDIS), The Observer, Zero-one time sampling cognition: a generic term involving high level functions such as recognizing, concept formation, imagining, judging, problem solving, reasoning, remembering, and thinking. Applied to the social domain (i.e., social cognition) it refers to how people select, interpret, remember, and use social information to make judgments and decisions. It is intimately related to perception and difficult to distinguish from it as, for example, when studying attentional processes. Perhaps the first person to use the term ‘cognition’ was St Thomas Aquinas (1225-1274) who regarded it as ‘how we know the world’ and distinguished it from ‘affect’ (feelings; emotions) and conation (the act of willing something). On this basis, cognition as a general concept came to mean psychological processes or functions for acquiring knowledge and understanding the

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world. See Attention, Cognitive structures, Cognitive development, Perception, Problem solving, Reasoning (psychology) cognitive behaviour therapy (CBT): developed from Ellis and Beck’s cognitive theories of depression, it aims to challenge and eliminate negative distortions and replace negative automatic thoughts with alternative adaptive thoughts by using logical analysis and behavioral experiments. Behavioral techniques include increasing rewarding activities (activity scheduling), decreasing behavior that is followed by unpleasant consequences, training of family/friends to praise/encourage constructive behaviors and not to reinforce depressive behaviors, and assertiveness and social skills training. Used in the treatment of children with Attentional Deficit Disorder. See Attentional Deficit Disorder (ADHD), Behavior modification cognitive development: in very general terms, the development of abilities necessary for understanding and organizing the world and including, for example, the acquisition of those required for discrimination, memory and problem solving. Piaget’s genetic epistemology had a major impact on conceptualizing and studying cognitive development, with his functional universals of assimilation and accommodation interacting in the process of equilibration. In more recent times, the theory of embodiment is beginning to have an impact on theorizing about the nature of cognitive development: the acquisition of knowledge is attained through exploratory cycles of perception and action that result from a brain interacting with a body and the body interacting with the external world. See Accommodation, Assimilation, Cognition, Cognitive immaturity hypothesis, Developmental epistemology, Embodied cognition, Embodiment, Equilibration, Perceptual development, Sensorimotor action cognitive-functionalist approach: in linguistics, the view that language structure is shaped by the semantic and pragmatic properties of the messages being communicated, and by the mechanisms of language perception and production. Standing in contrast to the ‘generative approach’, it holds that the function of language (viz., communication) constrains the range of grammatical rules both between and within natural languages. Linguists favoring the cognitive- functionalist approach consider grammar to be a system for coding relationships between utterances and their meanings, and that grammar is an inventory of mappings between utterances and their pragmatic and semantic interpretations. The coding system is thought to bear the following features: 1. grammatical rules consist of utterance-meaning pairs, which are not necessarily represented in an explicit way, 2. production and comprehension of novel expressions derive from regularities between input-output pairs, 3. the manipulation of conventional expressions underlies much of grammatical competence, 4. when similar patterns reinforce each other, prototypes emerge, 5. frequency of use maintains any irregular grammatical patterns, and 6. a diverse set of cognitive abilities constrains the linguistic coding of events. In recent years, connectionist models have been increasingly used to test some of the claims of the cognitive-functionalist approach (e.g., using backpropogation networks to extract regularities and the degree to which they resemble how speakers detect cues in meaning). See Backpropogation, Connectionist models, Generative grammar approach, Linguistics, Pragmatics, Semantics, Transformational grammar approach, Utterances cognitive immaturity hypothesis: the argument that younger children have less mature cognitive capacities, so that benefits of concentrating on a cognitively demanding task decrease after a shorter time than for older children. Benefits, however, can be increased through taking breaks for play. A key feature of the hypothesis is that the cognitive abilities of children are not inferior variants of adult behavior, but rather specific adaptations to the niche of childhood that enables young children to learn new abilities in an effective way. Consequently, play is accorded an

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important role in the hypothesis. See Cognitive development, Play cognitive neuroscience: an integrative area of study (in fact, it comes close to being an interdiscipline) that draws mainly from cognitive psychology, cognitive science, neuroscience and linguistics to study the neural dynamics of psychological functions such as face processing, intra- and inter- hemisphere processing, learning and memory, and the development of such functions, using brain mapping and imaging techniques. It has been said that it evolved from dissatisfaction in neuropsychology with a lack of models for understanding the effects of circumscribed forms brain damage (e.g., parietal lobe lesions) on cognitive performance tests, and which were to be found in cognitive psychology. Currently, its practitioners follow one of two broad directions: experimental behavioral research, often involving brain imaging, and computational or neural network modeling. See Brain (neuro-) imaging, Cognitive psychology, Cognitive science, Computational models, Connectionism, Developmental cognitive neuroscience, Interdiscipline, Linguistics, Neuropsychology, Neuroscience, Psychology cognitive psychology: the branch of psychology that studies the processes and mechanisms underlying all forms of cognition, mainly by experimental methods. To begin with, it was based on testing information-processing models of cognitive functioning, but in recent years these models have been challenged by dynamical systems approaches and the theory of embodiment. The term appeared for the first time in Ulrich Neisser’s book Cognitive psychology (1968), but its birth was probably witnessed at the Hixon symposium (1948) and facilitated by the theorizing of Donald Broadbent (1926-1993) in his book Perception and communication (1958), as well as by Plans and the structure of behavior (1960) written by George A, Millar, Eugene Galanter and Karl A. Pribram. See Cognition, Cognitive science, Cognitive neuroscience, Dynamical systems approaches, Embodiment, Hixon symposium, Information-processing theories, Neuropsychology, Psychology cognitive science: a multidisciplinary field of research that draws upon anthropology, artificial intelligence (e.g., symbolic information-processing models, neural networks, machine learning), cognitive psychology, computer sciences, epistemology, linguistics, neuroscience, and philosophy (especially philosophy of mind and of mathematics). Its overarching goal is to answer long-standing epistemological questions about the nature of knowledge, its sources and component parts, and how it develops. As a consequence of such a goal, it addresses a diversity of topics that include attention, consciousness, intuition, perception, problem solving, and reasoning. Cognitive science is a direct outcome of the so-called cognitive revolution that originated in the mid-1950s when there was an upsurge of interest in theories of mind based on complex representations and computational procedures. It became distinct from cognitive psychology with the formation of Cognitive Science Society in the mid-1970s. In its relatively short existence, cognitive science has achieved much, particularly with regard to models of human cognitive bias and risk perception. It has been responsible for a new theory of the philosophy of mathematics, and a range of theories covering artificial intelligence, persuasion and coercion. Moreover, it has become firmly established as integral part of modern linguistics. See Artificial intelligence (AI), Cognitive psychology, Hixon symposium, Interdiscipline, Linguistics cognitive structures: general principles or concepts that underpin knowledge, reasoning and understanding. For learning to occur, it must be incorporated into existing cognitive structures, from which it follows that new experiences and prior knowledge overlap. See Behavior mechanism, Cognition, Reasoning (psychology), Scheme

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Cohen's kappa coefficient: an index of the extent to which two observers agree when applying a nominal scale (i.e., a set of mutually exclusive and exhaustive categories) that corrects for chance agreement, and which provides a measure of inter-rater reliability. Kappa (K) is calculated by means of the following formula:

PA - PC K = 1-PC where PA = proportion of units on which raters agree (percentage of agreement) Pc = proportion of units for which agreement is expected by chance

Resultant K values have been accorded the following strength of agreement interpretations: slight (0.00-0.20), fair (0.21-0.40), moderate (0.41-0.60), substantial (0.61-0.80), almost perfect (0.81-1.00). An example of computing K is given in the table below. See Cronbach’s alpha, Inter-rater reliability

Rater 1 Smile Frown Neutral face Total Smile 42 (30) 10 (21) 5 (7) 57 Rater 2 Frown 7 (18) 25 (18) 3 (5) 35 Neutral face 1 (4) 2 (3) 5 (1) 8 Total 50 37 13 100 Values between parentheses are the expected frequencies or chance associations PA = 42 + 25 + 5/100 = .72 PC = 30 + 18 + 1/100 = .49 K = .72 -.49/1 - .49 = .451 cohort: a number of people who share a common characteristic linked to a specified place and time (e.g., born in a particular geographical location over a specified time period or the year of marriage). There are many different kinds of cohorts, examples being: the birth cohort of 1958 is comprised of all individuals born in that calendar year, while the marriage cohort of 1982 consists of all individuals married in 1982. The origin of the word derives from the Latin for a unit of the Roman Legion (i.e., a division) consisting of 300 to 600 men. See Cohort effect, Community, Population cohort effect: a characterization of a group such as a the mean of a variable or an association between variables that changes for persons born at different times or places. In cross-sectional studies, this effect can give rise to inappropriate conclusions about the nature of developmental change. A well-worn example is finding that IQ appears to decline with age from early adulthood onward when, in fact, younger cohorts tend to have higher mean IQs than older ones as a consequence of better nutrition, schooling and the like (something known as the Flynn effect) See Cohort, Cross-sectional design, Flynn effect, Longitudinal studies colic: this term refers to prolonged, unexplained crying in 1-3 month-old infants. It is poorly defined and may be used to refer to amounts of crying, to the inference that the crying is caused by gastrointestinal pain, or to the reports of parents that the crying is a problem. Here, it is used broadly to refer to prolonged bouts of crying that occur without apparent reason in 1-3 month- old infants, together with parental concern about the crying. See Crying, Fussing, Intolerance for cow’s milk protein

Command paper: a document issued by the British government setting out its position with a view to

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legislation or executive control. It is a command in two respects. Historically, the British government is the constitutional expression of the commands of the British monarch. Formally, any command is a particular type of regulation and so has normative properties. See Education, Normative common coding: a recent hypothesis in cognitive neuroscience, put forward by Wolfang Prinz in 1997, stating that perception and action are not independent systems, but rather share resources and mutually influence each other. Thus, action perception and action planning draw on common psychological codes and amodal representational frameworks. As suggested by Prinz, common coding may most appropriately apply to ‘high-level’ processing at cognitive levels of representation. There is as yet no conclusive evidence in support of a well-identified neural substrate for a common coding between perception and action. Nevertheless, the hypothesis, a close cousin of the two visual systems hypothesis, continues to have an important influence on studies of imitation as it holds that action planning is activated during perception. See Active intermodal matching (AIM), Amodal, Cognitive neuroscience, Correspondence problem, Dorsal visual pathway (or stream), Imitation, Mirror neurons, Perception-action coupling, Shared neural representations, Representation (mental), Two visual systems hypothesis, Ventral visual pathway (or stream) communication: a process occurring when a person transmits a message to another person who receives it. The message may be comprised of verbal (e.g., thoughts, feelings) or non-verbal information (e.g., gestures, emotional expressions) or both. Both the person transmitting the message and the person receiving it must share a common code (e.g., system of shared symbols, signs, or behavior) for communication to be successfully transmitted from person to person. See Co-regulation, Conversational contexts, Conversations, Interaction, Shared reference, Signs, Symbols community: a well-defined assemblage of populations inhabiting a common environment. Communities are usually named with reference to a dominant species’ feature (e.g., a community of rhesus monkeys) or a prominent physical feature (e.g., a community of mountain dwellers). See Cohort, Community survey, Ecology, Levels of organization, Population community survey: a research design in which conclusions are intended to be drawn about the whole of the people in the community (usually defined geographically), or a particular sub-group within it. Attention is therefore given to the representativeness of the sample from which data are recorded. See Community, External validity, Generalization co-morbidity: the co-occurrence of two or more disorders in the same individual, and usually used in relation to psychiatric disorders, with reference to an initial diagnosis. Put another way, it is the presence of one or more disorders (or diseases) in addition to a primary disease or disorder, and the effect(s) of such additional disorders or diseases. Co-morbidity may affect the ability of individuals to function and survive. Distinguishing the primary disorders from the secondary disorders is a major issue in diagnosis, especially when concerned with developmental disorders. See Developmental disorders, Diagnosis (or diacrisis) comparative method: the combined evaluation of both similarities and differences in behavior and its roots across species, developmental periods, individuals, and cultures. In linguistics, is it is method to detect genetic relationships through reconstructing the common ancestor of the languages under consideration, and by devising a plausible sequence of regular changes that originated from a common ancestor. See Analogy (biology), Canon of parsimony, Cross-

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cultural psychology, Ethology, Homology, Linguistics, Serial homology competence (embryology): a reactive state permitting directional development and differentiation in response to a stimulus or organizer. What constitutes an organizer, a concept originally introduced into embryology by Hans Spemann (1869-1941), continues to be a topic of intense research. The concept of competence in embryology is closely associated with that of sensitive period. In biology, more generally, it refers to the ability of a cell, typically a bacterium, to take up DNA and be genetically transformed. See Differentiation (specific), Embryology, Induction, Organizer, Sensitive period competence (linguistics): also referred to as linguistic competence, it was brought into linguistics by Noam Chomsky to refer to an idealized mature speaker’s underlying knowledge of the grammatical rules of a natural language, in particular generative grammar and transformational grammar, something he contrasts with performance. Competence in this sense, according to Chomsky, who labeled it formal linguistics, can only be studied if natural languages are regarded as mental objects. See Generative grammar approach, Linguistics, Performance (linguistics), Transformational grammar approach competence (psychology): the display of (age-) adequate abilities or skills for a particular task or situation. While this definition applies to individuals, the concept of competence can be extended to the group level. Like intelligence, it covers a number of different areas such as perceived competence, physical competence and social competence, See Ability, Developmental readiness, Intelligence, Self-competence, Skill, Self-perception competitive exclusion model: a model of imprinting proposed by Patrick Bateson that posits experience with the imprinting stimulus as the causal factor for the end of the sensitive period. The model also holds that exposure to an imprinting object makes another one less effective, and leads individuals (chicks in this case) to prefer the one to which they have been exposed and to reject anything perceived as being different. Thus, experience of one sort excludes other forms of experience from having the same effect. The model has some similarities with the competitive exclusion principle (Gause’s rule) in community ecology: if two species occupy the same niche, one will eventually outcompete the other in harvesting more resources and reproducing more efficiently, thereby leading to the latter’s extinction. See Community, Ecology, Imprinting, Niche, Sensitive period complexity: a difficult-to-define concept. Intuitively, complexity is usually greatest in systems whose components form intricate patterns and lowest when a system is either highly regular or completely disordered. Complexity is also applied to systems in which the outcome of some process is difficult to predict from its initial state. There are two broad classes of complexity: static complexity as in the intuitive notion of complexity, and dynamical complexity in terms of how much computational effort is required to describe the information content of a state of a system. A system can have low static complexity (or rather simple structures) and yet display complex dynamical behavior. See Dynamical systems approaches, Information, Open system, Pattern formation, State (phase) space, System composite (or sum) scale: a scale giving a score created by aggregating several of the items in a questionnaire or set of tests (e.g., sub-scales of an IQ test). An important psychometric consideration in the derivation of multi-item composite scales concerns their internal consistency. See Cronbach’s alpha, Internal consistency

www.cambridge.org/hopkins © Cambridge University Press THE CAMBRIDGE ENCYCLOEPDIA OF CHILD DEVELOPMENT - Extended Glossary A-C compound symmetry: constant variances and constant covariances of the dependent measure across the levels of a factor in analysis of variance. This property of the variance-covariance matrix is present when the main diagonal elements of a set of multivariate data are equal to one another, which must also be the case for the off-diagonal elements. It is a condition that is important in the analysis of longitudinal data. See Analysis of variance (ANOVA), Longitudinal studies, Mauchly test, Patterns of variances and covariances, Repeated measures analysis of variance, Sphericity, Sphericity assumption, Variance-covariance matrix computational models: computer programs that are used to explain different aspects of cognitive and behavioral development and processing (e.g., balance scale task). A computational model implements a theory of development and can be used to test this theory and to generate predictions that can be tested empirically. Undoubtedly, one of the founders of computational modeling was Alan Turing (1912-1951) and his eponymous machine. The Turing machine is an abstract or hypothetical automaton consisting of tape and a reading head, with tape moving back and forth under the head. In doing so, it marks and changes the symbols (e.g., 1 and 0) on the head one by one using the information it is supplied with. The activity of the machine is jointly determined by its current state and the symbol being read in the current frame. Turing launched his machine in 1937 before the invention of digital computers, yet stripped of its now arcane terminology is in essentially like a modern computer. Advances since Turing’s time have resulted in parallel computational models in which computers are linked together in tandem to process complex sets of data in which items of knowledge are represented by patterns of connections of different strengths between distributed locations within a neural network. The task then is one of ensuring parallel processing of collections of these activated connections to produce some desired outcome (e.g., resolution of the balance scale test). See Balance scale test, Category learning, Cognitive neuroscience, Connectionist models, Neural net concept: an abstract idea inferred or derived from particular instances (e.g., cognition, temperament). Concepts can also represent physical objects such as a table and chair as well as their relationships. They serve to relate facts to theories and propositions, and in this way can become variables. A concept, however, is more encompassing than a variable. So, for example, status and role are concepts, while ranking status according to social class is a variable. See Construct, Variable conditional knockouts: usually transgenic animals in which specific genes can be knocked out (or deleted) only in certain cells or at certain times under experimental control in an attempt to identify what effect that gene has in the life of the organism. The mouse is unique among mammals with regard to the degree to which its genome is amenable to such genetic manipulation, and the production of gene knockouts has become a routine task for identifying genes responsible for a range of diseases (e.g., Huntington’s disease). Thus, mice are good for reverse genetics, but not forwards genetics. Progress in producing mice with conditional knockouts at certain stages of development when genes are inactive or that can be turned off and on using drugs and environmental changes has proved more difficult to achieve. In contrast, knock-in mice are generated to study the exogenous expression of protein through the insertion of a transgene at a selected locus on the chromosome. See Forward genetics, Reverse genetics, Transgene conduct disorder: a psychiatric diagnosis, created by the American Psychiatric Association, for children who violate age-appropriate social norms and rules, especially by physically aggressing

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persons, damaging property, stealing, running away from home, and not going to school. Thus, it is a consistent pattern of socially non-acceptable, norm-breaking behavior leading to functional disability. Conduct disorder has been associated with family conflicts, child abuse, poverty, genetic defects, and parental drug addiction or alcoholism as well as being more common in children with Attentional Deficit Hyperactivity disorder. More common among boys, it is estimated to be as high as 10% in the US. See Aggressive behavior, Attention deficit hyperactivity disorder (ADHD), Behavioral problems, Bullying, Oppositional defiant disorder configural processing: assignment of the spatial relationships between facial features during face processing. Face processing involves not only configural or holistic processing, but also featural processing, and the question of interest is how they interact in the development of facial recognition. A dissociation between configural and featural processing of faces can be seen in comparing autistic and Williams syndrome children. Autistic children appear to have a relative strength in the configural or holistic processing of faces, and those with Williams syndrome for processing the features of faces as shown by the inverted presentation of faces. See Autism, Face recognition, Face processing, Williams syndrome confirmatory factor analysis (CFA): a type of factor analysis where the specific number of factors and the pattern of the zero and non-zero loadings are hypothesized apriori and in advance of the estimation. CFA is often used to compare one specific alternative factor model hypothesis to another. See Exploratory factor analysis (EFA), Factor analysis, Factor loadings confound: means literally to throw something into disorder. In the research context, this term is used when there are two or more explanations for a significant result, usually because a study cannot control extraneous variables. See Causal pathway, Confounding variable, Contamination confounding variable: a unforeseen and unaccounted-for factor that generates an apparent association between two variables because it has a prior association with both. For example, height and school achievement may both be associated with socioeconomic status. Thus, an apparent link between size and success could be said to be subject to confounding by social class. Such a variable jeopardizes both the reliability and validity of a study. See Causal pathway, Confound, Contamination, Reliability, Validity, Variable congenital abnormalities: major disorders present at birth (including congenital malformations), and acquired during uterine development, which can be the result of disease, drugs, or an abnormal chromosomes or genes. See Congenital anomalies, Congenital malformations, Developmental disorders, Syndrome congenital anomalies: relative to congenital malformations, they are minor disorders such as polydactly (presence of more than ten finger or toes), and a large earlobe that are one of the less devastating outcomes associated with inbreeding. They occur in a further 2.5% of live-born infants in addition to those with congenital abnormalities. See Congenital abnormalities, Congenital malformations, Developmental disorders, Syndrome, Teratogens congenital malformations: deformities acquired early in development and prior to detection by ultrasound, noted only at birth. They are present in 2.5% of all live births. Some 20% are genetic in origin, or due to drugs such as anti-convulsants and thalidomide taken by the pregnant mother, or to the effects of radiation. The remaining 80% can be ascribed to ‘genetic

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make-up predisposes, environment disposes’. The relative frequencies of some congenital malformations in the UK. are presented below. See Aortic hypoplasia, Anencephaly, Congenital anomalies, Down’s syndrome, Hyrocephalus, Spina bifida, Teratogens

club foot: 19% cardiac abnormalities: 18% spina bifida cystica: 13% hydrocephalus: 11% anencephaly: 9% cleft lip/cleft palate: 8% Down’s syndrome: 7%

CONLERN: a term coined by John Morton and Mark Johnson in their two-process modularity theory of infant face recognition to reflect the infant’s acquisition of face knowledge by virtue of experience in viewing faces. Presumed to be mediated cortically and appearing at about 2 months of age. See Configural processing, CONSPEC, Face processing, Modularity connectionism: a theoretical framework in which networks of interconnected nodes (analogous to neural networks) process information through an activation dynamics while their connectivity evolves according to learning dynamics. Connectionist networks receive inputs that ultimately arise from sensor systems. Particular output layers are assumed to ultimately determine behavior. By generating activation at the output nodes in response to sensory inputs, connectionist networks processes information. Through the learning dynamics, the connectivity of the network over the long run comes to reflect the sensory environment of the system. See Activation, Computational models, Connectionist models, Neural net connectionist models: a class of computational models that consist of a number of interconnected simple processing units. Often the units are arranged in several layers. Connectionist models learn from experience, and have been used to explain several aspects of infant cognitive and behavioral development, as well as developmental disorders. In addition, connectionist models and neural networks have given rise to computational neuroscience, another example of a new emerging interdiscipline that draws on computer science, neuroscience and applied mathematics to gain sights into the functioning of the nervous system. The origins of computational neuroscience reside in the work Alan L. Hodgkin (1914-1998) and Andrew F. Huxley in deriving the first mathematical model of the action potential for which they received the Nobel Prize for Physiology or Medicine in 1963 (together with John C. Eccles, 1903-1997). See Action potential, Cognitive-functional approach, Computational models, Interdiscipline, Neural net conscience: internalization of the rules and restrictions of society; it determines which behaviors are permissible and punishes wrongdoing with feelings of guilt. Having a conscience can lead to conscientious acts, such as conscientious objection, which may be instigated for secular or religious reasons. See Guilt, Moral judgments, Morality consciousness: a phenomenon that the philosopher William James (1842-1910) likened to a ‘stream’ or process by which a sense of self is attained through a succession of experiences. The pragmatist John Dewey (1859-1952) added that consciousness is an emergent property of sentient creatures, which develops and enables discrimination and choice based on the satisfaction of needs and desires. He also argued that, while consciousness involves privately experienced states, categorical thinking must be communicable or based on shared meanings

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to sustain self-consciousness. Other pertinent features of consciousness have to do with the limited capacity of the brain to sustain perception and memory. Attention controls access to consciousness and memory establishes the extent to which on-going events can be re- categorized to include novel and unexpected situations. Some developmental psychologists (e.g., Myrtle McGraw; Jerome Kagan) have contended that infant sensitivity to balance, novelty and discrepancy paves the way for the emergence of consciousness by stimulating the neural mechanisms of arousal and attention. Neuroscientists, however, remain divided about the neural correlates of conscious states. Some contend (Michael Posner) that consciousness is strongly correlated with the firing patterns of neurons in specific brain regions, while others believe (Gerald Edelman) that consciousness involves the synchrony and coherence of widely distributed neuron groups. See Arousal, Attention, Theory of neuronal group selection (TNGS) conservation: in general, the concept that some quantitative aspect of an entity remains unchanged despite a transformation in its appearance. Piaget devised a series of tasks to test children’s understanding of conservation in a variety of entity domains (e.g., mass, number, volume, weight). For example, in conservation of mass tasks, children are tested on whether or not they understand that two identical balls of clay will have the same amount (mass) even if one of them is rolled out into a sausage. In terms of number, if two rows containing equal numbers of counters are presented in one-to-one alignment, and then the counters in one row are moved closer together, the number of counters in the two rows remains the same. See Décalage consonants: sounds produced by various forms of closure of the oral passage, as in the first sound of ‘pill’. See Babbling, Bilabial, Cluster reduction, Diagraph, Vowel-to-consonant ratio, Vowels

CONSPEC: a term coined by Morton and Johnson, and the other part of their modularity theory, to reflect an innate bias or disposition of infants to orient to face-like stimuli in the first two months of life. Presumed to be mediated by the superior colliculus. See CONLERN, Face processing, Innate, Superior colliculus conspecific: a member of the same species. See Species constraint: a condition that preserves the symmetry of a system and restricts its degrees of freedom. When the system is perturbed, it may lead to symmetry breaking. Applied to behavior, a constraint is a boundary condition that eliminates or restrains certain configurations of action while permitting or enabling others. There are two classes of constraints: holonomic or law- governed constraints that restrict without having any material embodiment in the system (e.g., Newton’s laws of motion) and non-holonomic or rule-governed constraints that are physically embodied in the system (e.g., a schema) and which serve as prescriptions for action. Computational models incorporate the latter constraints (e.g., model architecture, training algorithm, training regime). In terms of cognition, a constraint is anything that makes representational development selective in what becomes represented or how the representation occurs. Typically, a constraint has the function of guiding the child's learning within biological boundaries to the extent to which the child can process information and prepare action. In developmental biology, four classes of holonomic constraints are recognized: developmental constraints, physical constraints, morphological constraints and phyletic constraints. See Adaptation, Canalization, Computational models, Control parameter, Degrees of freedom (or Bernstein’s problem), Developmental biology, Information- processing theories, Newton’s laws of motion, Schema, Self-organization

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construct: relationships between a number of objects or events and thus not much different from a concept. However, a hypothetical construct is where a process is not directly observable or objectively measurable, but is assumed to exist because it gives rise to measurable phenomena. In the past, Karl Pearson (1857-1936) suggested it as a substitute for concept. See Composite (or sum) scale, Concept, Construct validity construct equivalence: the measurement principle asserting that a construct or factor can be measured under different circumstances or at different occasions yet still retain its basic property. In practice, several levels of equivalence may be investigated, including factor loading equivalence (or factorial invariance) and factor score equivalence. See Construct, Construct validity, Factor analysis, Factor loading, Replicability construct validity: the process of assessing the significance and utility of a measure by examining whether it predicts associations (and lack of associations) with other variables in the way predicted by the theoretical concept being studied. See Construct, Convergent equivalence, Discriminant validity, External validity, Internal validity, Validity constructivism: the philosophical idea that knowledge and meaning are constructed by action on objects and are neither innate nor simply transmitted through experience. Constructivists believe that events have no meaning by themselves, but instead that individuals must create meaning through the application of existing actions or ways of knowing. It is the epistemological theory that underlies Piaget’s approach to cognitive development. Radical constructivism holds that all kinds of experience are in essence subjective and that no two individuals share the same experience, language being a case in point. See Cognitive development, Bridging, Developmental epistemology, Foundational knowledge, Nativism, Solipsism contamination: the influence of one measure of behavior upon the measurement of another (e.g., if parents know how a teacher has rated their child and modify their own rating accordingly). See Confound, Confounding content analysis: also called textual analysis and first used in 1910 by Max Weber (1864-1920), one of the founders of sociology, it is the systematic coding of the contents of a text or narrative using a variety of techniques based on emergent or apriori rules of coding. In emergent coding, categories are established after some preliminary examination of the data by two or more individuals, with differences in initial checklists being reconciled before arriving at a consolidated checklist. With apriori coding, categories are established before the analysis based on some theoretical perspective. Individuals agree on the categories and coding, which are then applied to the data, with revisions being made to ensure maximal exclusivity and exhaustiveness. Content analysis emphasizes the search for contexts, underlying meanings, patterns and processes, rather than the quantity or numerical relationships between two or more variables. It has wide application, covering topics in fields ranging from marketing and media studies, to literature and rhetoric, ethnography and cultural studies, gender and age issues, sociology and political science, psychology and cognitive science. It has proved useful in, for example, for determining authorship, examining patterns in documents, and for monitoring changes in public opinion, More specific examples include the examination of children’s essays for emergent themes, and the reactions of children to television programmes and advertising directed at them. Sophisticated software packages exist for carrying out many of the routines required by content analysis. See Discourse analysis, Qualitative research context (cultural): the ecological and social environment in which individuals function and that they

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share with members of a larger group (e.g., ethnic group or national group). See Contexts (of expression), Culture, Cross-cultural psychology, Environment context (interview): that which surrounds or accompanies a behavior or event. For example, the verbal or linguistic context of a question in an interview may include the other questions and answers that preceded it. The non-verbal or non-linguistic context may include the interviewer’s non- verbal behaviors (e.g., gestures and facial expressions), salient props (e.g., pictures, toys or other objects) and actions carried out by the interviewer and/or child (e.g., picking up a toy). Broader aspects of the context would include where and when the interview took place, the degree of familiarity between the interviewer and child, and the formality/informality of the interviewer’s style. See Closed-end interviewing, Conversational context contexts (of expression): variations in behavior and its control that occur as a function of internal and external events. See Context (cultural) continuous performance task: a type of computer-based task that demands active cognitive performance over an extended period. Good performance in such a task requires extended periods of sustained attention, and extended activation of brain areas involved in sustained attention. Children with attention deficit hyperactivity disorder show deficits on continuous performance tasks, which are taken to imply deficits in the brain regions controlling sustained attention. A frequently used instrument for the assessment of continuous attention in such children is Connors’ Continuous Performance test (CPT II) that to be able to distinguish response patterns such as inattentiveness and impulsivity. Continuous attention involves the selective awareness of stimuli that are always presented or for most of the time, and in this respect is not the same as vigilance that requires reactions to stimuli presented randomly for a few times over a longer period of time. See Attention, Attention deficit hyperactivity disorder (ADHD), Impulsivity, Sustained attention contour: the pattern of upward and downward changes in pitch of speech. See Pitch contrast sensitivity: visual sensitivity to varying levels of brightness. While visual acuity concerns the discrimination of stimuli with maximum contrast, contrast sensitivity has to do with the detection of visual displays that are neither maximally dark nor light. If the visual display consists of a sine wave grating pattern of alternating dark and light bars (or stripes), then it can be analyzed in terms of its spatial frequencies (i.e., the number of cycles of dark and light bars over a given region of the display). The contrast threshold is the smallest difference in spatial frequency between the dark and light bars that enables the observer to detect them. Accordingly, contrast sensitivity is 1/contrast threshold, which provides an indication of the visual system’s ability to analyze and synthesize variations in luminance, Developmental data, based on preferential looking and visual evoked potentials, points to marked improvements in both contrast sensitivity and visual acuity over the first three months after birth. It develops at a low spatial frequency to an asymptote at about 9 weeks of age, and continues to develop at high spatial frequencies until grating acuity is fully developed. See Event-related (brain) potentials (ERPs), Perceptual development, Visual acuity control group: a group of individuals who do not receive the experimental treatment being studied. This group serves as a comparison for the experimental group who do receive the treatment of interest. See Experimental method. control parameter: in dynamical systems terminology, it is not an ordering principle, but rather guides a

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system through its respective collective states (as defined by order parameters) in non-specific ways. Looked at another way, it is a boundary condition that acts as a constraint on the dynamics of the order parameter. When increased or scaled up beyond some critical value, it can transiently lose its constraining influence on the order parameter, which may then manifest stochastic or even chaotic behavior before making a sudden jump to another state. The important point about control parameters is they do not prescribe variations in the patterning of the order parameter in a strictly deterministic fashion. Instead, they control in only leading the order parameter unspecifically through regions of instabilities or keeping the system within a stable operating range. See Catastrophe theory, Chaos theory, Constraint, Determinism, Developmental bootstrapping, Dynamical systems approaches, Order parameter, Stochasticity, Synergetics controlled attention: an effortful process of attention that records the stimulus to be attended to and its neighbouring events, and whose latency depends on practice and task difficulty. See Attention conventional word: a word of the adult language, as opposed to a word created by the child. See Language development convergent evolution: the independent evolution of similar features, structures or functions in unrelated species or other taxonomic groups due to living in the same kind of environment. It often occurs due to similarity of function such as the evolution of wings in the ancestors of bats, birds and flies and which serve an analogous function (viz., flight). Similarities in structure between the shark (a fish) and the dolphin (a mammal) are a result of convergent evolution in that they evolved independently as adaptations to aquatic life. A contrast is sometimes made with parallel evolution, a term put forward by George Gaylord Simpson (1902-1984), which involves similarities due to both analogy and homology. The distinction is sometimes difficult to make. One way of doing so is to treat convergent evolution as occurring when descendants resemble each other more than was the case for their ancestors with regard to some feature, structure or function. In contrast, parallel evolution means that two or more lineages have changed in similar ways so that descendants are similar to each other as were their ancestors. Thus, for example, Australian marsupials evolved in parallel with the evolution of placental mammals in other parts of the world. See Analogy, Adaptation, Biological evolution, Homology, Lineages convergent validity: the converse of discriminant validity. An aspect of construct validity, in which measures of constructs that theoretically should be related to each other are shown, in fact, to be related to each other (i.e., you should be able to show a correspondence or convergence between similar constructs). Thus, the operationalization of a hypothetical construct should converge on other operationalizations with which it shares theoretical similarities. See Construct, Construct validity, Discriminant validity, External validity, Internal validity, Validity conversational context: a context in which two or more individuals are participating in a conversation, usually taking turns at occupying the roles of speaker and listener. Typically, such contexts are informal and loosely structured. See Communication, Context, Conversations, Reciprocity conversations: informal exchanges of feelings, observations, opinions, or ideas between two or more people. See Communication, Conversational context, Shared reference, Utterances cooing: the soft, pleasant, vocalic sounds that an infant begins to make at about three months,

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possibly indicating happiness and social communication, and an element of vocal play. See Alert wakefulness, Babbling coordination: the maintenance of a particular relationship between components of an action system. Coordination most typically refers to the timing of movement, although some authors have applied the term to describe spatial relationships as well. Interlimb coordination refers to the maintenance of a particular pattern of timing between the movements of different limbs. Intralimb coordination refers to the maintenance of a particular pattern of timing between different joints within a limb. Maintaining a relationship between the timing of a movement and the time of occurrence of a particular event in the outside environment is also a form of coordination (e.g., when catching a ball). See Action, Central patter generator (CPG), Corticospinal tract (CST), Coordinative structure, Extrapyramidal system, Integration, Motor control, Movement coordination coordinative structure: a term introduced by Nikolai A. Bernstein (1896-1966) to indicate a functional grouping of muscles spanning a number of joints that is flexibly assembled to achieve a specific goal. Also referred to as a synergy or functional generator. It is seen as a solution to the degrees-of-freedom problem in that muscles are not controlled as separate units, but as task- specific, functional groupings. See Biomechanical degrees of freedom problem, Coordination, Degrees of freedom (or Bernstein’s) problem coping: dealing with a problem; handling a problem triggered by a challenging or threatening situation actively or passively. Active or problem-focused coping involves cognitive effort to master and adverse situation, while passive or emotion-focused coping results in minimizing or avoiding the stressor. As a protective factor, successful problem-focused coping is typified by recognizing a particular situation as a source of the problem, knowing which strategies or resources to draw on, and having self-confidence in gaining control. For prelingual infants, coping can involve the ability to communicate needs and interests unambiguously by means of movement and posture, and ‘risk-taking’ behavior as expressed in being attracted by novelty and searching for challenging situations via exploration. The latter appears to be lacking, for example, in both autistic children and those with Down’s syndrome, thus placing them at risk in their cognitive development. See ‘At-risk’ concept, Protective factors, Resilience, Vulnerability copula: a linking verb whose main function is to relate other elements of clause structure, especially subject and complement, as in ‘the cup is on the table’, ‘these are hamsters’. Thus, it is the verb of existence, such as the English verb ‘be’. A zero copula, a feature of African-American English, Arabic, Hebrew, Hungarian and Russian, is when an overt copula like ‘is’ is omitted as in ‘He running’. Children’s first sentences in English contain zero copulas. Grammaticization (or grammaticalization) copying errors: refers to mistakes made when chromosomes are being replicated (e.g., deletion of certain genes or making too many copies of certain genes). They can give rise to mutations during cell division and DNA replication, and as such are one of the prime movers of genetic changes that drive evolution. Some errors such as in a gene nucleotide sequence that controls basic cell design or oxygen transport are lethal and are almost immediately ‘selected out’ so that they are not inherited by descendants. Copying errors can also be induced by environmental agents such as cigarette smoke, radiation and sunlight, but these are not passed on to descendants. Those that do occur in the DNA of cells that produce the egg and sperm, and which result in germ line mutations that give rise to hereditary diseases. See DNA,

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Genetic (or DNA) recombination, Mutation (biology), Nucleotide, Theory of natural selection cord prolapse: occurs when the umbilical cord is outside the uterus. The fetus can then crush the cord, leading to a reduction in oxygen supply from the placenta and an increased risk for brain damage. When evident, it constitutes an obstetrical emergency that requires delivery by cesarean section. See Hypoxemia, Hypoxia, Placenta core concepts: fundamental, immutable (usually physical) concepts that appear early in development and subsequently constrain the development of related concepts. See Constraint, Non-core concepts co-regulation: the idea that in face-to-face social interaction, social partners simultaneously and continuously adjust their thoughts, feelings and actions to those of their interlocutor. The concept of co-regulation implies that individuals are not autonomous in their social behavior. See Bi-directionality, Communication, Conversation Interaction, Reciprocity corpus callosum: also known as the great cerebral commissure (where a commissure is a band of fibers of tissues connecting bilateral structures), it is the large midline band or collection of commissural fibers connecting the right and left hemispheres of the cerebral cortex, with an area of about 6.2 cm2 (mid-saggital section) in the adult human. The number of fibers in the human corpus callosum has been estimated at 250,000,000. Its function is to transfer information from the cerebral cortex on one side of the brain to the same region on the other side. At about 9 weeks gestational age, the two cerebral hemispheres fuse in the midline just above the two foramina of Monro to form a commissural plate. Axons that will connect a given area of cerebral cortex on one side with the corresponding area on the other side grow into this plate, and in doing so form the corpus callosum and a smaller, separate anterior commissure. See Anterior commisure, Calcarine sulcus (or fissure), Cerebral cortex (or pallium) corrected age: postnatal age minus the number of weeks born before the gestational age of 40 weeks. For example, an infant born at 30 weeks gestation and tested at 20 weeks after birth has a corrected age of 20 ñ (40-30) = 10 weeks. This preterm infant can then be compared to fullterm infants with a postnatal age of 10 weeks. The rationale for using corrected age is that development is a function of time since conception and not time from birth. Thus, corrected age matches preterm and fullterm infants in terms of ‘level of maturity’. There is still an outgoing debate as to how long corrected age should be used and for which functions in assessing the development of preterm infants. See Chronological age, Preterm infant correspondence problem: the problem of how the imitator knows what acts of their own ‘match’ those they see in others. What is the metric of equivalence? That is a question that still has to be resolved satisfactorily in studies of imitation, and solutions may be available in comparing the kinematics of the demonstrator and the imitator. Traditional theories in cognitive psychology assume that visual and motor systems are separate; this poses the correspondence problem. See Common coding, Imitation, Kinematics, Perception-action coupling cortical area: a fundamental division of the cerebral cortex, containing many columns. Each cortical area is usually recognized by a topographic representation of some feature, like the visual field, characteristic structure of its layers, and particular inputs and outputs. See Cerebral cortex (or pallium), Cytoarchitectonic independence cortical column: a cylinder of cells extending the depth of the cerebral cortex, and which is the

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fundamental repeating unit of the cortex. Each column does a stereotyped intake, transformation and distribution of a particular class of information. See Cerebral cortex (or pallium), Motor cortex, Ocular dominance columns cortical inhibition hypothesis: associated with reflexology, it seemingly originated with the founding father of British neurology John Hughlings Jackson (1835-1911) and his idea of physiological inhibition or encephalization based on the brain possessing a hierarchical organization such that 'higher' centers (i.e., the cortex) suppressed the expression of behaviors assumed to be controlled by lower' centers (i.e., sub-cortical structures like the brain stem and spinal cord). Applied to development, it holds that earlier appearing behaviors (e.g., reflexes) are tonically inhibited by the emerging influences descending from the newly developing cortex, and in this way voluntarily-controlled actions emerge. In adult neurology, it was used by Jackson to account for the disappearance of reflexes under pathological conditions and is a reason why the hypothesis is inappropriate for the study of normal development. Other problems when applied to development, as for example by Davenport Hooker (1887-1965), include knowing the fate of the suppressed behaviors and that cortical influences are only depicted as having inhibitory functions and not excitatory ones as well. Still has its adherents in infant developmental research, but its influence is on the wane as we begin to understand better the complex and reciprocal interactions between the functions of cortical and sub-cortical structures during development. See Reflex, Reflexology, Stepping response cortical lobes: the following table summarizes the Brodmann area (number), the location and other names associated with the four lobes. See Cerebral cortex (or pallium), Cerebral cortex (functions) Lobe Number Location Other names 4 Precentral gyrus, paracentral gyrus Primary motor area Premotor area, Superior & middle frontal gyri, 6 supplementary motor precentral gyrus Frontal area 8 Superior & middle gyri Frontal eye field Opercular & triangular parts of 44, 45 Broca’s area inferior frontal gyrus 17 Banks of calcarine sulcus Primary visual area; VI Occipital Visual association area; 18, 19 Surrounding 17 V2, V3, V4, V5 Postcentral gyrus, paracentral Primary somatosensory 3, 1, 2 lobule association area; S1 Somatosensory Parietal 5, 7 Superior parietal lobule association area 39 Inferior parietal lobule Angular gyrus 40 Inferior parietal lobule Supramarginal gyrus 41 Superior temporal gyrus Primary auditory area Auditory association Temporal 42 Superior temporal gyrus area 22 Superior temporal gyrus Wernicke’s area

cortical plate: the term for the developing cortex in embryogenesis, before it contains all its cellular

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components and has differentiated into its mature structure. See Cajal-Retzius cells, Cerebral cortex (development), Embryogenesis corticopspinal tract (CST): also known as the pyramidal tract or system, it is a descending tract from layer 5 of the cortex containing the axons from neurons in the primary and secondary motor cortex and somatosensory cortex to nuclei in the brain stem, and to motoneurons and interneurons in the spinal cord. It passes through the internal capsule, decussates in the pyramids (75-80% cross), with about 80% of axons becoming the lateral corticospinal tract and 20% the ventral corticospinal tract. The axons terminate onto internuncial neurons or alpha motoneurons of the ventral horn. These tracts control fine movements, and their destruction leads to reduced dexterity of the hands and fingers, and some loss of muscle tone. There is no effect, however, on posture or on the use of limbs for reaching. The functional development of the CST in humans is still not completely understood, with some claiming functionality already in the newborn based on transcranial magnetic stimulation. See Alpha (α) motoneurons, Direct corticomotoneuronal connections or tracts, Extrapyramidal system, Internal capsule, Interneurons, Motoneuron, Spinal cord, Transcranial magnetic stimulation (TMS), Ventral horn corticosteroids: hormones with anti-inflammatory properties, and involved in responses to stress, that are produced by the adrenal cortex of the kidneys through being synthesized from cholesterol. See Adrenal cortex, Adrenal gland, Cholesterol, Hormones, Steroid hormones cortisol: a hormone, the primary glucocortoid, secreted by the adrenal cortex glands in response to any kind of physical or psychological stress. Cortisol has a fundamental role in metabolism and is essential in maintaining normal physiological functions in the liver, heart and lungs kidneys, the immune system and the brain. Low or high levels can result in functional impairments in one or more of these systems. See Adrenal cortex, Adrenal gland, Cholesterol, Hormones, Metabolism count noun: a noun that refers to a discrete object, as opposed to some general substance or mass. See General nominals, Proper noun counter-suggestion: a comment or question that challenges a participant’s answer by highlighting a potential contradiction. Counter-suggestions are commonly used in Piagetian clinical interviews and are designed to counteract the possible suggestive influence of a previous question. See Closed-end interviewing covariance: the expectancy of the cross-product of the differences of two strings of random scores from their respective means. Weighting by the strings’ respective standard deviations yields the correlation of the two strings. Thus, it is the summary statistic of association among a pair of variables calculated as the average of the products of the deviations of each variable. See Pattern of variances and covariances, Variance-covariance matrix covert attention: discovered by Hermann von Helmholtz (1821-1894), discussed at length by Wiiliam James (1842-1910) in his Principles of psychology (1890) and subsequently contrasted with overt attention, it is the selection of targets in the absence of actual eye movements, and thus without any fixation shift to a cued location (e.g., when ‘looking out of the corner of one’s eye’, ‘keeping half eye on’, every day terms that are better labeled as ‘peripheral and mental focus’). Covert attention improves discriminability in many visual tasks such as contrast sensitivity, texture segmentation, and visual search. It also appears to speed up the rate at which

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information is processed through enabling the observer to exclude task-irrelevant information. Changes in gaze (i.e., overt attention) require shifts in covert attention, and the latter involves disengagement of attention from a stimulus or locus and inhibition of return (a bias against reorienting attention to a previously cued location). Evidence suggests that the covert attention system becomes functional during the first six months of life, with it rapidly achieving greater consistency and flexibility after the third month. See Attention, Contrast sensitivity, Overt attention cranial nerve: twelve motor and sensory peripheral nerves emerging from the brains of vertebrates that carry the special senses, and control certain movements in the upper body, the nuclei of which reside in the brain stem (i.e., they arise in the brain stem), except for the olfactory and optic nerves. These nerves are distinct from spinal nerves that emerge from the spinal cord. They are identified with Roman numerals, and each has functions that are motor, sensory or both (see table below). See Auditory (or acoustic) nerve, Brain stem, Peripheral nervous system (PNS), Vagus (or pneumogastric) nerve

Cranial nerve Roman number Functions Sensory: olfaction, conducting impulses from mucous Olfactory nerve I membranes of nose to olfactory bulb Sensory: vision, arising from retina and carrying visual information to Optic nerve* II thalamus and other parts of brain (e.g., primary visual cortex) Motor: control of eye movements through innervation of 4 of 6 Oculomotor nerve III extrinsic eye muscles and pupil size via sphincter muscle Motor: involved in eye movements Trochlear (or ‘pathetic’) IV through innervation of superior nerve oblique eye muscles Both: registering sensations on the face, in the mouth, and control Trigeminal (or trifacial) of chewing movements. Divided V nerve into three branches: optic (orbits), mandibular (lower jaw) and maximillary (upper jaw) nerves Motor: eye movements through Abducens (or abducent) innervation of posterior rectus eye VI nerve muscles that rotate eyes toward nose and turns them downward Both: movement of facial and inner ear muscles and gustation Facial nerve VII (taste buds on front part of tongue) Sensory: hearing and balance, Vestibulocochlear (or supplying hair cells of cochlea via VIII acoustic) nerve the cochlear nerve and vestibular system via the vestibular nerve to

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the semicircular canals Both: gustation, receives fibers from back of tongue, the tonsils Glossopharyngeal nerve IX and pharynx, and supplies fibers to the pharynegeal muscles, being also responsible for the gag reflex Vagus (or pneumogastric) Both: gustation, speech, X nerve swallowing Motor: movement of shoulders Accessory (or spinal XI and neck, accessory to vagus accessory) nerve nerve Motor: movement of tongue, Hypoglossal nerve XII supplies intrinsic muscles of tongue * Unlike other cranial nerves is in the central nervous system, not the peripheral nervous system

Cranial nerves: each one is given a Roman numeral, together with whether they are motor, sensory or both, and their functions. Some cranial nerves contribute to the same function. An aid to remembering whether each cranial nerve is motor (M), sensory (S) or both (B) is the mnemonic “Some Say Money Matters But My Brother Says Big Biceps Matter Most”. Another mnemonic enables one to remember their order of emergence from cranial to more caudal through openings in the skull: “Oh Once One Takes The Anatomy Final Very Good Vacations Are Heavenly”. crawling: a form of locomotion in which the torso is parallel to the ground and the four limbs are used for propulsion. At the start of crawling, weight is equally distributed across all four limbs in a posture such that the arms are extended downward from the shoulder at shoulder width, palms on the floor with the fingers pointing forward, thighs are vertical and hip-width apart, and the knees are on the floor with lower legs and feet pointing backward. When crawling forward, the arms and thighs move parallel to the body midline, the legs flex alternately, and the arm and leg on the opposite side of the body move simultaneously. Most infants, however, hardly ever comply with all details of this two-part description as there is considerable individual variation in both the starting posture and the subsequent pattern of interlimb coordination. As a motor milestone, crawling is typically preceded by creeping during which both arms are extended, and both legs flex symmetrically, initially with the stomach on the supporting surface. Some infants, however, start crawling without ever having had experience with creeping. See Coordination, Cruising, Locomotion, Motor milestone creatine: an amino acid derivative that does not occur in proteins but is found in cardiac and skeletal (or striated) muscle tissue, it is a nitrogenous compound that stores energy for muscle contraction when phosphorylated. See Amino acids, Adenosine triphosphosphate (ATP), Cardiac muscle, Phosphorylation, Proteins, Striated (or striped or voluntary) muscle creativity: thinking of or acting out new and unusual ways of expression or of solving a problem, as opposed to repeating what has previously been observed or learnt from instruction. It also involves identifying a previously unrecognized problem (i.e., problem finding instead of problem solving) See Heuristics, Problem solving critical literacy: a way of teaching literacy that emphasizes looking at the meanings embedded within texts and making explicit the author’s purpose in writing the text in a particular way. Teaching

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entails questioning the construction of texts and analyzing the power of language to convey different things to different people. Students are encouraged to reflect on their own and others’ attitudes and values. See Literacy, Vernacular (or community) literacies critical period: a concept originating in embryology that referred to a time in development or growth that was most susceptible to the induction of new structures by neurochemical agents and whose effects were considered to be irreversible. Today, the term ‘sensitive period’ is generally used and applied to the development of both structure and function (e.g., learning). See Induction, Sensitive period

Cronbach’s alpha: a coefficient of internal consistency (and strictly speaking, not a statistical test) that measures the degree to which item responses obtained on some test or instrument at the same time correlate with each other. Technically, it is the mean intercorrelation for all possible item pairs weighted by variances, and taking into account the number of items such that the value obtained ranges from 0 (zero internal consistency) to 1 (perfect internal consistency). As with Cohen’s kappa coefficient, there is no test to adjudicate whether an alpha value is significant. It is, however, commonly accepted that an alpha of 0.70 or higher is acceptable, perhaps because 0.70 indicates that the standard error of measurement will be over half a standard deviation. Alpha is not only a function of the mean intercorrelation, but also of the number of items. Thus, as the number of items is increased, alpha becomes larger, even if the intercorrelations between items are relatively low. Also, it will be higher when within-subject responses are more consistent, interindividual variability is higher, and when there is homogeneity of variances among items. Under some circumstances, alpha may be negative, which reflects a serious coding in coding the data, and thus the need to recode them to ensure that all items are coded in the same direction. When computed for binary (e.g., yes/no) items, Cronbach’s alpha is identical to the Kuder-Richardson-20 formula for composite scales. The coefficient was devised by Lee Cronbach (1916-2001) in 1951 based on the work of Louis Guttman (1916-1987). The formula for the coefficient is given below See Cohen’s kappa coefficient, Composite (or sum) scale, Internal consistency N .r a = 1+(N -1).r where N = number of items, r = meaninter - item correlationamong items cross-cultural psychology: a methodological approach to the study of the relationships among (human) behavior and cultural context. It is an important methodology for testing the universality of human behavior and development, perhaps its main aim. There are two other aims: to discover variations in behavior and development that are not present in one’s own culture, and to integrate the first two aims in order to generate a more universal psychology. See Back- translation, Bias (cultural), Comparative method, Context, Culture, Equivalence (of data across cultures), Relativism, Torres Straits expedition, Universalism (or cultural relativism) cross-lagged correlation/regression model: a statistical technique used in longitudinal research in which the relative influences of two variables upon one another are examined, while the correlations between each within time and within each across time are taken into account. More technically, it is a linear regression model where scores on at least two variables (X and Y) are measured on at least two occasions (t=1 and 2) and the scores at the later occasion (X[t+1]) are predicted by the same variable ‘lagged’ in time (X[t]) and the other variable ‘crossed’ in time (Y[t+1]). See Longitudinal design

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cross-modal coordination: coordination of information that is picked up by different sensory modalities. For example, cross-modal coordination allows humans to recognize that a person’s face (visual modality) and voice (auditory modality) go together. There are cross-modal connections among all five sensory modalities (sight, sound, smell, taste, and touch). See Active intermodal matching, Cross-modal matching, Intermodal coordination cross-modal matching: the integration of information from different perceptual systems (e.g., the mapping of visuo-spatial coordinates onto proprioceptive information about the position of the body in space). See Active intermodal matching, Cross-modal coordination, Intermodal coordination, Proprioception cross-sectional design: a study that cuts across a population to compare different groups. It may compare the sexes or different social groups, but usually is used to compare different age groups. See Cohort, Cohort effect, Longitudinal design, Longitudinal studies cruising: a locomotor milestone in which the infant walks sideways with support. See Crawling, Locomotion, Walking crying: vocal, facial and bodily behaviors that are often interpreted as signs of distress, and which in early infancy is often accompanied by characteristic patterns of movement and posture. An interesting, and as yet unresolved issue, is whether the non-vocal components of crying (e.g., facial movements) develop prenatally in the human. See Colic, Crying peak, Fussing, Larynx, Pharynx, Posture, Vagus (or pneumogastric) nerve

crying peak: epidemiological studies, carried out mainly in Western societies, have found a peak in minutes of infant crying per 24 hours at around 5-6 weeks of age. However, the same phenomenon has also been found in non-Western cultures and in preterm infants of the same corrected age, which suggest it is a universal feature of early infancy. See Colic, Crying crystallized intelligence: the ability to use knowledge and problem-solving methods acquired through learning and experience to resolve a current problem. It has been argued that the Scholastic Aptitude Test assesses crystallized intelligence as do the verbal sub-tests of IQ batteries. Based on factor analysis, it was part of a theory of intelligence put forward by Raymond B. Cattell (1905-1998) in 1971 that separated the ‘g’ factor of Charles E. Spearman (1863-1945) into crystallized and fluid intelligence. As an addendum to his theory, Cattell also proposed what he called investment theory: how fluid intelligence might contribute to crystallized intelligence, but not the other way round. See ‘g’, Factor analysis, Fluid intelligence, Flynn effect, Intelligence, Progress, Scholastic Aptitude Test (SAT) culture: partially overlapping systems of artifacts (e.g., social institutions, technology), meanings, practices and symbols (e.g., derived from myths) that are distributed throughout a given linguistic community, and which guide the shared life of individuals in different groups. Language and sign systems play a central role in representing the meanings that are distributed throughout a culture. See Anthropology, Context (cultural), Cross-cultural psychology, Representation (cultural), Signs, Symbols cultural evolution: the transmission of behaviors broadly defined between generations through the mechanisms of instruction, teaching, observational learning, imitation and their combinations, resulting in the accumulation of knowledge and traditions reflected, for example, in child-rearing

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practices. Thus, unlike biological evolution, it abides by Lamarckian principles. Transmission can occur vertically (from parent to offspring), horizontally (between members of the same age group or generation) and obliquely (from non-parental members of the parental generation to offspring). Innovative or accidental changes in the content of these transmissions can result in cultural change or cultural evolution. What is sometimes overlooked is that the pathways of transmission can be reversed such that the offspring are the transmitting source. The best- known example of this pathway of cultural evolution concerns the free-ranging Japanese macaque monkeys of Koshima Island who were first studied in the 1950s. When sweet potatoes were scattered on the beach, the troop moved out of its forest habitat. In the new habitat, a 1.5 year-old female (Imo) invented the act of potato washing in fresh water then later in the sea. This act was initially imitated by her playmates and much later by adults older than 12 years. When Imo’s playmates became mothers themselves, they ensured that potato washing became a tradition through encouraging their infants to imitate them. There are other examples the same phenomenon in Japanese macaques (e.g., caramel eating that was first accepted by those under 3 years of age and then propagated through the dominance hierarchy, first with the mother and then with sub-leaders and leaders of the troop). These, and other primate studies, raise the issue of whether culture and cultural evolution are restricted to humans. Other issues have concerned whether cultural evolution is unilinear or multilinear and involves progress, to what extent it is analogous to biological evolution (e.g., is there such a thing as cultural selection?) or whether they interact in some way, and what is the unit of transmission (one of the most recent examples being the meme concept). See Biological evolution, Cultural selection, Cultural evolution and biological evolution, Culture, Lamarckism, Meme, Progress cultural evolution and biological evolution: the theoretical stance adopted in sociobiology and its successor evolutionary psychology that biological and cultural evolution co-evolve, a sort of Darwinian theory of culture, and termed a ‘feedback reciprocal relation’ by Theodosius Dobzhansky (1900-1975). Accordingly, there is a direct co-evolutionary relationship between genes and culture such that changes in one can lead to changes in the other. An alternative view is that the relationship is indirect: biological and cultural evolution are interacting, but potentially independent, processes that result in human phenotypes evolving in the direction of states that maximize inclusive fitness. As a consequence, cultural evolution has the property of emergent novelty that cannot be reduced to the action of genes. It is important to point out that the term ‘co-evolution’ has another connotation in evolutionary biology. See Biological evolution, Co-evolution, Cultural evolution, Cultural selection, Emergence, Inclusive fitness cultural selection: the claim that culturally-determined selection pressures can act on human gene frequencies to create biological changes. Two examples offered are lactose tolerance and the ability to metabolize alcohol, both seemingly having arisen rapidly and recently to create divergent evolution in humans. Such downward causation has been challenged by those who prefer to interpret these examples in terms of the founder effect and random genetic drift (e.g., lactose tolerance may have occurred in those cultures where the relevant genes were already fortuitously present). See Alcohol tolerance, Cultural evolution, Cultural evolution and biological evolution, Downward causation, Founder effect, Genetic drift (or random walk), Lactose tolerance cumulative incidence (CI): the proportion of people who become diseased during a specified period of time and calculated as:

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CI = number of new cases of a disease during a given period of time/total population at risk

An even more precise estimate of incidence that utilizes all available information is called the incidence rate (IR), force of morbidity or mortality, or incidence density (ID). This is considered to be a measure of the instantaneous rate of development of disease in a population and is defined as:

ID = number of new cases of a disease during a given time period/total person-time of observation See Epidemiology, Odds ratio cybernetics: although a term first used in French (‘cybernetique’) by Andrè M. Ampére (1775-1836), it is generally credited to Norman Weiner (1894-1964) who derived it in 1947 from the Greek word for ‘steersman’ to denote the study of communication, feedback, and control mechanisms in living systems and machines. Subsequently developed together with Arturo Rosenblueth (1900-1950), Julian Bigelow (1913-2003) and William Ross Ashby (1903-1977), it drew originally on electrical engineering and the Shannon-Weaver information theory, but also on mathematics, biology, neurophysiology, anthropology, and psychology to study and describe actions, feedback, and response in systems of all kinds. Known as first-order cybernetics, its earliest applications were to designing control mechanisms for physical (i.e., closed) systems (e.g., aiming of artillery weapons) based on circular causality (i.e., negative feedback and the maintenance of homeostasis). This approach was followed by second-order cybernetics or applied cybernetics that can be defined as a theory of the observer based on functional- constructivism (i.e., with how observers are part of the systems that they have constructed and with which they interact) and that emphasizes the role of positive feedback in open systems in that process. More recently, third-order cybernetics, building on social constructivism, has appeared that involves studying how observers and systems co-evolve across different social systems. Even more recently, there has been a claim for fourth-order cybernetics that seems to concerned with how multiple realities are shaped by social, cultural, economic, ethnic, gender and disability values impinge upon power relationships within society. All told, cybernetics, which is a prime example of an interdiscipline, has had a major influence across a very wide range of the natural and social sciences, including anthropology, cognitive science, computer science, connectionist modeling, and the study of motor control. See Artifical intelligence (AI), Circular causality, Closed system, Closed-loop and open-loop control, Computational models, Connectionist models, Constructivism, Entropy, Feedback, Interdiscipline, Motor control, Open system cytoarchitectonic independence: refers to the anatomical and cellular orthogonality of different brain regions. See Cortical area, Modularity cytokines: any of numerous hormone-like, low-molecular-weight proteins, chemically identified as purines, secreted by various cell types that regulate the intensity and duration of immune response and mediate cell-cell communication, as well as acting as signals in cell survival, growth, differentiation and apoptosis. Examples include interferon, interleukin, lymphokine, chemokines and various growth factors. See Apoptosis, Differentiation (embryology), Fibroblast growth factor, Proteins, Purines cytoplasm: the jelly-like material (protoplasm) surrounding the nucleus of a cell containing fibrous elements consisting of the Golgi apparatus, microtubles, action microfilament, and intermediate filaments. These self-propagating entities can be inherited in a non-Mendelian mode

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(cytoplasmic inheritance). It is differentiated into ectoplasm (concerned mainly with cell movement) and less dense endoplasm containing most of the cell’s structures. The cytoskeleton provides structural support for the cell and permits directed movements of organelles, chromosomes, and the cell itself. See Cell, Cytoskeleton, Golgi apparatus (or complex or organ), Inheritance, Mendelian genetics, Organelle cytosine: a pyrimidine base found in DNA and RNA, as well as nucleotides and their derivatives. It always bonds with the purine guanine. See DNA, Guanine, Nucleotide, Purine, Pyrimidines, RNA cytoskeleton: the internal framework (or ‘scaffolding’) of a cell within the cytoplasm, composed largely of actin filaments and microtubules. In eurayotic cells, actin filaments (or microfilaments) are active in muscle contraction, intermediate filaments hold microfilaments and microtubules in place, and microtubules serve as routes for organelles to move along. In general, the cytoskeleton helps to maintain the shape of the cell, enables the intracellular transport of organelles like mitochondria and vesicles (using structures such as flagella and cilia), and plays a key role in cell division. See Actin, Cell, Cytoplasm, Euraykote, Flagella, Mitochondria. Mitosis, Organelle, Vesicles

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