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University Microfilms International 300 N. ZEEB ROAD, ANN ARBOR, Ml 48106 18 BEDFORD ROW, LONDON WC1R 4EJ, ENGLAND 8015933
V r a n e k o v i c, G e o r g e Jo s e p h
CARDIAC RESPONSIVITY AND NON-NUTRITIVE SUCKING PATTERNS OF FULL TERM, PREMATURE, AND HIGH RISK INFANTS
The Ohio State University PH.D. 1980
University Microfilms I n t e r n a t i o n a l 300 N. Zeeb Road, Ann Arbor, MI 48106 18 Bedford Row, London WC1R 4EJ, England
Copyright 1980 by Vranekovic, George Joseph All Rights Reserved CARDIAC RESPONSIVITY AND NON-NUTRITIVE SUCKING PATTERNS
OF FULL TERM, PREMATURE, AND HIGH RISK INFANTS
DISSERTATION
Presented in Partial Fulfillment of the Requirements for
the Degree Doctor of Philosophy in the Graduate
School of The Ohio State University
By
George Joseph Vranekovic, B.A., M.A.
*****
The Ohio State University
1980
Reading Committee: Approved By
Dr. Henry Leland
Dr. Phil Clark
Dr. Barbara Edmonson Depart ipdnt of Psychology ACKNOWLEDGEMENTS
When looking back over four years of graduate education, a stu dent realizes that certain individuals have been instrumental in shaping both his interests and philosophy. The first of those that come to mind is Dr. Donald Smith, my former adviser, who encouraged me in the early days of my graduate career, and led me to my initial contacts with the area of this particular study. Also included are those outstanding members of the Department of Psychology at The
Ohio State University, such as Dr. George Thompson, Dr. Charles Wenar,
Dr. Phil Clark, and Dr. Barbara Edmonson. The utmost thanks must go to my present adviser, Dr. Henry Leland, who has not only encouraged, guided, and supported my various research efforts, but also shown patience, interest, and acceptance of those projects.
The two individuals who are most responsible for the completion of this dissertation and other related work are Dr. Leandro Cordero and Dr. Ellen Hock. Dr. Cordero's support of psychophysiological research has enabled me to enjoy a cordial, accepting atmosphere among the personnel of the University Hospital's Department of Pedi atrics and Neonatology. It was Dr. Hock who initiated the contact between the Department of Psychology and University Hospital, and completed the first of a series of heart rate studies, thus making it possible to garner the interdisciplinary support needed for such an effort. ii A note of appreciation is in order for Dr. Paul Isaac's assist ance in the analysis of the data, a task which involved reducing an unbelievable mass of data into something meaningful and understand able.
I cannot fail to mention those who, at certain stages, assisted in the collection and tedious analysis of the data: Chris Harter and
Patrice McCarthy, two nurses who were invaluable in their care and handling of the newborns during most of the procedures; Linda Knight, who was a constant help in my absence; and Dottie Turner, a knowl- edgable nurse who was always available when needed.
Finally, to the nurses and staff of both the Newborn Nurseries and Neonatal Intensive Care Unit of The Ohio State University Hospi tal, my deepest thanks for the patience they showed while a strug gling student constantly wandered through their wards. VITA
November 28, 1948 ...... Born - Cleveland, Ohio
1970...... B.A., University of Miami, Coral Gables, Florida
1970-1971 ...... University Fellow, Department of Psychology, The Ohio State University, Columbus, Ohio
1971-1972 ...... Teaching Assistant, Department of Psychology, The Ohio State University, Columbus, Ohio
1972...... M.A., The Ohio State University, Columbus, Ohio
1972-1973 ...... Research Assistant, Department of Pediatrics, University Hospital, The Ohio State University, Columbus, Ohio
1973-1974 ...... Dissertation Fellow, Department of Psychology, The Ohio State University, Columbus, Ohio
1974-1976 ...... Psychology Intern, Parsons State Hospital and Training Center, Parsons, Kansas
1976-1980 ...... Staff Psychologist, Parsons State Hospital and Training Center, Parsons, Kansas
PUBLICATIONS
"Heart Rate Variability and Cardiac Response to an Auditory Stimulus." Biology of the Neonate, 1974, 24, 66-73.
iv FIELDS OF STUDY
Major Fields: Developmental Psychology and Developmental Disabili ties
Studies in the Psychology of the Exceptional Child and Adult. Professors Henry Leland and Barbara Edmonson.
Studies in Developmental Assessment and Psychological Test Con struction. Professors Donald Smith and Donald Bersoff.
Studies in Social and Cognitive Development. Professor George Thompson.
Studies in the Neuropsychological Aspects of Infant, Childhood, and Adult Behavior. Professors Donald Meyer, Ellen Hock, Charles Wenar, and Leandro Cordero.
v TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS...... ii
VITA ...... iv
FIELDS OF STUDY ...... v
LIST OF T A B L E S ...... viii
LIST OF F I G U R E S ...... x
Chapter
I . INTRODUCTION ...... 1
II. REVIEW OF THE L I T E R A T U R E ...... 6
Determinants of the Cardiac Response to Stimulation . . . 6 Theories of the Cardiac Response to Stimulation ...... 14 The Development of Resting Heart Rate and Its Variability...... 18 Developmental Studies of the Cardiac Response to Stimulation...... 23 Sucking Behavior in the Human Infant ...... 29
III. METHODOLOGY...... 38
Subject Characteristics ...... 38 Experimental Procedures ...... 40 Methodological Issues ...... 47
IV. ANALYSIS OF THE D A T A ...... 50
Reduction and Analysis of the Heart Rate D a t a ...... 50 Preparation and Analysis of the Sucking D a t a ...... 54
V. R E S U L T S ...... 57
Analysis of Group Differences on the Auditory Cardiac D a t a ...... 57
vi Page
Analysis of Group Differences on the Tactile Cardiac D a t a ...... 60 Correlational Analyses on the Auditory and Tactile Cardiac D a t a ...... 63 Analysis of Responsivity Change Over Trials...... 64 Analysis of Group Differences and the Correlational Analysis on the Non-Nutritive Sucking Data ...... 65 Stepwise Regression Analysis on the Cardiac and Non-Nutritive Sucking Data ...... 67 Correlational Analyses Relating the Cardiac and Sucking D a t a ...... 69
VI. DISCUSSION...... 106
VII. SUMMARY...... 116
BIBLIOGRAPHY...... 121
vii LIST OF TABLES
Table Page
1. Subject Characteristics - Healthy Full Term Infants. . . 41 2. Subject Characteristics - Premature Infants...... 42 3. Subject Characteristics - High Risk Full Term Infants...... 43 4. Healthy Full Term Males - Average Cardiac Response - Auditory Modality ...... 71 5. Healthy Full Term Females - Average Cardiac Response - Auditory Modality ...... 72 6 . Premature Males - Average Cardiac Response - Auditory Modality ...... 73 7. Premature Females - Average Cardiac Response - Auditory Modality ...... 74 8 . High Risk Full Term Males - Average Cardiac Response - Auditory Modality ...... 75 9. High Risk Full Term Females - Average Cardiac Response - Auditory Modal i t y...... 76 10. Summary of One-Way Anovas Across the Groups for the Auditory Cardiac D a t a ...... 77 11. Post-Hoc Tests for Significance for One-Way Anovas Across the Groups ...... 78 12. Summary of Analysis of Covariance Across the Groups for the Auditory Cardiac D a t a ...... 79 13. Healthy Full Term Males - Average Cardiac Response - Tactile Modality ...... 80 14. Healthy Full Term Females - Average Cardiac Response - Tactile M o d a l i t y ...... 81 15. Premature Males - Average Cardiac Response - Tactile Modality...... 82 16. Premature Females - Average Cardiac Response - Tactile Modality ...... 83 17. High Risk Full Term Males - Average Cardiac Response - Tactile Modality ...... 84 18. High Risk Full Term Females - Average Cardiac Response - Tactile Modality ...... 85 19. Summary of One-Way Anovas Across the Groups for the Tactile Cardiac D a t a ...... 86 20. Post-Hoc Tests of Significance for One-Way Anovas Across the Groups on Tactile Cardiac Data .... 87 21. Summary of Analysis of Covariance Across the Groups for the Tactile Cardiac D a t a ...... 88 viii Table Page
22. Correlation Matrix Across All Sixty Infants for Auditory Cardiac Data ...... 89 23. Correlation Matrix Across Sixty Infants for Tactile Cardiac D a t a ...... 90 24. Summary of One-Way Anovas Over Eight Trials for the Auditory Cardiac D a t a ...... 91 25. Summary of One-Way Anovas Over Eight Trials for the Tactile Cardiac D a t a ...... 92 26. Healthy Full Term Males - Average Performance - Non-Nutritive Sucking ...... 93 27. Healthy Full Term Females - Average Performance - Non-Nutritive Sucking ...... 94 28. Premature Males - Average Performance - Non-Nutritive Sucking ...... 95 29. Premature Females - Average Performance - Non-Nutritive Sucking ...... 96 30. High Risk Full Term Males - Average Performance - Non-Nutritive Sucking ...... 97 31. High Risk Rull Term Females - Average Performance - Non-Nutritive Sucking ...... 98 32. Summary of Analysis of Variance Across the Groups for the Non-Nutritive Sucking D a t a ...... 99 33. Correlation Matrix Across All Sixty Infants for Non-Nutritive Sucking D a t a ...... 100 34. Summary Table of Stepwise Regression Analysis for the Auditory Cardiac D a t a ...... 101 35. Summary Table of Stepwise Regression Analysis for the Tactile Cardiac Da t a ...... 102 36. Summary Table of Stepwise Regression Analysis for the Non-Nutritive Sucking D a t a ...... 103 37. Correlation Matrix Across All Sixty Infants Relating Auditory Cardiac Data and Non-Nutritive Sucking D a t a ...... 104 38. Correlation Matrix Across All Sixty Infants Relating Tactile Cardiac Data and Non-Nutritive Sucking D a t a ...... 105
ix LIST OF FIGURES
Figure Page
1. Sample Consent F o r m ...... 44
2. Sample Printouts Demonstrating Cardio- tachometer and Sucking Data for Selected Infants...... ] j3
3. Sample Printouts Demonstrating Cardio- tachometer and Sucking Data for Selected Infants...... ] 14
4. Sample Printouts Demonstrating Cardio- tachometer and Sucking Data for Selected Infants j 15
x CHAPTER I
INTRODUCTION
Developmental research has shown an increased interest in consid ering human behavior in very early infancy, during the first few days of life. Studies in cardiac responsivity to stimulation have attempted to define certain physiological correlates of attention and information processing, possibly enabling one to differentiate groups of infants on the basis of their reactions to stimuli. Research using sucking be havior as the parameter of interest has advanced to the point where groups of infants have been differentiated on the basis of their suck ing patterns. One major differentiation in both cardiac and sucking response studies has been made between groups of healthy and depressed infants, with significant differences being found in both parameters.
With the availability of extensive information on perinatal circum stances at The Ohio State University Hospital, an opportunity to con struct well-defined groups of infants exists, and a study considering the cardiac and sucking responses in these groups, how they differen tiate the groups, and how they relate to one another could be very definitive.
In recent years a considerable amount of research has been done using the cardiac response to stimulation as a measure of attention. In attempting to relate internal neurological activity to the process
of encoding information, this research has shown that deceleration is
the major cardiac response to the intake of visual and auditory stim
uli for the adult and the young child. For the neonate, however, the
findings are often contradictory, probably due to such variables as
the state of the neonate, type and intensity of stimuli used, and the
manner in which the data is analyzed. The study by Hock (1971) sup
ported the notion (Graham and Jackson, 1970) that the cardiac response
to auditory and tactile stimulation in the neonate is consistently ac-
celeratory.
Studies by John Lacey (1959, 1964) and Michael Lewis et al.
(1965, 1966, 1967, 1968, 1969) have supported the belief that cardiac
deceleration occurs during the intake of stimulation, and that accel eration occurs during the rejection of stimulation or during problem
solving. Also supported in these studies is the idea of a develop mental trend, with older infants showing greater deceleration than the younger ones, a phenomenon possibly due to the effects of neurological maturation. Steinschneider (1971) and Ashton (1973) have noted that the cardiac response is a function of several variables, such as prop erties of the stimulus involved, state and stage of development of the subject, individual differences, and the level of organ functioning prior to stimulation. One aspect of the prestimulus level of func tioning which has until recently (Porges 1973, 1974) been relatively ignored is the variability (often called irregularity) of the resting heart rate. Hon (1968) has considered irregularity a healthy sign, indicating that the fetus or the newborn has a functioning, well developed nervous mechanism for controlling its heart rate. He states
further that one aspect of the heart rate which has not received ade
quate attention is the absence of irregularity, a baseline heart rate which is fixed or smooth. This type of pattern is said to indicate that the nervous control mechanisms of the heart are not fully devel oped or have been altered by drugs or hypoxia. Infants with such flat heart rate patterns have been shown to be depressed in their re- sponsivity to various stimulation, thus indicating a diminished sen sitivity to certain inputs. The level of resting heart rate vari ability and its relationship to the degree of responsivity will be considered for all groups of infants in this study.
Also of importance in cardiac studies is the measure of habitu ation, the degree to which either the acceleratory or deceleratory responses tend to decrease with repeated stimulation. This is seen as evidence of early learning, learning not to respond to certain stimuli, and is considered to be dependent on a healthy, mature neu rological condition. The rate of this habituation depends on the type of stimulation used (auditory, tactile, visual), the sense modality involved, individual differences, and the infant's condition. There fore, habituation may not occur, or may occur at a slower rate, in an immature or depressed group of infants for certain modes of stimuli, as has been suggested in previous studies (Stamps, 1980; Adkinson and
Berg, 1976; Rose, Schmidt, and Bridger, 1976). It may also hold that individual differences will predict later development in the cognitive skills area, with rapid habituators seen as efficient learners through out later life (Miller, Ryan, Short, Ries, McQuire, and Culler, 1977). This possibility needs to be considered further through longitudinal study.
One portion of this study will be concerned with the phenomenon of habituation, its presence as an indication of early learning, and the possibility of differential rates of habituation between groups of infants. Two major theoretical viewpoints accounting for habitu ation are those of Sokolov (1963) and Hebb (1949). Both theories propose the formation of integrated circuits in the nervous system,
"neuronal models" or "cell assemblies," which amount to neurological models that are developed with repeated exposure to a stimulus. Once this model is formed, exposure to the stimulus involved may no longer trigger the internal arousal that accompanies novel stimuli. Impor tant to this study is the emphasis in both theories that the more mature and intact the central nervous system of the organism, the faster the model is formed and the sooner an arousal response should diminish.
A considerable amount of research has been done using sucking responses as the parameter of interest. The non-nutritive mode has been regarded as a reflex motor behavior, distinct from the nutritive mode only in the human species (Wolff, 1968; Shirataki, 1973), which matures as a function of gestational or chronological age, and is relatively unaffected by experience (Dubignon, Campbell, and Parting ton, 1969). Studies by Kaye (1966), Sameroff (1966), and Kessen
(1967) have defined the response in operational terms, shown certain aspects of its morphology, and considered its use as a conditioned response. Studies such as that of Kron, Ipsen, and Goddard (1968) have shown consistent individual differences between infants during
repeated tests of sucking behavior, indicating the worth of employing
sucking responses as an expression of individuality early in life.
While sucking is considered to be organized at a relatively primitive
level of the nervous system, studies by Wolff (1968), Dreier and
Wolff (1972), and Kron, Stein, and Goddard (1966) have shown that, when measured quantitatively, groups of infants with certain patho
logical conditions show significant differences in their patterns of
non-nutritive sucking. This study will consider the non-nutritive
sucking patterns of several groups of infants, looking for signifi
cant differences in those patterns. These indicators will be viewed
in conjunction with the cardiac data in an attempt to show agreement between the two sets of data as an indication of neurological in volvement .
Hypotheses to be considered are as follows:
1. That differences exist between the groups with respect
to the degree of responsivity and habituation of the
cardiac response corresponding to the mode of stimulation
and the sense modality considered.
2. That differences exist between the groups relative to the
various measures of the sucking response.
3. That differences in the cardiac data will correlate with
differences in the sucking data as indicators of neuro
logical involvement or immaturity. CHAPTER II
REVIEW OF THE LITERATURE
This chapter is divided into five sections, covering in succes
sion studies concerned with: the determinants of the cardiac response
to stimulation, theories of the cardiac response to stimulation, the development of resting heart rate and its variability, developmental
studies of the cardiac response to stimulation, and finally sucking behavior in the human infant.
DETERMINANTS OF THE CARDIAC RESPONSE TO STIMULATION
The cardiac response to stimulation is not a clean, knee-jerk type of response which exists in an all-or-none fashion. The response which is elicited is dependent upon organismic, procedural, and stim ulatory variables. Steinschneider (1971) has addressed himself to these facts and summarized that the response is dependent upon the organism's level of functioning prior to stimulation, the properties of the stimulus involved, the unique individual differences of each subject, and the state and stage of development of the subject. Ashton
( 1973) has performed a series of experiments with 3 day old infants and concluded that reactivity is dependent upon the state of the subject, prandial condition, stimulus intensity, and the response parameter measured. The studies which support these conclusions will be briefly summarized below. 6 One factor affecting the type of response one may report is the
response measure employed. An example of a limiting measure is that
used by Bridger and Reiser (1959). They calculated the average heart
rate in the 5 second periods prior, during, and after stimulation, and
then computed any differences between the prestimulus and stimulus or
poststimulus period. Obviously, this response measure negates the
temporal characteristics of the response, and by using mean data, does not reflect the true maximal change as the result of stimulation.
Steinschneider (1971) has offered a more detailed analysis of the
response curve on each trial as an alternative to the above method.
This approach involves measuring such aspects of the response as pre
stimulus level, primary slope, peak magnitude, secondary slope, return magnitude, and prestimulus departure. Each stimulus response curve is
then reconstructed in graphic form from the extracted measures. This approach has been criticized by Graham and Jackson (1970) on the grounds that it is difficult to define the response measures in a way which allows for reliable extraction. Besides this inherent subjec tivity, there is the rigidity of the approach in that it applies only to the type of curve for which it was developed.
Steinschneider (1971) also employs an average response curve, constructed from the mean over all trials of the measures cited in the detailed analysis above. This approach is used for comparative pur poses; comparisons of response to different intensity stimuli, for different ages or groups of subjects, and for the study of different sense modalities. An alternative approach is found in Lipton, Steinschneider, and
Richmond (1961), and involves obtaining an average response curve by
computing the mean heart rate at small, fixed time intervals over all
trials. The obvious problems here are differences in both the tempo
ral component and magnitude of change over repeated trials. In all
cases, this approach will tend to underestimate the maximal change in
heart rate, and destroy the changes in temporal aspects of the re
sponse over trials.
A variable of major significance which affects both the magnitude
and direction of the cardiac response to any stimulus is the level of
functioning of the organism prior to stimulation. Wilder (1967) has
formulated what is known as the Law of Initial Value, which states that
the higher the prestimulus level, the smaller the response to function-
raising stimuli, and the larger the response to function-depressing
stimuli. The opposite holds for the lower prestimulus values. Com
parison of individuals on measures such as peak or trough magnitude
then, would have to correct for differences in the individual's pre
stimulus levels. It has been found, however, that the temporal as pects of the response are not affected by these prestimulus levels.
A correlate of the Law of Initial Value, there exists the phenom enon of the crossover point, explored by Bridger and Reiser (1959), which is the specific heart rate level at which there is no change with stimulation. Since the trend at higher levels is toward decel eration and at lower levels is acceleration, there theoretically exists a point at which neither of these responses occur. Interest in this phenomenon is due to the potential for reflecting individual differences in the level of the crossover point, as well as the fact
that the point defines for any subject the type of response expected
above and below that point. Moreover, Bridger and Reiser have dis
covered that this point is not affected by stimulus duration or age
of the subject, but is affected by stimulus intensity, with the
greater intensities raising the crossover point.
A second factor relating responsivity to the level of function
ing prior to stimulation has been elucidated by Porges, Arnold, and
Forbes (1973) and Porges, Stamps, and Walter (1974). By dividing
newborn subjects into two groups based on the measure of prestimulus
heart rate variability, they have shown that various response para
meters differ for the two groups, with high variability subjects
capable of response patterns resembling those of mature adults, but
low variability subjects capable of only attenuated acceleration.
Such research has led to increased interest in the measure of heart
rate variability, and the possibility that this measure may be an
index of neurological maturation.
Hutt, Bernuth, and Von Lenard (1968) have been concerned with
the role of state and its effects on the cardiac response over trials.
They have found that many of the response changes over time, as in
studies of habituation, have been due to changes in state and not in
the response itself. Hutt (1969) has said further that the probabil
ity and magnitude of a response are "almost without exception" a
function of state. Since reflexes other than the cardiac reaction
(e.g. spinal reflexes) are more readily elicited in one state than another, Hutt has said that states need not be placed on a continuum, 10 as from coma to alert wakefulness, but may be considered qualitative ly different neurophysiological conditions, each with a specific or ganization of its own.
Ashton (1971) studied the auditory responsivity of 3-5 day old babies in different states with four frequencies of stimulation. The newborns were found to be most responsive in the alert state, least responsive during either quiet sleep or crying, and differentially sensitive to different frequencies of auditory stimuli only during quiet sleep. The results were explained on the basis of the hypothe sis that during alertness and active sleep the central nervous system of the neonate is swamped by the intense stimulation, while during quiet sleep a low level of reactivity enables the neonate to respond differentially to different frequencies.
Sameroff, Cashmore, and Dykes (1973) presented alert infants with patterned visual stimulation and found that heart rate deceler ation occurred in response to a 12 X 12 checkerboard but not during a black-field control condition. They summarized that elicitation of orienting behavior during the newborn period seems to require an awake infant and a nonstartling, moderately complex stimulus.
Pomerleau-Malcuit and Clifton ( 1973) presented a stimulation in three different modalities to newborn subjects in different states.
They found that for sleeping subjects, the HR response was primarily accelerative to tactile and vestibular stimulation, but unreliable to auditory stimulation. For the awake subjects, the feeding variable affected the responsivity to auditory and vestibular stimuli, with the newborns responding more reliably and with less variability when tested before feeding. They summarized that the newborn's cardiac re sponse to stimuli in different modalities is affected by the state of arousal and feeding conditions.
Campos and Brackbill (1973) investigated the relationship between state, heart rate, and behavioral responding in 2 week old infants.
Their results indicated that state is a potent determinant of various behavioral and HR phenomena and was related to prestimulus HR levels.
They found that cardiac responses elicited in active sleep were larger than those elicited in a quiet awake state, even after prestimulus effects were partialled out. Further, the rate of response decrement over trials varied between infants remaining in the sleep state and those infants whose state changed during the series of stimulation.
Studying the relationship of cardiac responsivity and behavioral state is complicated by the above mentioned correlation between state and resting heart rate. Birns, Barton, Cronin, Newton, and Bridger
(1967) demonstrated in newborns the progression of increasing heart rate in association with increasing alertness of state from quiet sleep to crying. Lewis, Bartels, and Goldberg (1967) found essential ly the same thing for waking versus sleeping groups of infants. In terms of the relationship between state and resting heart rate then, evidence must be presented showing the influence of state on the cardiac response independent of prestimulus level if state itself is to be said to have an effect.
Steinschneider (1971) has addressed himself to this point, using statistical manipulations which correct for sleep versus awake differ ences on initial response and for prestimulus mean differences. The 12
results suggest that behavioral state is not a significant variable
in the newborn period. He summarizes that the developmental studies
have shown that state does appear to have an effect at later ages,
but in the newborn period state may affect the cardiac response only
through its effects on resting heart rate level.
The factor to be considered next as a determinant of the cardiac
response is the stimulus itself. Briefly, stimulus intensity, dura
tion, and modality are all variables affecting either the magnitude
or temporal aspects of the response. Steinschneider (1971) has stud
ied the cardiac response in a single newborn exposed to four intensi
ties of white noise: 55, 70, 85, and 100 dB. It was found that in
creasing the intensity of stimulation resulted in an increase in the
primary slope, peak, secondary slope, and return magnitudes. The
temporal aspects of the response were not affected.
Turkewitz, Birch, and Cooper (1972) presented 2 day old infants
a sequence of stimuli consisting of a white noise and a variety of
pure tones. The white noise was effective in producing cardiac ac
celeration whereas none of the pure tone stimuli produced an effect
that was different from the baseline level. The authors consider
their results to call into question those studies in which pure tones have been used as the stimuli in assessing cardiac responsivity and
its changes over repeated stimulation.
Stratton and Connelly (1973) studied the ability of 3 to 5 day
old neonates to discriminate between auditory stimuli along the dimen
sions of intensity, pitch, and time. Louder stimuli were found to
evoke larger initial cardiac responses and more rapid habituation. 13
The authors concluded that neonates can discriminate along each of
the auditory dimensions of intensity, pitch, and time based on dif
ferential responsivity within the habituation paradigm.
A study by Clifton, Graham, and Hatton (1968) focused on the var
iable of stimulus duration as the measure of interest. Groups of sub jects were presented with a 75 dB stimulus of 2-, 6 -, 10-, 18-, or 30- second duration. The cardiac response to all stimuli was an accelera tion, but peak magnitude, latency, and duration of response varied as the duration varied.
The variable of more of stimulation was focused on in a study by
Moreau, Birch, and Turkewitz (1970). Here the differences between auditory and tactile stimuli were looked at in terms of habituation.
Habituation, or loss of response to criterion, occurred significantly sooner to tactile than to auditory stimuli, with habituation to the auditory stimulus being gradual and systematic, whereas to tactile stimuli was abrupt and immediate.
Moreau et al. (1970) also studied habituation to repeated audi tory and somesthetic stimulation in two day old infants. Their re sults indicated that habituation of the muscloskeletal response was faster, more stable, and independent of habituation than the auto nomic response to the same auditory stimulus. The authors concluded that differences exist in the ease to which infants habituate to re peated stimulation in different modalities and the ease with which different responses habituate to the same stimulus.
Lipsitt and Jacklin (1971) have reviewed the prevalent findings that the human newborn cardiac response to exteroceptive stimulation is generally acceleratory, yet present a finding of cardiac decelera tion to an olfactory stimulus. Newborn infants were presented a series of odorant stimuli on two successive days while heart rate was continuously monitored. Cardiac deceleration was noted on a greater number of trials for the experimental vs. control group, was relatively consistent over both experimental sessions within each infant, and was considered a reliable individual difference measure.
The final factor to be mentioned here in its relationship to car diac responsivity is the age of the subject. Heart rate studies have been done with subjects ranging in age from prenatal to adult. Such studies have revealed a change from monophasic acceleration to di phasic acceleration-deceleration, and even triphasic deceleration- acceleration-deceleration, as the child develops. This age factor as a determinant of the response will be considered in more detail in the section on developmental studies of the cardiac response.
In summary, the cardiac response to stimulation is a delicate, variable response affected by many factors. Even when one controls for prestimulus level, state and age of the subjects, and intensity, mode, and duration of the stimuli, one must be sure to use a measuring device which is sensitive to the evoked response. Differences in how these factors are handled have made many of the studies in this area either difficult to replicate or incomparable with one another.
THEORIES OF THE CARDIAC RESPONSE TO STIMULATION
A major portion of the early work in psychophysiological respon sivity attempted to fit its data into a theory of activation or arousal
(Malmo and Belanger, 1967). It had been considered that behavior could be scaled along a continuum of intensity ranging from low levels dur ing coma or deep sleep to a high level during alert wakefulness and strong emotion. While some evidence has shown a relationship between • activation and behavioral efficiency, this theory has been attacked for its unidimensionality aspect. Lacey (1967) has reviewed the evi dence which casts doubts on the theory. Included in this evidence are the lack of significant intercorrelations among various autonomic measures of arousal, the dissociation of central, behavioral, and autonomic measures, and the specificity of autonomic arousal responses as a function of stimulus situations. Proponents of unidimensional arousal theory argue for the theory's value in general description and have stated that problems exist due to the lack of separation between long term changes and discrete responses. Nevertheless, arousal theory is not applied today in the explanation of cardiac response data.
An alternative approach is offered by Routtenberg (1968), who feels a maximal amount of the variance in cardiac response measures can be accounted for by postulating two arousal systems rather than one.
It is said that neurophysiological data can be accommodated by consid ering two mutually inhibiting arousal systems, each with its own specific function. The first of these is evoked by high intensity stimulation and is associated with the Moruzzi and Magoun (1949) re ticular activating system, which acts to limit the effect of the stim ulation. The second is evoked by low and moderate intensity stimuli, and involves the limbic ststem, which acts to prolong the effects of stimulation and facilitate memory and learning processes. A theory similar to that of Routtenberg's is the conceptualiza
tion of Sokolov (1963), who postulates two generalized reflex systems,
the orienting reflex and the defensive reflex. The defensive reflex
is evoked by high intensity stimuli and functions to limit stimulus
effects. The orienting reflex is evoked by novel or signal stimuli
that are below the levels which would evoke the defensive reflex, and
functions to enhance stimulus effects and strengthen associations.
With repeated presentation of the novel stimulus, the orienting reflex
diminishes, a factor suggested as evidence for habituation and early
learning in newborn studies. Lynn (1966) has attempted to relate
Sokolov's reflexes to specific brain areas and cites evidence to link
the orienting reflex with the limbic system and the defensive reflex with the brain-stem reticular formation. Sokolov suggests that the
cortex serves to analyze incoming stimuli and signal the orienting or defensive reflex to amplify or dampen response effects.
The current prevalent theory is that of John Lacey (1959), who
cites neurophysiological and behavioral data to support the idea that heart rate deceleration occurs during "intake" of stimuli, and heart rate acceleration occurs in situations of stimulus "rejection." De celeration is supposedly the organism's way of increasing receptivity to external events. Lacey sees the response serving an "instrumental"
function, based on the fact that a change in the rate of sensory af-
ferents from the heart stimulates the carotid sinus to discharge.
These signals are passed to the reticular formation, and from there to the cortex. This cortical bombardment decreases sensitivity to inputs from various senses. A slow steady heart rate minimizes these noisy signals from the carotid sinus and results in heightened sensitivity.
Graham and Clifton (1966) have extended this idea and suggested that deceleration should be a component of the orienting reflex and accel eration a component of the defensive reflex. A review of the evidence by Graham and Clifton (1966) has supported this idea.
Obrist (1969) offers an alternative approach, and states that a decrease in heart rate is the result of vagal excitation, and is ac companied by a corresponding decrease in motor activity. Heart rate is said to decrease as the organism becomes quiet, and cardiac and somatic decreases are seen as different biological manifestations of the same process. Obrist cites neurological data to support the idea that the cingulate gyrus and related subcortical pathways appear to be involved in both somatic and cardio-vascular inhibitory effects.
Kagan (1971) supports this approach, citing several studies where de celerations are accompanied by decreased motor activity.
A critical consideration of both the Lacey and Obrist theories is found in Hahn's (1973) comprehensive review. After detailing the lon gitudinal development of the Lacey theory, its supportive evidence and alternative views, Hahn concludes that the theory may retain its heu- istic value if a clarification of constructs such as "attention" is forthcoming, if alternative dependent measures beyond heart rate are offered to reflect mediating mechanisms and control effects, and if alternative hypothesized mediating mechanisms are investigated.
Brackbill (1971) reports an investigation of an anencephalic and normal infants in an attempt to assess the role of the cerebral cortex in the expression and inhibition of the orienting reflex. She 18
concludes that while the anencephalic infant was as effectively re
sponsive to environmental stimulation as the normal infants, the a-
bility to cease responding to repeated stimulation was impaired, as
was the ability to modify the amplitude of its response. The role
of higher brain structures in the habituation process is suggested.
Greaves and Lynch (1972) review the various theories which pro
pose a specific role of the brain stem reticular formation in re
sponse decrement, and summarize that the involvement of this brain
area has been a persistent theme and is well established. They
further cite anatomical and experimental evidence to support a model of how the reticular formation may be involved on the cellular level
in response habituation.
Greenberg, O'Donnell, and Crawford (1973) studied 11 week old
infants in an attempt to relate rate of habituation with level of complexity of stimulation. The hypothesis considered was that in fants able to process information most rapidly would be more advanced in cognitive-perceptual development than those infants who were not as rapid processors of information. The hypothesis was supported by the data, and the authors concluded that attentional variables may be important indices of intellectual-developmental behavior in infancy.
DEVELOPMENT OF RESTING HEART RATE AND ITS VARIABILITY
Michael Lewis (1970) has measured resting heart rate in subjects from the last trimester before birth to one year of age. Fetal heart rate was found to be fairly stable, while an elevated heart rate after birth was evident which did not return to fetal level until around 9 months after birth. The major finding is that of a linear decrease of 19
heart rate with age through the first year of life.
Steinschneider (1971) has reported an increase in heart rate
from birth to three months of age, after which time the heart rate de
creased through childhood to the adult level around 16 years of age.
Frances Graham (1968) has studied neonatal resting heart rate
and found that over the first five days of life there is an increase
in rate.
Parmelee, Wenner, Akiyama, and Flescher (1964) did a longitudin
al study of normal and premature infants' resting heart rates, find
ing a decrease over time in normal infants' heart rates, but a tend
ency for the premature infants' heart rates to remain fairly high.
Hon (1968) has studied fetal and neonatal heart rate patterns,
and has found a correlation between fetal heart rate patterns the
last half hour before delivery and the neonatal heart rate patterns.
If deceleration of normal fetal level is present just before deliv
ery, there is usually a neonatal tachycardia which persists for 20-30 minutes after birth. Many other effects of the birth process on
fetal and then neonatal heart rate are enumerated by Hon.
In summary, there is a general agreement on the decrease of the
resting heart rate over time from 3 months of age to adulthood. How
ever, the prenatal to 3 months postnatal period is evidenced by some confusion, and a lack of normative, descriptive studies in this area
is evident.
The results of comprehensive work in fetal heart rate monitoring have been published in an atlas by Edward Hon (1968). Hon has ad dressed himself to the methodological problem evident in the field, and detailed the newer instrumentational methods which have allowed
for a more precise analysis of fetal heart rate patterns than the old methods of auscultation. The atlas contains hundreds of records de scribing the reaction of the fetal heart rate during the birth process, its reaction to maternal contractions and other natural as well as un natural factors in the course of birth and development. With the new methods Hon has discovered the fetal heart rate deceleration during maternal contractions mentioned earlier in this review, citing pres sure on the fetal head as the causative factor. With such monitoring
Hon has discovered what are ominous signs in fetal condition, and when it is advisable to discontinue labor and deliver the fetus.
With the modern electrical techniques Hon was able to visibly see variability around the baseline of the heart rate printouts, what he calls irregularity. In addressing himself to the meaning of variabil ity of irregularity in infant or fetal condition, Hon has said that irregularity, rather than being an ominous sign, is a positive indi cator that the fetus has a functioning well-developed nervous mechan ism for controlling its heart rate. He states further that one aspect of fetal heart rate which has not received adequate attention is the absence of irregularity, a baseline which is fixed or smooth. It is said this type of fetal heart rate baseline indicates that the nervous control mechanisms of the fetal heart are not fully developed or have been blunted by drugs or fetal deterioration. Based on tachograph records, Hon has classified irregularity on a continuum from no irreg ularity to marked irregularity, and constructed measuring devices one could place over a record in order to classify irregularity into one of the five categories. Figures in Hon's atlas show the tachograph records of infants
with various involvements before and during birth, with description
of the later development of the child. The records showing flat or
smooth baselines with no variability were: a premature infant at 32
weeks gestational age, the fetus of a 41 weeks of gestation toxemic
mother, the fetus of a woman with maternal fever, the fetus of a
woman having received barbiturates, the fetus of a mother given a
tranquilizer (the type and route of administration determine dura
tion of the effect on fetal heart rate), and finally the fetus of a
mother after administration of atropine. Oddly enough, Hon notes the
records of several individuals whose irregularity actually increases
as labor progresses, explained as the "tuning-up" effect that labor
and the birth process have on the autonomic nervous system.
To summarize, the normal heart rate pattern of a fetus or new born contains irregularity or variability around the baseline, in
dicating constant increases and decreases in rate occurring in healthy balance. When these changes are absent, and the baseline
is smooth, it is an ominous, unhealthy sign.
Vallbona, Rudolph, and Desmond (1965) were concerned with changes
in irregularity or variability with age in groups of premature infants of varying birth weights. They state that the absence of fluctuations
in baseline heart rate suggest an immaturity of the centers of cardio- regulation or a functional interruption of the pathways transmitting regulatory impulses. In the course of this study, it was found that common maternal medications did not affect fluctuations of heart rate in the newborn, and that differences in regularity were a function 22
of neonatal condition and not maternal effects. The authors conclud ed that in premature infants there is the presence of cardioregula-
tional activity, but due to the immaturity of the centers, this ac
tivity was not as marked or active as in the full term neonate.
In a study of heart rate patterns in newborn infants which at
tempts to find screening and diagnostic value in such data, Urbach
(1965) has addressed himself to the question of regularity and vari ability of the heart rate pattern. Of the group of 21 infants with flat heart rate patterns studied, 13 were reported to have died, 4 were seriously ill, and 4 were not obviously ill, but questionable as to future development. Urbach states that infants with flat heart rate patterns who survived all recovered normal variation or irregu larity before recovery. He further comments that normal rate changes to various stimulation and normal body function did not occur in the flat record group and concludes that the lack of response shows a diminished sensitivity to these inputs, a conclusion important in terms of the present study.
In a series of studies on fetal heart rate patterns, deHaan
(1971) has produced an even finer analysis than that of Hon (1968).
In the first of these he described two types of irregularity: rapid fluctuations or short term irregularity with an amplitude of 1 to 8 beats per minute, and slow fluctuations or long term irregularity whose frequency may be one cycle every 4 or 5 minutes. In the second of these studies he summarized the conditions associated with the disappearance of both of these types of irregularity resulting in a flat pattern. These are: maternal fever, fetal distress, immature 23 fetuses, congenital malformations such as anencephaly and heart block, and maternal drug administration of autonomic or sedative type.
DEVELOPMENTAL STUDIES OF THE CARDIAC RESPONSE TO STIMULATION
Studies of the fetal cardiac response to stimulation date back to the work of Sontag in the early 1940's. Typical of this early study was a report (Sontag, 1941) that described a variable fetal heart rate as a result of external vibration of the maternal abdomen. Larks
(1964) has employed the modern techniques of fetal heart rate monitor ing and demonstrated that fetal electrocardiograms may often show characteristics similar to those of newborn infants, and are even mod ified by maternal disease.
Sontag has more recently (1969) studied the concurrent fetal and maternal cardiac response to environmental stimulation. Results indi cated that the mother's heart rate change predicted the nature and direction of the fetal response. The methodological problem inherent in the results was that it was uncertain whether the mother served as a mediator of the fetal response, through increased background noise or an endocrine mechanism, or if the fetus was responding independent ly. The study by Grimwade (1971) was directed at this issue. By presenting a stimulus which the mother was unable to hear, and to which there was no change in the maternal heart rate, Grimwade was able to conclude that the resultant fetal acceleration was a direct response, independent of the mother, to the stimulus.
Graham and Jackson (1970) have reviewed the early work in newborn cardiac responsivity and stated that in the vast majority of cases 24 discrete stimuli evoke heart rate acceleration. Exceptions to this trend, however, have been noted, such as results reported by Vallbona,
Desmond, and Rudolph (1963). They investigated cardiac activity in the first hours of life and demonstrated that the heart rate response to an external stimulus may be an acceleration followed by rebound deceleration. Graham and Jackson (1970) note that at the time the early neonate studies were published, it was not yet known that a de celeration of the heart rate characterized a mature, adult orienting response. The best evidence at the time showed the typical response of the adult was brief acceleration followed by larger deceleration.
Yet it was not then evident that the response showed a change with age, since methodological weaknesses in response measures character ized the newborn studies. It was considered that more detailed anal ysis might reveal a secondary deceleration in the newborn.
The need for more detailed analysis was met by several research ers, among them Keen, Chase, and Graham (1965). Their study, along with several others, looked at the response for over 20 seconds after stimulus onset, and still found only a monophasic acceleration with no significant deceleration below prestimulus levels.
Studies by Graham (1968) replicated the findings showing no secondary deceleration, but raised the question of whether longer response measures and longer duration stimuli might be more effec tive in eliciting deceleratory responses in newborns.
The question of longer duration stimuli affecting deceleration was considered by Clifton, Graham, and Hatton (1968). In response to a 150 second presentation of an auditory stimulus, there was an 25
initial accelerative wave which was not followed by any significant
deceleration below prestimulus level.
Jackson, Kantowitz, and Graham (1971) have considered the ques
tion of whether newborns are capable of exhibiting cardiac orienting.
Their concern was the removal of the objection that newborns were gen
erally studied in drowsy states with stimuli that might evoke startle
responses, and therefore might be prevented by procedural matters
from eliciting the mature HR deceleration typical of older infants
and adults. Despite these methodological safeguards, the authors were
forced to conclude from the data that no convincing evidence of de
celeration existed. Their results continued to suggest that it is
difficult to elicit the cardiac component of orienting from newborns
even under optimal conditions.
Conflicting data, nevertheless, are beginning to appear in the
literature. Adkinson and Berg (1976) offer evidence that newborns are
capable of cardiac deceleration. Selecting a group of newborns based
on altertness, and presenting mild intensity colored light stimuli,
they found these 4 day old infants capable of heart rate decelerations
to both stimulus onset and offset. The authors conclude that under
optimal conditions, cardiac deceleration is possible, but whether or not this deceleration is reflecting a mature orienting reflex is
questionable. Similar results are reported by Clarkson and Berg
(1978), who suggest that newborns are capable of cardiac orienting, and that the probability of eliciting an orienting reflex is offset by several stimulus parameters and subject characteristics. 26
Stamps (1980) considered the onset and offset heart rate responses
to auditory stimulation in full term healthy newborns. By splitting
the infants into high and low birth weight groups, he found that only
the high birth weight group responded to both stimulus onset and off
set. Infants falling below the median birth weight showed no response
to either onset or offset. The author concluded that maturation was
the key factor in determining the ability to respond in this paradigm,
and that the heavier group exhibited this higher level of maturation.
Cardiac response studies with older infants have established the
fact that at some point in the first few months of life heart rate de- cleration is elicited as the primary component of the orienting re
sponse, replacing the immature accelerative pattern of the newborn.
Brown, Leavitt, and Graham (1977) have studied the response of 6 and
9 week infants to auditory stimuli. Even under optimal conditions
for eliciting orienting, no significant cardiac response appeared at
6 weeks, while a significantly decelerative response was evident at 9 weeks. The authors concluded that a developmental change in orienting may occur in young infants and that the probability of eliciting the response varies with stimulus characteristics.
Rewey (1973) investigated the effects of state and age on the cardiac component of both the orienting and defensive reflex in 6 and
12 week old infants. Age related changes in the response were more closely evident when state was held constant, and supported the notion of greater monophasic decelerations for the 12 week old group.
Berg (1974) has studied the cardiac component of the orienting response in 6 and 16 week old infants. His findings suggest that when 27
state is tightly controlled within a narrow alert range, the 6 and 16 week old infants were both capable of a mature cardiac deceleration on the initial trials of the stimulus sequence. When conditions how ever, are less well-controlled, the suggestion is that the younger infants fail to show the mature response while the older 16 week group continues to perform as in the alert state.
Berg (1972) has also considered the factors of habituation and dishabituation of the cardiac response in a group of 4 month old, a- lert infants. His concern in the study was whether the characteris tics of rapid habituation, dishabituation with stimulus change, and elicitation by stimulus offset would be demonstrable in a 4 month old sample known to be capable of mature cardiac deceleration. The re sults supported the hypothesis that all of the above characteristics of mature cardiac orienting are demonstrable by 4 months of age.
Similar results are reported by Chang and Trehub (1977) for 5 month old infants.
Gray and Crowell (1968) used 3 types of stimuli and subjects of varying ages and found in all cases a deceleration increasing with age which, by 11 weeks, took over as the primary response, followed by some secondary acceleration. Lipton, Steinschneider, and Richmond
(1966) have shown in 5 month old infants a triphasic response of brief deceleration, acceleration, and subsequent decrease below pre stimulus level, as a result of tactual-pressure stimuli.
Cardiac response studies with older infants have repeatedly shown deceleratory phases similar to those of the adult. In 6 month old in fants Meyers and Cantor (1967) found a slight acceleration followed by 28 a greater, more significant deceleration in response to a visual stim ulus. Further studies have shown even greater decelerations in re sponse to visual and auditory stimuli, as well as speech sounds.
Sostek and Brackbill (1976) studied the stability of the orient ing reflex rate of habituation as a trait reflecting consistent indi vidual differences. They found that the habituation rate of a motor orienting reflex did not differ significantly over three sessions dur ing the first month of life. Further, the habituation of the heart rate orienting reflex was relatively stable fom 4 to 8 months of life in a test-retest paradigm. The authors conclude that the rate of ha bituation is an individual difference trait with relative stability and predictive of future stimulus processing behavior.
Finally, Kagan (1971) has studied cardiac responsivity in a cross- section of 4, 8, 13, and 27 month old infants in an attempt to deter mine the developmental changes in the response and the stability of various individual differences. His results indicate a steady decrease in the magnitude of deceleration with age and greater stability in the characteristics of the response over time for boys than girls.
The above noted results clearly support the view that a shift in the heart rate response from the newborn acceleratory pattern to the more mature deceleration typical of children and adults occurs some time in the first months of life. It is not known exactly why this shift occurs, though several hypotheses are presented. Among these are maturation of higher nervous system centers, characteristics of the stimuli employed in the studies, the state of the subjects in the various studies, and the postnatal experience of the subjects. 29
SUCKING BEHAVIOR IN THE HUMAN INFANT
Studies of human infant sucking behavior have been concerned with differentiating the nutritive and non-nutritive modes, determining the influence of factors such as state, sedation, and subject characteris tics 011 the behavior, and considering the use of the sucking response as a dependent variable affected by environmental stimulation, rein forcement, and learning.
Sameroff (1965) has described the apparatus which in some form is used in a majority of explorations into mammalian sucking behavior. A combination of pacifiers, pressure transducers, a polygraph, liquid pumps and tubing allow for the measurement of sucking pressure, expres sion pressure, amount of nutrient consumed, sucking rate, and the timed delivery of stimulation and reinforcement. Employing such an apparatus has allowed for the differentiation between nutritive and non-nutritive modes of sucking in the human newborn. The nutritive mode (Wolff,
1968) has been shown to prevail as long as some palatable liquid is available through the nipple, while the non-nutritive style is evident when an infant sucks on a blind pacifier. The nutritive mode of suck ing occurs in a continuous stream of sucks with equal time periods be tween successive sucks. The non-nutritive mode, however, is charac terized by an alternation of bursts of sucking and rest periods, the pattern of which are fairly stable for any one infant. The non nutritive mode is also seen to occur spontaneously in drowsy or sleep ing infants. Shirataki (1973) has confirmed that the nutritive and non-nutritive modes have a different developmental character, with nutritive sucking movements well-developed at birth and capable of 30 adapting to a change in surrounding conditions, while non-nutritive movements develop rapidly the first week of life and diminish at three months of age. Shirataki considers non-nutritive sucking move ments to play an active role in the transition from the state of alert wakefulness to the states of restfulness and sleep.
The effects of state on sucking behavior have been considered by several researchers. Dreier and Wolff (1972) considered the rhythmic features of non-nutritive sucking behavior in normal and high risk in fants and compared the characteristics of the response in two distinct sleep states. They concluded that in normal infants the patterns of non-nutritive sucking behavior differed significantly between states
(regular vs. irregular sleep), while for the high risk group no state effect was noted. Goldie, Rhodes, and Roberton (1970) considered sucking behaviors in the states of eye-movement vs. non-eye-movement sleep and related the sucking movements to EEG changes. Their re sults indicated that sucking movements occurred only in the non-eye- movement phase of sleep and were generally noted just prior to bursts of high amplitude EEG activity. Bell and Haaf (1971), however, re ported somewhat conflicting data. They investigated non-nutritive suck ing behavior across six different states, ranging from low wakefulness to agitated crying. Their results suggested that for this wide range of states, there was no significant relationship between measures of sucking behavior and state. In summary, the effects of different states on aspects of non-nutritive sucking behavior remains unclear.
The EEG changes noted by Goldie et al. (1970) following bursts of non-nutritive sucking are supported by data relating heart rate to 31
sucking behavior. Gottlieb and Simner (1966) studied sucking behavior
while continuously monitoring the newborn's heart rate. Their results
indicated that significantly high levels of heart rate were associated
with spontaneous bursts of non-nutritive sucking. Further, non-nutri
tive sucking was anticipated by and predictable from a rise in heart
rate. Soentgen, Pierce and Brenman (1969) studied the nutritive mode
of sucking and found the same significantly high heart rate during bursts of sucking activity. They concluded from their data and from
summaries of the neurological activities required in the sucking act,
that the measurement of neural interrelationships reflected in the
sucking act may be helpful in evaluating the neurological state of
the newborn, and identifying high risk infants without gross evidence of neurological involvement, a view supported by Wolff (1972).
The effect of obstetric sedation on newborn sucking behavior has been considered by Kron et al. (1966). They studied nutritive suck
ing through the first 4 days of life in two groups of infants, a con trol group and a group whose mothers received obstetric sedation by
intravenous injection. The results indicated that the control group had higher average sucking rates, pressures, and volumes of consump tion than the "experimental" group of the same chronological age.
Day by day increases in each measure were noted in the "experimental" group which was attributed to a recovery effect from the drug.
Subject variables have been a major interest for investigators in the field of neonatal sucking behavior. Kron et al. (1968) stud ied nutritive sucking behavior over the first four days of life in a group of healthy full term infants. They found consistent individual 32
differences between infants on the repeated measures of nutritive suck
ing behavior, with sucking pressure the most discriminating response.
The authors conclude that sucking behavior allows for the measurement
and elicitation of consistent individual differences that may be pre
dictive of the course and nature of future psychological development.
The effects of prematurity on sucking behavior have been consid
ered by Dubignon et al. (1969). They investigated non-nutritive suck
ing patterns in a group of premature infants in order to assess at what point the full term sucking pattern emerges and to determine the
effects of maturity and postnatal experience on the sucking patterns.
Their results indicated that sucking times and counts remained below
full term levels until the 37th postconception week while sucking rate
reached the full term level at about the 34th postconception week. In general, less mature infants spent less time sucking and had lower
sucking counts than the more mature infants. With feeding experience equated, the more mature infants showed higher sucking scores. The authors conclude that non-nutritive sucking patterns in premature in fants are primarily a function of maturation, and are best regarded as a reflection of a simple reflex motor behavior which is relatively in dependent of postnatal age or feeding experience.
Gryboski ( 1969) has studied the nutritive patterns of suck and swallow in premature infants. These results suggest a development of nutritive sucking behavior from an "immature suck-swallow pattern," which is characterized by short bursts of sucking at a rate of 1 to
1.5 sucks per minute preceded or followed by swallowing, to a mature pattern with bursts of 30 or more sucks at a rate of 2 per second, 33
with swallows occurring routinely during the sucking burst. The auth
or postulates a protective function of the immature pattern that pre
vents the delivery of a large amount of nutrient which the esophagus
is developmentally unprepared to handle.
The extension of the methodology to the sample of high risk in
fants is typified by Kron, Litt, and Finnegan (1973), who considered
the behavior of infants born to narcotic-addicted mothers. They
studied 43 infants born to heroin or methadone addicted mothers, em ploying the usual nutritive sucking measures of rate, pressure, a- mount of nutrient consumed, etc. Their results indicated significant
reduction in sucking rates and pressure for both heroin and methadone
addicted groups relative to the control group. Further, significant differences were also found between the heroin and methadone group, with infants of methadone addicted mothers more depressed in their
sucking behavior. The authors concluded that the decrease in sucking activity is consistent with the general CNS depressant action of these drugs which readily cross the placental barrier.
A few studies (Wolff, 1968; Dreier and Wolff, 1972) have employed non-nutritive techniques to assess the sucking rhythms of infants with a history of perinatal distress in comparison to infants having a be nign perinatal history. These results indicate depressed sucking rates for infants with chromosomal defects, decreased sucking rates, and greater intraindividual variability for infants with a history of hy poxia, decreased sucking rate, greater interburst variance of mean rate and greater incidence of rapid tremors of the sucking curve for infants with hyperbilirubinemia, and similar decreased rates and 34
increased variance for infants with dysmaturity and suffering neonatal
seizures. The authors conclude that infants with presumptive evidence
of CNS involvement differ from normal infants with respect to the tem
poral organization of rhythmical motor behavior even when overt signs
of neurological impairment are absent.
A major value of human infant sucking behavior lies in its use as
a dependent variable in studies concerned with different modalities of
stimulation and their effects on infant behavior. Kaye (1966) inves
tigated the potentiality of using nutritive sucking response measures
as dependent variables in the study of tone intensity discrimination
and the effects of feeding. The results indicated that the ingestion
of liquid suppressed sucking measures, with the amount of suppression
a function of the amount of liquid consumed. Further, the rate of
sucking increased significantly during the presentation of loud tone
stimulation, this effect partially counteracting the suppressive ef
fects of liquid ingestion. Miller (1975) investigated changes in non nutritive sucking patterns contingent upon the presentation of an au ditory stimulus in a sample of premature infants. No significant changes in the rate of sucking were noted as a function of auditory stimulus presentation. The authors conclude that since marked heart rate accelerations were noted in the premature sample to the same stimulus, the lack of alteration of sucking patterns suggests that for the premature group the sucking response is not an especially sen sitive index of responsiveness to external stimulation.
For the newborn infants, Sameroff (1967) has demonstrated that an inverted U-shaped relation exists between level of light intensity and 35
the number of sucking bursts. Further, a sound stimulus was shown to decrease burst frequency of non-nutritive sucking. Simner (1969) ex posed newborn infants to one of four rates of photostimulation while
they were engaged in non-nutritive sucking. The results indicated
that a maximum increase in sucking was displayed by the group exposed
to a flash stimulation rate falling within the range of the fetal heart rate during midgestation. The authors cite these results as support for the cardiac self-stimulation hypothesis which suggests that exteroceptive stimulation available to the fetus from its own heart beat in utero may promote the establishment of prenatal as sociations that affect the newborn's display of reflex patterns.
Barrett and Miller (1973) investigated the effects of unpatterned and patterned light stimulation on non-nutritive sucking behavior in premature infants. The results indicated both stimulus contingent sucking acceleration and suppression varying with the type of stimula tion, with evidence for shorter duration rate changes in the younger, less mature group. Haith, Kessen, and Collins (1969) studied the ef fect of three levels of complexity of a visual stimulus on non-nutri tive sucking behavior in 2 to 4 month old infants. The results indi cated suppression of sucking behavior under all levels of stimula tion, with the largest suppression of sucking on the first experimen tal trial of each session. Kessen (1967) considered sucking and looking behavior in the human newborn and summarized a series of ex periments. Sucking was shown to have a significant effect on the re duction of movement, with higher rates of sucking effecting decreases in motor movement. Further, infants could be divided into "good" and 36
"poor" suckers, with the implication that "good" suckers were more mature and further developed than the "poor" suckers. The conclusion was made that a congenital relationship exists between sucking and movement, that there is a congenital relationship between feeding and activity, and that a developmental change in the first days of life occurs which increases the likelihood of sudden quieting when sucking.
The effects of reinforcement and learning upon aspects of human sucking behavior have been considered in several studies. Lipsitt and Kaye (1965) have demonstrated differential sucking rates to rub- ber-tube and rubber-nipple stimuli to support the notion that the readiness and vigor of sucking responses are in part determined by the size and shape of the intraoral stimulus. Further, experience with the nipple stimulus increased the frequency of response to the tube stimulus, demonstrating conditioned enhancement. Lipsitt, Kaye, and Bosack (1966) found that reinforcement with a dextrose solution enhanced the rate of sucking on a tube-type stimulus in the human newborn, and concluded that the effects were attributable to condi tioning. In an extension of this study, Lipsitt, Reilly, Butcher, and Greenwood (1976) measured the sucking behavior of newborns while continuously monitoring heart rate and respiration. Their results indicated that measures of sucking were affected by the presence or absence of sucrose reinforcement. Also noted were increased heart rates when sucking for sucrose despite the fact that sucking rate decreased under the reinforcement condition. Other studies (Crook,
1976; Burke, 1977) report results which support the notion of de creased sucking rates and increased heart rates under the reinforce ment condition. 37
Hillman and Bruner (1972) manipulated schedules of milk rein forcement to determine the effects on infant sucking behavior. They found that infants were capable of responding differentially to the varying schedules of reinforcement, with 3-4 month old infants more sensitive to changes in the schedule than 1-2 month old newborns.
Kron (1968) summarized a series of experiments concerned with the effects of arousal and learning upon patterns of nutritive suck ing behavior. The results showed that infants were capable of rapid adaptation to varying schedules of reinforcement. Kron concluded that infant behavioral acquisition begins with unconditioned feeding responses which are molded into complex learned behaviors through the effects of a differentially reinforcing environment. CHAPTER III
METHODOLOGY
This chapter is divided into three sections, covering in succes
sion the characteristics of the subjects, the specific experimental procedures employed, and the methodological issues considered.
SUBJECT CHARACTERISTICS
Twenty healthy full term, twenty premature, and twenty high risk
full term infants were employed as subjects in this study. The healthy
full term infants (10 males and 10 females) were randomly chosen from
The Ohio State University Hospital's Newborn Nurseries, and all met the
following criteria:
1. Vaginal birth with normal pregnancy and delivery.
2. Apgar s c o r e ^ 8 at one and five minutes and normal cord
blood biochemistries.
3. Normal clinical examinations during the hospital stay.
It is noted here that the Apgar score is a measure of infant con dition, estimated by the attending physician at one and five minutes after birth, which consists of a ranking 0, 1, or 2 on five varia bles: heart rate, respiratory effort, reflex irritability, muscle tone, and color. In this schema, scores range from 0 for a stillborn child
38 39
to 10 for a vigorous, healthy newborn. Descriptive characteristics
for the healthy full term infants are listed in Table 1. The race
factor was not considered relevant to the purposes of the study, and
is not reported.
The premature infants (10 males and 10 females) were chosen as
they became available, usually from The Ohio State University Hospi
tal’s Neonatal Intensive Care Unit, where they were receiving regular
care. They met the following criteria:
1. Low birth weight (<1750 gms.)
2. Gestational age of 36 weeks or less as estimated from
maternal history and clinical evaluation of the newborn.
Due to continued medical treatments, special care, and overall frail
ty, it was deemed best not to test the premature infants at an extra-
uterine age comparable to that of the full term infants. Rather they
were tested at the time they were considered to be in a healthy con
dition, whether they had been moved to open bassinets or were still
in isolettes. This was generally one to two weeks after birth, making
the gestational age at testing 34.6 weeks for the males and 34.9 weeks
for the females. Characteristics of the premature infants are listed
in Table 2.
The high risk full term infants (10 males and 10 females) were chosen as they became identified from either the Newborn Nurseries or
the Neonatal Intensive Care Unit of The Ohio State University Hospital.
All met at least one of the following criteria:
1. Infants depressed at birth (Apgar score ^ 6 at one and
five minutes). 40
2. Offspring of diabetic mothers.
3. Infants with blood group incompatibilities.
These infants were tested at an age comparable to that of the healthy full term group, usually the third or. fourth day of life. Character istics of the high risk full term group are listed in Table 3.
Parental permission was obtained in all cases, consisting of the mother's or father's signature on a written consent form (See Fig ure 1). The mother was informed in all cases of the procedures to be performed, possible risks involved (there were none), and the pur poses of the study. Parents were invited to witness the entire pro cedure if they so desired.
EXPERIMENTAL PROCEDURES
Once an infant was determined to have satisfied the criteria for one of the subject categories, and the parental consent was obtained, the infant was taken at the appropriate time from the nursery, wrap ped in a blanket and moved to the testing room. This room was kept at a constant temperature of 76 degrees F. with a humidity index a- round 42%. The ambient noise level when all equipment was operating was approximately 78 dB SPL; over half of this noise was from low fre quency tones of less than 100 cps. The infant was placed in an open bassinet and three Grass EKG electrodes were applied; one to the mid dle of the back, one to the base of the sternum, and the ground elec trode on the abdomen. The electrodes were gold-plated surface elec trodes held in place by surgical paper tape, with electrode cream added to the surfaces to insure optimal conductivity. The infant was then rewrapped in its blanket and left to rest. In the case of the 41
TABLE 1
SUBJECT CHARACTERISTICS HEALTHY FULL TERM INFANTS
MALES (N=10) MEAN STD.DEV. MAX. MIN. RANGE
BIRTH WT. (gms.) 3381.6 430.7 4300 2865 1435 LENGTH (Cms.) 51.0 2.4 56.0 47.5 8.5 HEAD CIRC. (Cms.) 34.7 1.2 36.0 32.5 3.5 APGAR (1 Min.) 8.7 . 15 9 8 1 APGAR (5 Min.) 9.0 . 17 10 8 2 TEST AGE (Hrs.) 63.0 11.3 78 46 32
FEMALES (N=10) MEAN STD.DEV. MAX. MIN. RANGE
BIRTH WT. (Gms.) 3418.0 361.9 4100 2915 1185 LENGTH (Cms.) 51.0 1.7 53.5 48.5 5.0 HEAD CIRC. (Cms.) 34.5 1.9 38.5 32.5 6.0 APGAR (1 Min.) 9.1 . 14 10 8 2 APGAR (5 Min.) 9.1 .16 10 8 2 TEST AGE (Hrs.) 57.9 10.5 78 43 35 42
TABLE 2
SUBJECT CHARACTERISTICS PREMATURE INFANTS
MALES (N=10) MEAN STD.DEV. MAX. MIN. RANGE
BIRTH WT. (Gms.) 1564.9 165.8 1750 1300 450 GESTATIONAL AGE AT BIRTH (Wks.) 33.1 1.6 36.0 31.0 5.0 TEST WT. (Gms.) 1786.0 274.4 2270 1260 1010 GESTATIONAL AGE AT TEST (Wks.) 34.6 1.7 37.0 31.0 6.0 LENGTH (Cms.) 41.6 1.5 43.5 39.0 4.5 HEAD CIRC. (Cms.) 30.0 2.0 33.0 27.0 6.0 APGAR (1 Min.) 6.9 1.1 9 4 5 APGAR (5 Min.) 7.8 .9 9 5 4
FEMALES (N=10) MEAN STD.DEV. MAX. MIN. RANGE
BIRTH WT. (Gms.) 1546.8 396.2 2095 920 1175 GESTATIONAL AGE AT BIRTH (Wks.) 32.7 3.3 37.0 26.0 11.0 TEST WT. (Gms.) 1772.3 262.9 2185 1320 865 GESTATIONAL AGE AT TEST (Wks.) 34.9 1.1 37.0 33.5 3.5 LENGTH (Cms.) 42.1 3.6 46.0 35.0 11.0 HEAD CIRC. (Cms.) 28.9 2.5 31.5 24.0 7.5 APGAR (1 Min.) 7.0 1.2 9 3 6 APGAR (5 Min.) 8.3 .7 9 7 2 43
TABLE 3
SUBJECT CHARACTERISTICS HIGH RISK FULL TERM INFANTS
MALES (N= 10) MEAN STD.DEV. MAX. MIN. RANGE
BIRTH Wt. (Gms.) 3304.5 523.3 4200 2330 1870 LENGTH (Cms.) 52.0 2.5 55.5 46.5 9.0 HEAD CIRC. (Cms.) 34.9 1.0 36.0 33.0 3.0 APGAR (1 Min.) 3.7 2.2 6 0 6 APGAR (5 Min.) 4.9 1.1 6 1 5 TEST AGE (Hrs.) 76.7 26.5 120 47 73
FEMALES (N=10) MEAN STD.DEV. MAX. MIN. RANGE
BIRTH WT. (Gms.) 3552.3 609.0 4540 2720 1820 LENGTH (Cms.) 51.1 2.9 55.5 47.0 8.5 HEAD CIRC. (Cms.) 34.6 2.3 18.0 31.0 7.0 APGAR (1 Min.) 3.2 1.8 6 1 5 APGAR (5 Min.) 5.6 1.2 6 3 3 TEST AGE (Hrs.) 77.5 10.7 95 65 30 44
PATIENT OR VOLUNTEER CONSENT TO SPECIAL PROCEDURE
Date ____ Time P.M.
I authorize the performance upon ______(myself or name of patient) of the following procedure: electrocardiogram and recording of suck- (state nature and extent) ing responses on a commercial pacifier as part of an investigation entitled "Cardiac and Sucking Responses in the Human Neonate".
This procedure is to be performed by, or under the direction of Dr. Leandro Cordero. He is authorized to use the services of others in the performance of this procedure as he deems necessary.
The nature and purpose of the procedure, the known risks involved, and the possibility of complications have been explained to me, and I understand them. I fully understand that the study to be performed is experimental and unproven by medical experience.
I understand that the known risks are:
NONE
Signed: (Patient or person author- ized to consent for patient)
Witness ______
Witness (Investigator)
FIGURE 1 45 premature infant, the identical procedure was employed if the infant was in an open crib. If it was still in an isolette in the Neonatal
Intensive Care Unit, the entire isolette was wheeled to the testing room, and the electrodes applied through one of the portholes.
The electrodes on the infant led to a Grass Model 7 ink-writing oscillograph, yielding a continuous EKG on the polygraph paper. A stimulus signal marker (voltage-change type) was used to simultane ously record the onset and duration of all stimuli on the polygraph printout. A Grass cardiotachometer (Model 7P4AO) instantaneously converted each r-r cycle interval into a rate-per-minute score, and recorded this level on a different channel of the polygraph, allow ing for continuous monitoring of heart rate and its variability. In order to record the rhythm of non-nutritive sucking, a closed-air system employing a commercial pacifier was used. The pacifier was connected to a thin polyethylene tube, which led to a pressure transducer. The entire system was saline-filled, so that changes in liquid pressure, through the transducer, were transformed into electrical impulses and fed into the Grass Model 7 polygraph. The result of this arrangement was a printout on one channel of the poly graph paper containing upward pen deflections for every positive pressure applied to the pacifier by the infant. The entire system was calibrated daily with a manometer, so that exact readings of the pressure of any activity could be made from the polygraph paper printout.
To summarize, with these recording techniques a polygraph print out was obtained from each infant, containing on different channels 46 neonatal EKG, continuous beat-by-beat cardiac rate, an indication of the onset and duration of any stimulation, and a measure of non-nutri tive sucking activity.
Once all of the equipment was checked and the infant had quieted down, with its resting heart rate stabilized and over behavior meet ing the criteria of quiet sleep (see next section), the experiment was begun.
The following procedures were followed sequentially:
1. A series of ten auditory stimuli, each one of five sec
ond duration, with an intertrial interval of 45 seconds
between stimuli was presented. The stimulus originated
in an instrument designed for testing newborn hearing,
a Rudmose Warblet 3000. This device produced a warbled
tone of 3000 cps, with FM deviation of +_ 150 cps at a
30-40 cps rate, and a maximum sound pressure level of
100 ^ 1 db when held 9-10 inches from the subject's ear.
The axis of the Warblet was kept continuous with that of
the infant's auditory canal. The voltage change signal
marker was engaged simultaneously for the entire dura
tion of the stimulus.
2. A three minute rest period occurred after the series of
auditory stimuli.
3. A series of ten tactile stimuli of approximately two
second duration, with an intertrial interval of 45 sec
onds between stimuli was presented. The stimulus con
sisted of a single nylon filament touched to the infantfs 47
cheek, and moved from the corner of the mouth back to
ward the infant's ear. The voltage change signal mark
er was engaged simultaneously for the entire duration
of the stimulus.
4. A three to five minute rest period was observed, after
which the infant was aroused from its light sleep with
stroking of the cheek, tapping of the foot, etc.
5. The infant was then presented the pacifier, recently
dipped in a 10% glucose solution, and allowed from 10-20
minutes free sucking time.
Following the recording of sucking behavior, the equipment was turned off, the electrodes were removed, and the infant was returned to the nursery.
METHODOLOGICAL ISSUES
As with any study involving the human infant, the problem of state was considered early in the planning stage. State has been shown to affect both the quantity and directionality of the cardiac response (Lewis et al., 1969), although this may work indirectly through the effect of state on prestimulus heart rate level (Stein- schneider, 1971). In any case, state must be considered and control led, so that any heart rate reaction is a function of stimulus proc essing and not an artifact of movement or state change. Thus, the heart rate data of this study were obtained while the infant was in a state of quiet sleep. Quiet sleep was defined by the following 5 criteria (as in Hock, 1971): 1. Eyes closed.
2. Regular respiration.
3. Few overt movements (only slight).
4. Resting heart rate maintaining a fairly constant baseline
(disregarding natural variability).
5. Absence of observable rapid eye movements.
Quiet sleep was considered the ideal state for several reasons. First,
it is easily defined without requiring the measurement of several phys
iological functions. Second, newborns are asleep about 70% of the
time, and it is probably easier to find and keep an infant asleep than
to keep him awake. In order to find the infant during a period in
which he was asleep, and likely to remain so throughout the procedure,
the infants were always tested between one and two hours after a feed
ing (usually the 10:00 A.M. or 2:00 P.M. feeding).
The particular stimuli employed in the heart rate portion of the
study were chosen because they were identical to those used by Hock
(1971), therefore making the results obtained here comparable to those
in her study. The reasons stated by Hock (1971) for the use of the
particular auditory stimulus involved were the greater responses evi
dences in past studies to that level and complexity of tone, and the need for a high db level due to the fairly large amount of background noise.
It was decided not to include infants younger than 40 hours of
age because of their decreased responsivity to stimulation and over all behavioral depression due to the lingering effects of maternal medication (Kron et al., 1966), labor, and delivery. Further, male 49 infants were not tested sooner than 24 hours after circumcision, since any irritability resulting from this procedure may have affected the results, particularly in the tactile modality. CHAPTER IV
ANALYSIS OF THE DATA
This chapter is divided into two sections, covering in succession
the reduction and statistical analysis of the heart rate data and the preliminary preparation and statistical analysis of the sucking data.
REDUCTION AND ANALYSIS OF THE HEART RATE DATA
The first task of the heart rate data reduction was to convert the information from the cardiotachometer channel of the polygraph printout into measures that were meaningful and amenable to statisti cal analysis. After reviewing the many complex measures employed in various cardiac response studies, 19 scores were chosen that were ad equate to define responsivity for the purposes of this study. These were:
1. Resting heart rate level, defined as the mean of all
heart rate scores occurring in a 20 second period prior
to any stimulation.
2. Resting heart rate variability, defined as the stand
ard deviation of all heart rate scores occurring in a 20
second period prior to any stimulation.
3. Prestimulus level, defined as the mean of all heart rate
scores occurring in the 5 second period prior to a stim
ulation. 51
4. Prestimulus variability, defined as the standard devia
tion of all heart rate scores occurring in the 5 second
period prior to a stimulation.
5. Stimulus level, defined as the mean of all heart rate
scores occurring in the 5 second period during a stimu
lation.
6 . Stimulus variability, defined as the standard deviation
of all heart rate scores occurring in the 5 second peri
od during a stimulation.
7. Poststimulus level, defined as the mean of all heart
rate scores occurring in the 5 second period following
a stimulation.
8 . Poststimulus variability, defined as the standard de
viation of all heart rate scores occurring in the 5
second period following a stimulation.
9. Peak magnitude, defined as the fastest single heart rate
occurring anywhere within 15 seconds of stimulus onset.
10. Latency to peak magnitude, defined as the number of sec
onds from stimulus onset to peak magnitude.
11. Trough magnitude, defined as the slowest single heart
rate occurring anywhere between the peak magnitude and
30 seconds after stimulus onset.
12. Latency to trough magnitude, defined as the number of
seconds between stimulus onset and trough magnitude.
13. Prestimulus magnitude, defined as the last single heart
rate prior to stimulus onset. 52
14. Delta P, defined as the amount of change between pre
stimulus magnitude and peak magnitude.
15. Delta T, defined as the amount of change from prestim
ulus magnitude to trough magnitude.
16. Cardiac range, defined as the amount of change from
peak magnitude to trough magnitude.
17. Stimulus level minus prestimulus level, a change score
defined as the difference between variable #5 and var
iable #3.
18. Stimulus level minus poaststimulus level, a change
score defined as the difference between variable #5
and variable #3.
19. Poststimulus level minus prestimulus level, a change
score defined as the difference between variable #7
and variable #3.
All of the above measures were obtained from the raw data pre sented on the polygraph printout. All means and standard deviations were obtained by feeding the heart rate scores into a Hewlett-Packard
Programmable Calculator. The end result of this data reduction proc ess was 19 scores for each stimulation in both modalities. In the course of the experiment it was noted that occasionally an infant would show a startle response to a stimulation (flinching of the head, movement of the arms or body). Since heart rate changes under these conditions were likely to be a function of bodily movement and not the result of information processing, it was felt that such trials should not be included in the analysis. Therefore, all records were divided 53 into two halves, the first half containing trials one through five and the second half containing trials six through ten. Any trial in which an infant exhibited a startle response was discarded, and in the alter nate half one trial was chosen at random and also discarded. On the records in which there was no startle response on any trial, a trial was dropped at random from both the first and second half. Thus, in both modalities two trials were dropped from each infant's record, re sulting in eight auditory trials and eight tactile trials being in cluded in the analysis.
The first step of the statistical analysis was the construction from the reduced data of an average response for each group in both modalities, collapsed over trials, and defined by the nineteen vari ables described above. Based on this average response nineteen one way ANOVAS across the six groups, with post-hoc compairsons of signif icant differences, were performed on both the auditory and tactile data. A correlational analysis was done yielding one matrix per group for the auditory data, one matrix per group for the tactile data, and one overall matrix across groups in each modality, thus allowing for a consideration of significant relationships among the nineteen heart rate variables.
An habituation analysis was done for each group in each modality.
This consisted of seventeen one-way ANOVAS, one each for variables three through nineteen and looking at changes over trials one through eight. This procedure allowed for a consideration of any significant change in responsivity over trials for each group in both modalities.
Finally, a stepwise regression analysis was done across all in fants (N=60) in each modality. This analysis considered nine subject 54 descriptive factors and their value in predicting the nineteen depend ent responsivity variables in each modality. The nine descriptive factors were: gestational age at test, birth weight, length, head cir cumference, one minute APGAR, five minute APGAR, test age, sex,, and group (healthy full term, premature, high risk).
PREPARATION AND ANALYSIS OF THE SUCKING DATA
Data on sucking behavior was obtained from the polygraph records, which were divided into two minute segments and scored for the follow ing measures commonly used in studying non-nutritive sucking.
1. Burst time, defined as the mean length of all burst of
sucking occurring in a two minute period.
2. Burst time variability, defined as the standard devia
tion of all bursts of sucking occurring in a two minute
period.
3. Rest time, defined as the mean length of all rest peri
ods following a burst in a two minute period.
4. Rest time variability, defined as the standard deviation
of all rest periods following a burst in a two minute
period.
5. Number of sucks per burst, defined as the mean number of
sucks occurring in a burst in a two minute period.
6 . Variability of number of sucks per burst, defined as the
standard deviation of all numbers of sucks occurring in
a burst in a two minute period.
7. Amplitude of sucks, defined as the mean pressure of all
sucks occurring in all bursts in a two minute period. 55
8 . Variability of amplitude of sucks, defined as the standard
deviation of all sucks occurring in all bursts in a two
minute period.
9. Rate of sucking, defined as the mean rate in sucks per
second occurring in all bursts in a two minute period.
10. Variability of rate of sucking, defined as the standard
deviation of all rates of sucks per second occurring in
all bursts in a two minute period.
11. Total time sucking, defined as the total time spent in
bursts of sucking in a two minute period.
12. Total time resting, defined as the total time spent in
nonburst activity un a two minute period.
13. Total number of sucks, defined as the total number of
sucks in a two minute period.
It is noted here that a burst is defined as a series of sucks in a
short period of time. The end result of the reduction of the sucking data was the above thirteen scores defining the non-nutritive sucking behavior of each infant. As with the heart rate data, all means and standard deviations were obtained by feeding the raw scores into a
Hewlett-Packard Programmable Calculator.
The first step of the statistical analysis was the construction from the reduced data of an average performance for each group, de fined by the thirteen variables.
Based on this average performance, group differences were consid ered by performing thirteen one-way ANOVAS, one on each variable, a- cross the groups with post hoc tests for places of significant differ ences . 56
A correlational analysis yielded six matrices, one for each group and one overall matrix across groups, thus allowing for a consideration of significant relationships among the thirteen sucking variables.
A stepwise regression analysis was done across all infants (N=60) determining the value of the nine subject descriptive factors previ ously mentioned in predicting the thirteen dependent measures of non nutritive sucking behavior.
Finally, the thirteen measures of sucking behavior were correlated with the nineteen measures of heart rate responsivity to consider sig nificant relationships between the two types of behavior. This was done separately for each group, as well as over all 60 infants. CHAPTER V
RESULTS
This chapter is divided into seven sections covering in succes
sion: the analysis of group differences on the auditory cardiac data,
the analysis of group differences on the tactile cardiac data, the
correlational analyses on the auditory and tactile cardiac data, the
analysis of responsivity change over trials, the analysis of group
differences and the correlational analysis on the non-nutritive suck
ing data, the stepwise regression analyses on the cardiac and non
nutritive sucking data, and finally the correlational analyses relat
ing the cardiac and sucking data.
ANALYSIS OF GROUP DIFFERENCES ON THE AUDITORY CARDIAC DATA
The average cardiac response on the 19 variables in the auditory modality for all six groups is listed in Tables 4 through 9. That the average cardiac response to the auditory stimulus was acceleratory is
indicated by variables 14 and 17, the change scores reflecting the difference between the peak and prestimulus magnitudes and the differ ence between the stimulus and poststimulus levels respectively. Vari able 14 (Delta P) ranged from 14 and 17 beats per minute (BPM) for the healthy full term infants to 8 and 11 BPM for the premature infants,
57 and 7 and 10 BPM for the high risk infants. Variable 17 (stimulus
level - prestimulus level) ranged from 5 and 8 BPM for the healthy
full term infants, to 2 and 4 BPM for the premature infants, and 2 BPM
for both groups of high risk full term infants. A rebound decelera
tion is reflected in the scores on variable 15 (Delta T), which is the
difference between the prestimulus and trough magnitudes. Scores
ranged from 10 and 12 BPM for all groups on this variable. Variable
10, latency to peak magnitude, indicated that the peak of the acceler
ation was reached in approximately 6 seconds for the healthy full term
infants, and approximately 7 seconds for both the premature and high
risk full term infants. Variable 12, latency to trough magnitude, in
dicated that the depth of the rebound deceleration was reached in
approximately 17 seconds for all groups.
The summary of the one-way analyses of variance across the
groups on the auditory cardiac data is contained in Table 10. Signif
icant differences across the groups were obtained for 15 of the 19
variables. No differences were noted for variable 10, latency to peak
magnitude, variable 12, latency to trough magnitude, variable 15,
Delta T, and variable 18, stimulus minus poststimulus level. Follow
ing the analyses of variance, post-hoc tests of significance were per
formed to identify those groups that could be differentiated from one
another on each of the 19 variables. Table 11 contains the summary of
these post-hoc tests of significance. For variable 1, resting heart
rate level, the hierarchy of homogeneous subsets, sets within which no groups were significantly different, ranged from a high for premature males, to premature females, high risk males, full term males, and high risk females, to a low for full term and high risk females. For variable 2, resting heart rate variability, the hierarchy ran from
full term males and females and premature females, to full term males and high risk males and females, to a low for premature males. For variable 3, prestimulus level, 5, stimulus level, 7, poststimulus
level, 9, peak magnitude, 11, trough magnitude, and 13, poststimulus magnitude, the hierarchy was essentially the same as for variable 1.
For variable 4, prestimulus variability, the hierarchy ran from full term males and females, to full term and high risk females, down to a low for both premature and high risk males and females. For vari ables 6 and 8, stimulus and poststimulus variability, the grouping was essentially the same as for variable 4. For variable 10, as for vari ables 12, 15, and 18, no differences existed between the groups. For variable 14, Delta P, the heirarchy ran from a high for the healthy full term males and females, to the premature and high risk females, to the premature males and high risk females, down to a low for the premature and high risk males. For variable 16, cardiac range, the order was a high for full term females, to full term males and pre mature and high risk females, down to a low for premature and high risk males. For variable 17, stimulus minus prestimulus level, the order was from a high for full term females, to full term males and premature females, to a low for both premature and high risk males and females. For variable 19, poststimulus minus prestimulus level, the only differences were for the full term females, who showed sig nificantly larger changes than all other groups. 60
Due to the differences on resting heart rate level between the groups, and in deference to the Law of Initial Value (Wilder, 1967), an analysis of covariance was performed across the groups for 16 of the variables, employing variable 3, prestimulus level, as the covari ant, and therefore "correcting" for differences between the groups on the level of organ functioning prior to stimulation. The results of this analysis are listed in Table 12. There was no change in the sig nificance of the group effects on any of the variables except vari able 13, prestimulus magnitude, which was expected. The hierarchy of subsets on the variables in which significant group effects existed were identical to those reported for the one-way analyses of variance.
ANALYSIS OF GROUP DIFFERENCES ON THE TACTILE CARDIAC DATA
The average cardiac response on the 19 variables in the tactile modality for all six groups is listed in Tables 13 through 18. That the average cardiac response to the tactile stimulus was acceleratory is indicated by variables 14 and 17, as in the auditory modality.
Variable 14 ranged from 11 and 12 BPM for the healthy full term in fants, to 8 and 10 BPM for the high risk full term infants, and 7 and 9 BPM for the premature infants. Variable 17 ranged from 4 BPM for both groups of full term infants, to 2 BPM for both groups of high risk infants, and 1 and 2 BPM for the premature infants. A rebound deceleration is reflected in the scores on variable 15, the difference between the prestimulus and trough magnitude, which ranged from 12 and 13 BPM for the healthy full term infants, to 8 and 10 BPM for the high risk infants, and 9 BPM for both groups of premature infants. 61
Variable 10, latency to peak magnitude, indicated that the peak of the
acceleration was reached in approximately 5 seconds for the full term
infants, 6 and 7 seconds for the high risk infants, and 7 and 8 sec
onds for the premature infants. Variable 12, latency to trough magni
tude, indicated that the depth of the rebound deceleration was reach
ed in 14 seconds for the full term infants, 16 and 18 seconds for the
premature infants, and 15 and 19 seconds for the high risk infants.
The summary of the one-way analyses of variance across the groups
on the tactile cardiac data is contained in Table 19. Significant dif
ferences across the groups were obtained on all 19 variables. Table 20
contains the summary of the post-hoc tests of significance intended to
identify the hierarchy of homogeneous subsets. For variables 1 and 2,
resting heart rate level and variability, the hierarchy is, of course,
identical to that reported for the auditory cardiac data, since those measures were taken prior to all stimulation. For variable 3, pre
stimulus level, the hierarchy ranged from a high for both groups of premature infants, to the healthy and high risk full term males, to a low for the healthy and high risk full term females. For variable 4, prestimulus variability, the hierarchy ranged from a high for both groups of healthy full term infants, to the healthy and high risk full term females, to both groups of premature infants and the high risk males. For variables 5, 7, 9, 11, and 13, the hierarchy was essen tially identical to that indicated for variable 3. Variables 6 and 8 ranged in a manner identical to that shown for variable 4. For vari able 10, latency to peak magnitude, the order was both groups of pre mature infants and high risk females, to both groups of high risk 62
infants and premature males, to the high risk males and full term fe males, down to a low for both groups of healthy full term infants.
For variable 12, latency to trough magnitude, the order was similar to
that listed for variable 10. For variable 14, Delta P, the greatest accelerations were for both groups of healthy full term infants and
the premature and high risk females, to both groups of high risk in
fants and premature females, to a low for both groups of premature in ants and the high risk males. For variable 15, Delta T, the greatest rebound decelerations were noted in both groups of full term infants and the high risk males, down to a low for both groups of premature infants and both groups of high risk infants. For variable 16, car diac range, the greatest overall range of cardiac functioning was noted for both groups of healthy full term infants, with both groups of premature and both groups of high risk infants combining in a group with decreased range. The groupings for variable 17 were simi lar to that for variable 16. For variable 18, the greatest changes were again noted for both groups of healthy full term infants, to the healthy full term females and high risk males, down to a low for both groups of premature infants and the high risk females. The groupings on variable 19 were essentially identical to those on variables 10 and 12, the two latency scores, indicating highest poststimulus levels for those infants slower in responding.
For the reasons stated in the review of the auditory cardiac re sults, an analysis of covariance was performed across the groups for
16 of the variables, employing variable 3, prestimulus level, as the variant in order to "correct" for level of organ functioning prior to 63
stimulation. The results of this analysis are listed in Table 21.
There was no change in the significance of the group effects on 15 of the 17 variables. Variable 13, prestimulus magnitude, showed no group effect, which would be expected. Variable 14, Delta P, also moved to insignificance, suggesting that the amount of acceleration in response to the tactile stimulus was a function of prestimulus level. The hi erarchy of subsets on the variables for which significant group effects remained were identical to those reported following the one-way analy ses of variance.
CORRELATIONAL ANALYSES ON THE AUDITORY AND TACTILE CARDIAC DATA
The results of the correlational analysis for all 19 variables across all 60 infants for the auditory cardiac data are listed in Ta ble 22. As would be expected, all measures of heart rate level, vari ables 1, 3, 5, and 7, were significantly related at the .01 level.
All of these measures were also significantly related to peak and trough magnitude (variables 11 and 13) as well as prestimulus magnitude (var iable 13). All measures of heart rate variability (variables 2, 4, 6, and 8) were related at the .01 level. All of these variability meas ures were significantly related to variable 16, cardiac range, whereas none of the measures of heart rate level except variable 11 were re lated to the cardiac range score. Further, variable 1, resting heart rate level, was only mildly related to variable 14, Delta P, and unre lated to trough magnitude or any of the difference scores (variables
17, 18, and 19). Variables 1 and 2, resting heart rate level and variability respectively, were unrelated, suggesting that for the 64 ranges of both variables available with this sample of infants, level and variability acted as independent factors. The two latency scores, variables 10 and 12, were significantly related at the .01 level.
Both latency scores were also related to variables 18 and 19, indi cating that the slower responders were still accelerating in heart rate into the poststimulus period. Variable 14, Delta P, which is the measure of acceleration, was significantly related to variable 13, prestimulus magnitude, as expected from the Law of Initial Value, but was also significantly related to the variability scores on variables
2, 4, 6, and 8. Finally, variable 15, Delta T, the measure of rebound deceleration, was most significantly related to variable 8, a vari ability measure. The results of the correlational analysis on the tactile cardiac data are contained in Table 23. The vast majority of the relationships between the variables were identical in signifi cance and direction to those reviewed for the auditory data.
ANALYSIS OF RESPONSIVITY CHANGE OVER TRIALS
The results of the 17 one-way analyses of variance over the eight trials for the auditory cardiac data are listed in Table 24.
This procedure was done to allow for a consideration of any signifi cant changes in responsivity over trials for each group. The fact that prestimulus level, variable 3, and prestimulus magnitude, vari able 13, did not change significantly from trial 1 through trial 8 would allow for a conclusion that any drop in acceleration over trials was a function of repeated stimulation and not an artifact due to changes in prestimulus heart rate. A review of Table 24 clearly indicates that there was no change in responsivity over any of the
trials for any group in the auditory modality, other than a trend for
the latency to trough magnitude to decrease over trials for both groups of healthy full term infants. Statistically, the post-hoc tests of significance indicated that for all groups none of the 17 variables considered changed over trials; that is, all eight trials were statistically identical. The results of the 17 one-way analyses of variance over the eight trials for the tactile cardiac data are listed in Table 25. Again, no significant differences on any of the
17 variables considered were shown over the eight trials, and all trials in the tactile modality were statistically identical.
ANALYSIS OF GROUP DIFFERENCES AND CORRELATIONAL ANALYSIS ON THE NON-NUTRITIVE SUCKING DATA
The average non-nutritive sucking performance on the 13 vari ables for all six groups is listed in Tables 26 through 31. The aver age burst time ranged from a high of 7 and 8 seconds for the healthy full term infants, to 6 and 7 seconds for the high risk infants, down to 5 and 6 seconds for the premature infants. Rest time averaged be tween 5 and 6 seconds for all groups of infants. The number of sucks per burst ranged from a high of 12 and 13 for the healthy full term infants, to 9 and 11 for the high risks infants, down to 8 and 10 sucks per burst for the premature infants. The average pressure of sucks within a burst ranged from a high of 59 and 66 mm Hg for the healthy full term infants, down to 42 and 48 mm Hg for the premature infants. The rate of sucking varied from 1.8 sucks per second for both grour.s of healthy full term infants to 1.5 or 1.6 for both the 66 premature and high risk infants. The total time spent sucking within
the two minute period fell between 50 and 70 seconds for all groups.
The total number of sucks within the two minute period fell between 86 and 110 sucks for all six groups of infants.
The summary of the one-way analyses of variance on each of the
13 variables across the groups for the non-nutritive sucking data is listed in Table 31. The only variable to reach a significant group effect was variable 9, rate of sucking. Post-hoc tests of signifi cance indicated that the hierarchy of homogeneous subsets ranged from a high for both groups of healthy full term infants, to a low for both groups of premature and high risk infants. Thus, both premature and high risk infants were significantly reduced in their rate of sucking relative to the healthy full term infants.
The summary of the correlational analysis relating to 13 vari ables of non-nutritive sucking data across all 60 infants is listed in Table 33. Variables 1 and 2 were related at the .01 level, indi cating that the greater the burst length, the more likely the bursts were to vary one from another. Variables 1 and 3 were positively re lated at the .01 level, indicating that longer bursts were associated with longer rest periods. The relation of variables 1 and 5 was to be expected as increased number of sucks per burst increased the burst length. A mild tendency relating variables 1 and 7 suggested a tend ency for longer bursts to be associated with higher pressure sucking.
Finally, variable 1 was related significantly to variables 11, 12, and
13, indicating that as burst time increased, so did total time sucking and total number of sucks, while total time resting decreased. The 67
relationship between variables 2, 5, and 6 suggested that variable
burst time related to a variable number of sucks per burst, greater
time sucking, greater total number of sucks, and decreased rest time.
Variables 3 and 4 were related significantly, indicating that for
•greater rest periods, more variability in their length was evident.
A significant correlation between variables 3 and 5 suggested that as
number of sucks per burst increased, so did the resting time. Vari
ables 5 and 6 indicated that increased number of sucks per burst were
related to increased variability on that same measure. Number of
sucks per burst also correlated with total time sucking, total number
of sucks, and decreased total time resting. Also, a mild relationship
existed between number of sucks per burst (variable 5) and rate of
sucking (variable 9) and pressure of sucking (variable 7). Variables
7 and 8 indicated that at the upper ranges of pressure, more vari
ability existed on the amplitude measure. Finally, variables 11, 12,
and 13 were all related, as expected, with total time sucking and
total number of sucks related positively to one another and negatively
to total time resting.
STEPWISE REGRESSION ANALYSES ON THE CARDIAC AND NON-NUTRITIVE SUCKING DATA
The summary of the stepwise regression analysis relating nine
predictive factors to the 19 variables of auditory cardiac data is
listed in Table 34. Only the two most significant predictors are
listed for each variable. For heart rate variables 1, 3, 5, 7, 9, 11,
and 13 the two most significant predictors were length and sex (fac
tors 3 and 8 respectively). For variables 2, 4, 6, and 8, the heart 68
rate variability measures, the most significant predictors were head
circumference, 5 minute Apgar score, group affiliation, and birth weight. For variable 10, latency to peak magnitude, the most signif
icant predictors were gestational age at test and 1 minute Apgar
score. For variable 12, latency to trough magnitude, the significant predictors were 1 minute and 5 minute Apgar. For variables 14, 15,
and 16, the significant predictors were 5 minute Apgar, sex, and group affiliation, length, and gestational age at test.
The summary of the stepwise regression analysis on the tactile cardiac data is listed in Table 35. As for the auditory data, the most significant predictors for variables 1, 3, 5, 7, 9, 11, and 13, were length and sex. For variables 2 and 4, the predictors were sex and group affiliation. For variables 6 and 8, the significant pre dictors were gestational age at test, 5 minute Apgar, and head cir cumference. For variable 10, the predictors were gestational age at test and group affiliation. For variable 12, the predictive factors were 1 minute Apgar and test age. For variables 14, 15, and 16, the most significant factors were 5 minute Apgar and head circumference.
For the change scores, variables 17, 18, and 19, the factors most predictive of performance were gestational age at test, sex, group affiliation, and 1 minute Apgar.
The summary of the stepwise regression analysis on the 13 vari ables of non-nutritive sucking behavior is listed in Table 36. For variable 1, burst time, the significant predictors were gestational age at test and 1 minute Apgar. For variable 3, rest time, the pre dictors were sex and birth weight. For variable 5, number of sucks per burst, the most significant predictors were again gestational age
at test and 1 minute Apgar. The greatest predictors of variable 7,
amplitude of sucks, were birth weight and head circumference. For variable 9, rate of sucking, the greatest predictive values lie in
group affiliation and head circumference. On variable 11, total time
sucking, the predictors were group affiliation and 1 minute Apgar.
On variable 12, total time resting, the significant predictors were 5 minute Apgar and gestational age at test. Finally, on variable 13,
total number of sucks, the predictors were head circumference and 1 minute Apgar.
CORRELATIONAL ANALYSES RELATING THE CARDIAC AND SUCKING DATA
The results of the correlational analysis relating the 19 vari ables of auditory cardiac data to the 13 variables of non-nutritive sucking data are listed in Table 37. All measures of heart rate level variables 1, 3, 5, and 7, as well as peak, trough, and prestimulus magnitude (9, 11, and 13) were significantly inversely related to suck ing amplitude and its variability (variables 7 and 8). Cardiac range, variable 16, was positively related at the .05 level to the amplitude of sucking measure and its variability. Stimulus heart rate variabil ity (variable 6) was positively related to amplitude of sucking, am plitude variability, and rate of sucking (variables 7, 8, and 9).
Resting heart rate variability (2) was inversely related at the .05 level to variability in the rate of sucking (10). All other correla tions were insignificant. 70
The results of the correlational analysis relating the 19 vari ables of tactile cardiac data to the 13 variables of non-nutritive sucking data are listed in Table 38. As with the auditory cardiac data, all measures of heart rate level, variables 1, 3, 5, and 7, as well as peak, trough, and prestimulus magnitude (9, 11, and 13), were significantly inversely related to sucking amplitude and its vari ability (variables 7 and 8). Cardiac range (variable 16) was no long er related to any of the sucking measures. Stimulus heart rate vari ability (variable 6) was related only to the variability in the am plitude of sucking (8). Finally, resting heart rate variability (2) was again inversely related to the variability in the rate of suck ing (10). All other correlations were insignificant. 71
TABLE 4
HEALTHY FULL TERM MALES AVERAGE CARDIAC RESPONSE AUDITORY MODALITY
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 122.7 17.4 144.0 90.3 53.7 2 4.6 1.3 6.9 2.5 4.4 3 121.7 16.7 149.8 79.3 70.5 4 4.0 2.6 12.6 1.0 11.6 5 126.8 16.5 151.2 87.3 63.9 6 5.6 3.2 16.0 0.8 15.2 7 125.8 18.9 158.9 76.1 82.8 8 4.8 3.2 19.7 1.0 18.7 9 135.8 15.8 162.0 96.0 66.0 10 6.5 3.8 15.0 1.0 15.0 11 112.4 18.3 136.0 66.0 70.0 12 17.0 6.1 30.0 6.0 24.0 13 121.5 16.9 148.0 70.0 78.0 14 14.3 10.1 45.0 1.0 44.0 15 9.9 7.0 32.0 0.0 32.0 16 23.7 11.1 53.0 8.0 45.0 17 5.1 6.0 24.8 -6.6 31.4 18 1.0 7.6 16.6 -20.2 36.8 19 4.0 8.8 28.2 -1 1.8 40.0 72
TABLE 5
HEALTHY FULL TERM FEMALES AVERAGE CARDIAC RESPONSE AUDITORY MODALITY
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 115.6 10.8 129.8 93.2 36.6 2 4.9 2.4 9.0 1.6 7.4 3 114.2 11.7 134.8 87.5 47.3 4 3.4 2.8 20.0 0.8 19.2 5 122.8 10.0 143.5 101.2 42.3 6 6 . 1 3.8 17.2 0.5 16.7 7 121.8 11.9 144.7 90.3 54.4 8 4.8 2.8 14.1 0.6 13.5 9 132.0 9.5 152.0 113.0 39.0 10 5.8 2.8 13.0 1.0 12.0 11 104.4 13.2 128.0 73.0 55.0 12 16.3 5.6 26.0 6.0 20.0 13 114.9 12.2 136.0 84.0 52.0 14 16.8 10.8 42.0 0.0 42.0 15 11.2 7.9 42.0 0.0 42.0 16 28.0 11.8 54.0 6.0 48.0 17 8.4 7.9 31.9 -5.1 37.0 18 1.0 6 .3 15.2 -14.3 29.5 19 7.4 10.1 34.3 -9.6 43.9 73
TABLE 6
PREMATURE MALES AVERAGE CARDIAC RESPONSE AUDITORY MODALITY
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 145.8 14.7 163.2 116.9 46.3 2 3.5 1.1 5.6 1.4 4.2 3 144.8 15.8 177.8 103.8 74.0 4 2.5 1.6 7.9 0.4 7.5 5 147.0 15.9 175.0 106.9 68. 1 6 2.5 1.4 7.3 0.5 6.8 7 147.6 16.1 172.3 105.8 66.5 8 3.0 2.6 13.9 0.1 13.8 9 153.2 15.0 179.0 116.0 63.0 10 7.5 4.9 16.0 1.0 15.0 1 1 137.4 17.6 170.0 100.0 70.0 12 16.9 6.3 29.0 4.0 25.0 13 145.1 15.3 178.0 105.0 73.0 14 7.9 4.5 21.0 0.0 21.0 15 9.2 6.3 26.0 0.0 26.0 16 17.2 7.1 36.0 5.0 31.0 17 2.1 4.5 11.3 -12.3 23.6 18 -0.6 5.1 14.5 -14.5 29.0 19 2.8 5.9 17.5 -10.5 28.0 74
TABLE 7
PREMATURE FEMALES AVERAGE CARDIAC RESPONSE AUDITORY MODALITY
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 136.6 17.1 158.5 104.0 54.5 2 5.1 1.5 7.3 1.8 5.5 3 135.1 15.9 176.8 100.5 76.3 4 2.6 1.7 8.2 0.4 7.8 5 139.0 14.0 176.8 112.5 64.3 6 3.4 2.5 12.4 0.6 11.8 7 139.5 14.5 171.4 106.7 64.7 8 3.7 2.7 15.5 0.6 14.9 9 147.0 13.3 180.0 120.0 60.0 10 7.3 3.9 15.0 1.0 14.0 11 123.7 17.4 156.0 90.0 66.0 12 17.5 7.2 30.0 5.0 25.0 13 135.3 15.9 178.0 102.0 76.0 14 11.6 8.3 37.0 0.0 37.0 15 11.9 8.6 44.0 0.0 44.0 16 23.4 10.5 48.0 6.0 42.0 17 3.8 6.0 19.1 -10.9 30.0 18 -0.5 6.9 16.6 -17.9 34.5 19 4.3 9.3 29.4 -16.6 46.0 75
TABLE 8
HIGH RISK FULL TERM MALES AVERAGE CARDIAC RESPONSE AUDITORY MODALITY
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 129.7 14.2 149.0 104.5 44.5 2 4.1 2.3 8.1 0.5 7.6 3 128.3 14.4 151.8 101.7 50.1 4 2.7 2.1 9.4 0.3 9.1 5 130.2 14.9 155.2 102.3 52.9 6 2.6 1.9 9.2 0.0 9.2 7 130.5 14.7 152.6 101.9 50.7 8 2.7 2.4 13.8 0.4 13.4 9 135.7 15.7 157.0 104.0 53.0 10 6.9 4.2 15.0 1.0 14.0 11 118.7 10.5 141.0 89.0 52.0 12 16.3 6.7 30.0 3.0 27.0 13 129.0 14.2 154.0 102.0 52.0 14 6.7 5.8 25.0 0.0 25.0 15 10.2 9.6 38.0 0.0 38.0 16 16.9 10.8 41.0 2.0 39.0 17 1.9 4.7 16.7 -10.8 27.5 18 -0.3 4.9 14.2 -10.0 24.2 19 2.2 6.8 26.6 -13.8 40.4 76
TABLE 9
HIGH RISK FULL TERM FEMALES AVERAGE CARDIAC RESPONSE AUDITORY MODALITY
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 118.7 7.9 128.7 105.3 23.4 2 . 4.1 1.6 6.8 1.3 5.5 3 118.7 14.1 152.6 94.4 58.2 4 3.0 2.1 13.1 0.5 12.6 5 120.9 13.7 158.2 98.4 59.8 6 4.1 3.2 23.9 0.6 23.3 7 120.3 14.3 151.5 91.6 59.9 8 3.7 2.6 14.1 0.4 13.7 9 128.9 12.8 161.0 108.0 53.0 10 6.7 4.6 15.0 1.0 14.0 11 108.5 15.5 149.0 84.0 65.0 12 18. 1 6.8 30.0 2.0 28.0 13 1 18.6 14.5 156.0 87.0 69.0 14 10.1 7.7 32.0 0.0 32.0 15 10.9 8.5 33.0 0.0 33.0 16 21.1 8.8 42.0 6.0 36.0 17 2.2 5.0 15.9 -18.2 34.1 18 0.6 6.4 18.1 -19.9 38.0 19 1.5 8.9 34.1 -24.3 58.4 77
TABLE 10
SUMMARY OF ONE-WAY ANOVAS ACROSS THE GROUPS FOR THE AUDITORY CARDIAC DATA
VAR.NO.D.F.F-RATIO F PROB.
1 5,474 52.85 .0001 2 5,474 8.61 .0001 3 5,474 46.43 .0001 4 5,474 5.21 .0001 5 5,474 39.01 .0001 6 5,474 22.22 .0001 7 5,474 39.60 .0001 8 5,474 7.67 .0001 9 5,474 36.03 .0001 10 5,474 1.85 NS 11 5,474 46.29 .0001 12 5,474 .98 NS 13 5,474 46.19 .0001 14 5,474 17.33 .0001 15 5,474 1.15 NS 16 5,474 14.03 .0001 17 5,474 14.78 .0001 18 5,474 1.27 NS 19 5,474 4.83 .0001
NS = Not Significant 78
TABLE 11 POST-HOC TESTS OF SIGNIFICANCE FOR ONE-WAY ANOVAS ACROSS THE GROUPS ON AUDITORY CARDIAC DATA
VARIANCE NUMBER HOMOGENEOUS SUBSETS
1 2,6< 6 ,1 < 5< 4 <3 2 3 < 6 , 5 , 1 < 1,2,4 3 2,6<6,1< 5<4< 3 4 3,4,5,6< 6 ,2< 2,1 5 6,2< 2,1 < 1,5 <4 < 3 6 3,5,4<4,6< 1,2 7 6,2< 2,1 < 5 < 4 < 3 8 5,3,6,4< 2, 1 9 6,2<2,5,1<4<3 10 2,1,6,5 < 1,6,5,4,3 11 2,6 <6,1<5<4<3 12 5,2,3,1,4,6 13 2,6< 6,1 < 5 <4 < 3 14 5,3<3,6<6,4< 1,2 15 3,1,5,6 ,2,4 16 5,3<6,4,1<2 17 5,3,6,4< 4 ,1 < 2 18 3,4,5,6 ,2,1 19 6,5,3,1,4<2
1 = Healthy Full Term Males 2 = Healthy Full Term Females 3 = Premature Males 4 = Premature Females 5 = High Risk Full Term Males 6 = High Risk Full Term Females 79
TABLE 12
SUMMARY OF ANALYSIS OF COVARIANCE ACROSS THE GROUPS FOR THE AUDITORY CARDIAC DATA
VAR. NO. D.F.F-RATIO F PROB.
4 5,473 2.81 .016 5 5,473 4.02 .001 6 5,473 11.99 .001 7 5,473 2.87 .015 8 5,473 5.23 .001 9 5,473 8.62 .001 10 5,473 1.16 NS 11 5,473 3.55 .004 12 5,473 .98 NS 13 5,473 1.52 NS 14 5,473 12.19 .001 15 5,473 1.20 NS 16 5,473 10.23 .001 17 5,473 1 1.19 .001 18 5,473 .87 NS 19 5,473 4.31 .001
NS = Not Significant 80
TABLE 13
HEALTHY FULL TERM MALES AVERAGE CARDIAC RESPONSE TACTILE MODALITY
VAR.NO MEAN S.D. MAX. MIN. RANGE
1 122.7 17.4 144.0 90.3 53.7 2 4.6 1.3 6.9 2.5 4.4 3 122.0 17.0 147.5 76.1 71.4 4 4.5 3.1 16.1 0.7 15.4 5 125.9 16.4 152.9 78.4 74.5 6 5.2 3.7 18.6 0.5 18.1 7 120.9 17.9 150.3 74.1 76.2 8 4.9 3.6 16.2 0.7 15.5 9 134.2 14.2 156.0 99.0 57.0 10 4.6 3.1 15.0 1.0 14.0 11 111.5 19.8 141.0 62.0 79.0 12 13.6 6.4 28.0 3.0 25.0 13 123.5 15.9 154.0 69.0 85.0 14 10.7 8.6 47.0 0.0 47.0 15 12.4 10.6 46.0 0.0 46.0 16 22.8 11.5 50.0 2.0 48.0 17 3.8 6.4 24.9 -15.7 40.6 18 5.0 7.5 32.9 -13.5 46.4 19 - 1.1 8.0 20.6 -26.7 47.3 81
TABLE 14
HEALTHY FULL TERM FEMALES AVERAGE CARDIAC RESPONSE . TACTILE MODALITY
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 115.6 10.8 129.8 93.2 36.6 2 4.9 2.4 9.0 1.6 7.4 3 113.9 10.9 143.2 89.6 53.6 4 3.9 2.4 12.5 1.0 11.5 5 117.9 9.1 142.6 102.4 40.2 6 5.3 3.3 17.6 0.8 16.8 7 113.5 13.3 146.7 87.7 59.0 8 4.8 2.8 16.6 1.0 15.6 9 125.9 9.7 153.0 107.0 46.0 10 5.4 3.3 15.0 1.0 14.0 11 102.1 12.5 134.0 70.0 64.0 12 14.2 6.1 27.0 5.0 22.0 13 113.9 11.5 144.0 84.0 60.0 14 12.0 8.8 37.0 0.0 37.0 15 13.0 9.1 39.0 1.0 38.0 16 25.0 11.7 55.0 5.0 50.0 17 4.0 6.2 16.3 -9.4 25.7 18 4.3 8.0 22.6 -19.1 41.7 19 0.0 8.5 26.8 -29.8 56.6 82
TABLE 15
PREMATURE MALES AVERAGE CARDIAC RESPONSE TACTILE MODALITY
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 145.8 14.7 163.2 116.9 46.3 2 3.5 1.1 5.6 1.4 4.2 3 141.0 15.7 167.3 103.7 63.6 4 2.3 1.3 7.5 0.4 7.1 5 142.0 16.0 170.8 99.5 71.3 6 2.5 1.3 6.5 0.5 6.0 7 141.4 16.8 168.9 101.1 67.8 8 2.3 1.5 6.9 0.3 6.6 9 148.0 15.7 173.0 110.0 63.0 10 7.0 4.2 15.0 1.0 14.0 11 132.4 16.9 166.0 85.0 81.0 12 16.2 6.2 29.0 3.0 26.0 13 140.5 16.0 170.0 102.0 68.0 14 7.3 5.2 22.0 0.0 22.0 15 8.7 8.4 58.0 0.0 58.0 16 16.0 8.9 67.0 5.0 62.0 17 1.0 4.5 11.1 -13.2 24.3 18 0.5 4.8 13.3 -13.7 27.0 19 0.4 6.1 18.4 - 11.6 30.0 83
TABLE 16
PREMATURE FEMALES AVERAGE CARDIAC RESPONSE TACTILE MODALITY
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 136.6 17.1 158.5 104.0 54.5 2 5.1 1.5 7.3 1.8 5.5 3 132.0 14.9 161. 1 102. 1 59.0 4 2.3 1.4 6.9 0.3 6.6 5 134.6 12.9 162.2 108.6 53.6 6 3.2 2.2 11.4 0.5 10.9 7 134.6 15.3 162.5 103.8 58.7 8 3.3 2.6 14.8 0.5 14.3 9 141.9 12.6 166.0 117.0 49.0 10 7.5 3.9 15.0 1.0 14.0 11 123.4 16.7 149.0 90.0 59.0 12 18.3 6.9 30.0 6.0 24.0 13 132.2 15.4 165.0 96.0 69.0 14 9.7 6.7 36.0 0.0 36.0 15 9.5 8.9 34.0 0.0 34.0 16 19. 1 9.2 40.0 3.0 37.0 17 2.5 5.0 22.9 -7.6 30.5 18 -0.0 5.7 16.6 - 11.6 28.2 19 2.6 7.0 25.2 -16.9 2.1 84
TABLE 17
HIGH RISK FULL TERM MALES AVERAGE CARDIAC RESPONSE TACTILE MODALITY
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 129.7 14.2 149.0 104.5 44.5 2 4.1 2.3 8.1 0.5 7.6 3 123.8 15.7 153.0 96.5 56.5 4 2.4' 1.8 8.6 0.3 8.3 5 125.7 15.5 152.0 98.6 53.4 6 3.5 2.3 11.2 0.5 10.7 7 122.9 16.3 154.7 88.1 66.6 8 3.4 2.5 13.4 0.4 13.0 9 132.3 16.9 161.0 103.0 58.0 10 6.1 4.1 15.0 1.0 14.0 11 113.6 14.6 144.0 84.0 60.0 12 14.7 6.3 29.0 5.0 24.0 13 124.0 16.0 153.0 96.0 57.0 14 8.1 5.6 22.0 0.0 22.0 15 10.3 8.2 32.0 0.0 32.0 16 18.4 9.2 44.0 4.0 40.0 17 1.9 4.1 14.3 -8.4 22.7 18 2.8 6.5 25.7 -9.8 35.5 19 -0.8 6.9 14.9 -24.9 39.8 85
TABLE 18
HIGH RISK FULL TERM FEMALES AVERAGE CARDIAC RESPONSE TACTILE MODALITY
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 118.7 7.9 128.7 105.3 23.4 2 4.1 1.6 6.8 1.3 5.5 3 116.7 14.7 145.5 88.4 57.1 4 3.2 2.6 15.2 0.5 14.7 5 118.6 13.1 147.4 95.8 51.6 6 3.9 2.6 11.8 0.8 11.0 7 118.7 14.3 149.9 91.8 58.1 8 3.4 2.3 10.5 0.3 10.2 9 126.3 12.0 151.0 103.0 48.0 10 7.0 3.7 15.0 1.0 14.0 11 108.8 17.0 146.0 82.0 64.0 12 19.0 5.9 29.0 6.0 23.0 13 115.8 15.1 145.0 87.0 58.0 14 10.5 7.7 43.0 0.0 43.0 15 7.3 7.5 40.0 0.0 40.0 16 17.9 10.0 44.0 4.0 40.0 17 1.9 5.6 18.0 -14.9 32.9 18 -0.0 5.0 13.3 -13.4 26.7 19 1.9 7.0 31.4 -19.3 50.7 86
TABLE 19
SUMMARY OF ONE-WAY ANOVAS ACROSS THE GROUPS FOR THE TACTILE CARDIAC DATA
VAR.NO. D.F. F-RATIO F PROB.
1 5,474 52.85 .0001 2 5,474 8.61 .0001 3 5,474 36.13 .0001 4 5,474 13.71 .0001 5 5,474 35.08 .0001 6 5,474 13.89 .0001 7 5,474 35.55 .0001 8 5,474 1 1.26 .0001 9 5,474 32.08 .0001 10 5,474 6.74 .0001 11 5,474 34.80 .0001 12 5,474 9.93 .0001 13 5,474 35.36 .0001 14 5,474 4.58 .001 15 5,474 4.76 .001 16 5,474 8.74 .0001 17 5,474 3.81 .003 18 5,474 10.18 .0001 19 5,474 3.36 .006
NS = Not Significant 87
TABLE 20
POST-HOC TESTS OF SIGNIFICANCE FOR ONE-WAY ANOVAS ACROSS THE GROUPS ON TACTILE CARDIAC DATA
VARIANCE NUMBER HOMOGENEOUS SUBSETS
1 2 ,6 < 6 ,1 < 5 < 4 < 3 2 3 < 6 , 5 , 1 < 1,2,4 3 2,6< 1,5<4,3 4 3,4,5< 6,3 < 2,1 5 2,6< 5,1 < 4 < 3 6 3,4<4,5,6< 1,2 7 2<6,1,5<4<3 8 3 < 4 , 5 , 6 < 2,1 9 2,6< 5,1< 4 <3 10 1,2<2,5<5,3,6<3,6,4 11 2 < 6 ,1, 5 < 4 < 3 12 1,2,5< 2,5,3< 4 ,6 13 2,6<1,5<4<3 14 3,5,4<5,4,6<4,6,1,2 15 6,3,4,5< 5,1,2 16 3 , 6 , 5 , 4 0 , 2 17 3,6,5,4< 4,1,2 18 6 ,4,3< 5,2< 2,1 19 1,5,2,3< 2,3,6<3,6,4
1 = Healthy Full Term Males 2 = Healthy Full Term Females 3 = Premature Males 4 = Premature Females 5 = High Risk Full Term Males 6 = High Risk Full Term Females 88
TABLE 21
SUMMARY OF ANALYSIS OF COVARIANCE ACROSS THE GROUPS FOR THE TACTILE CARDIAC DATA
VAR.NO. D.F. F-RATIO F PROB.
4 5,473 7.95 .001 5 5,473 4.68 .001 6 5,473 5.36 .001 7 5,473 3.60 .003 8 5,473 4.54 .001 9 5,473 7.37 .001 10 5,473 4.71 .001 11 5,473 2.77 .018 12 5,473 9.67 .001 13 5,473 1.43 NS 14 5,473 1.83 NS 15 5,473 4.23 .001 16 5,473 5.36 .001 17 5,473 2.13 .060 18 5,473 8.04 .001 19 5,473 3.38 .005
NS = Not Significant TABLE 22
CORRELATION MATRIX ACROSS ALL
60 INFANTS FOR AUDITORY CARDIAC DATA
VAR.NO. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
1 1.00 -.07 .90** -.21 .88** -.35** .85** -.18 .84** .09 .85** .01 .88** -.26* -.01 -.21 -.22 -.06 -. 11 2 1.00 -.07 .34** .03 .35** .01 .35** .12 .01 -.18 .07 -.06 .32* .28* .47** .30* .06 . 17 3 1.00 -.30* .94** -.42** .89** -.22 .88** .04 . 90** -.02 .97** -.37** .07 -.25 -.34** -.01 -.24 4 1.00 -.19 .54** -.20 .37** -.09 -.02 -.33** .05 -.30* .44** . 16 .47** .33** .06 .20 5 1.00 -.28* .94** -. 14 .95** -.01 .86** .01 .94** -.18 . 10 -.06 .01 .01 -.01 6 1.00 -.23 .39** -. 10 -.08 -.46** .07 -.48** .77** .05 .65** .45** -. 10 .40** 7 1.00 -.25** . 95** . 14 .86** . 13 .87** -.06'' -.03 -.07 -.01 -.34** .24 8 1.00 -.05 -. 10 -.39** -.17 -.20 .31* .42** .57** .25* .34** -.07 9 1.00 . 11 .81** .09 .87** .05 .09 . 1 1 .06 -. 15 . 15 10 1.00 • .15 .49** .01 .17 -.23 -.04 -.12 -.43** .22 11 1.00 .01 .88** -.32* -.30* -.48** -.27* -. 16 -.08 12 1.00 -.03 .23 -.06 . 15 .08 -.38** .33** 13 1.00 -.45** .17 -.23 -.25* .03 -.20 14 1.00 -. 18 .67** .53** -.31* .65** 15 1.00 .61** .08 .34** -.20 16 1.00 .54** .02 .37** 17 1.00 .06 .63** 18 1.00 -.69** 19 1.00
*P < .05 **P < .01
03 TABLE 23
CORRELATION MATRIX ACROSS ALL 60 INFANTS FOR TACTILE CARDIAC DATA
r \ . 1 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18
I .87** -.28* .87** -.35** .85** -.38** .86** .22 .82** . 14 .86** -.20 -.09 -.22 -. 16 -. 18 2 -.02 .23 .01 .30* -.03 .24 .08 -.01 -. 10 -.05 -.02 .23 .21 .33** .09 . 10 3 1.00 -.35** .95** -.44** .92** -.44** .91** .22 .89** .17 .96** -.33** -.02 -.25* .35** -.19 4 1.00 -.31* .57** -.35** .48** -.20 -. 12 -.40** -.09 -.33** .35** .28* .47** .20 .21 5 1.00 -.37** .93** -.38** .96** . 17 .83** . 16 .95** •-.20 -.01 -. 15 -.04 -. 1 1 6 1.00 -.39** .61** -.19 -.21 -.50** -. 14 -.44**, .65** .24 .65** .30* . 18 7 1.00 -.48** .92** .32* .91** .28* .90** -.15 -.17 -.25* -.13 -.46** 8 1.00 -.26* -. 19 -.58** -.23 -.40** .37** .45** .64** .26* .39** 9 1.00 .25* .83** .20 .91** -.01 .01 .00 -.03 -. 19 10 1.00 .30* .47** . 19 .07 -.22 -. 14 -.20 -.47** 11 1.00 .21 .86** -.26* -.41** -.54** -.21 -.35** 12 1.00 . 15 .05 -. 12 -.06 -.07 -.36** 13 1.00 -.43** .09 -.22 -.21 -. 13 14 1.00 -. 18 .53** .44** -.09 15 1.00 .73** .04 .44** 16 1.00 .34** .32* 17 1.00 .27* 18 1.00 19 91
TABLE 24
SUMMARY OF ONE-WAY ANOVAS OVER EIGHT TRIALS FOR THE AUDITORY CARDIAC DATA
VAR.NO.FTMFTFPMPFHRMHRF
3 NS NSNSNS NS NS 4 NS NSNSNS NS NS 5 NS NSNSNS NS NS 6 NS NSNSNS NSNS 7 NS NS NSNSNSNS 8 NS NSNS NS NS NS 9 NS NS NSNSNSNS 10 NS NSNS NS NS NS 11 NSNS NSNSNSNS 12 .09 .07 NSNS NSNS 13 NSNS NSNS NSNS 14 NS NSNSNS NSNS 15 NS NS NS NS NSNS 16 NS NS NS NS NSNS 17 NS NS NS NS NSNS 18 NS ' NS NS NS NS NS 19 NS NS NSNS NS NS
FTM = Healthy Full Term Males FTF = Healthy Full Term Females PM = Premature Males PF = Premature Females HRM = High Risk Full Term Males HRF = High Risk Full Term Females 92
TABLE 25
SUMMARY OF ONE-WAY ANOVAS OVER EIGHT TRIALS FOR THE TACTILE CARDIAC DATA
VAR.NO.FTM FTF PM PF HRM HRF
3 NS NSNSNS NS NS 4 NS NSNS NS NSNS 5 NS NS NSNS NSNS 6 NS NS NSNS NSNS 7 NS NS NSNS NSNS 8 NS NS NSNS NSNS 9 NSNSNSNS NSNS 10 NS NS NSNS NSNS 1 1 NSNSNSNS NSNS 12 NS NS NSNS NSNS 13 NSNSNSNS NSNS 14 NSNSNSNS NSNS 15 NSNSNSNS NSNS 16 NS NS NS NS NS NS 17 NS NS NS NS NSNS 18 NSNSNSNS NS NS 19 NS NSNSNS NSNS
FTM = Healthy Full Term Males FTF = Healthy Full Term Females PM = Premature Males PF = Premature Females HRM = High Risk Full Term Males HRF =s High Risk Full Term Females 93
TABLE 26
HEALTHY FULL TERM MALES AVERAGE PERFORMANCE NON-NUTRITIVE SUCKING
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 7.2 3.9 12.8 2.3 10.5 2 3.9 3.7 12.8 0.7 12.0 3 6.5 2.9 13.3 3.9 9.4 4 2.7 1.3 6.0 1.5 4.5 5 12.7 7.5 26.6 4.4 22.1 6 4.8 2.9 9.9 1.6 8.3 7 59.1 25.6 113.6 31.6 82.0 8 16.9 8.5 35.1 5.8 29.2 9 1.8 0.1 2.1 1.4 0.7 10 0.1 0.0 0.2 0.0 0.2 11 50.0 9.4 63.5 35.5 27.9 12 50.2 14.1 69.4 22.0 47.4 13 86.2 19.6 133.0 64.0 69.0 94
TABLE 27
HEALTHY FULL TERM FEMALES AVERAGE PERFORMANCE NON-NUTRITIVE SUCKING
^ ------VAR.NO MEAN S.D. MAX. MIN. RANGE
1 8.0 4.2 17.0 3.4 13.5 2 3.7 2.6 9.2 0.6 8.6 3 5.2 1.9 9.1 2.7 6.3 4 2.5 1.3 6.2 1.6 4.6 5 13.6 6.4 25.7 6.6 19. 1 6 6.2 4.4 15.3 0.7 14.6 7 65.8 22.9 106.1 32.7 73.4 8 18.8 4.0 26. 1 10.6 15.4 9 1.8 0.1 2.1 1.5 0.5 10 0 . 1 0.0 0.2 0.0 0.2 11 61.1 21.4 99.5 34.5 65.0 12 42.6 14.7 73.0 19.5 53.5 13 106.6 38. 1 173.0 60.0 113.0 95
TABLE 28
PREMATURE MALES AVERAGE PERFORMANCE NON-NUTRITIVE SUCKING
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 6.0 2.2 11.1 3.3 7.7 2 3.0 1.1 5.6 1.2 4.3 3 6.0 1.8 7.7 1.8 5.9 4 2.7 1.0 4.8 1.3 3.5 5 9.9 3.9 17.3 5.7 11.6 6 4.7 1.7 8.2 2.2 5.9 7 41.7 22.6 96.9 17.9 79.0 8 12.5 4.8 24.6 8.2 16.3 9 1.6 0.2 2.1 1.3 0.7 10 0.2 0.0 0.3 0.0 0.2 11 57.3 18.8 89.0 33.0 56.0 12 54.9 13.1 70.0 27.5 42.5 13 92.7 29.3 139.0 46.0 93.0 96
TABLE 29
PREMATURE FEMALES AVERAGE PERFORMANCE NON-NUTRITIVE SUCKING
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 5.4 2.0 8.6 2.7 5.9 2 3.1 2.6 9.5 0.9 8.6 3 4.7 1.6 7.0 2.0 4.9 4 2.2 1.1 4.5 0.7 3.8 5 8.2 3.3 14.0 3.6 10.4 6 4.2 3.2 11.5 1.6 9.8 7 48.2 18.3 87.0 23.2 63.8 8 13.5 4.1 18.9 6 .4 12.4 9 1.5 0.1 1.7 1.3 0.4 10 0.2 0.0 0.3 0.0 0.2 11 59.1 16.1 84.0 27.0 57.0 12 50.3 13.3 74.0 31.0 43.0 13 88.3 25.9 124.0 36.0 88.0 97
TABLE 30
HIGH RISK FULL TERM MALES AVERAGE PERFORMANCE NON-NUTRITIVE SUCKING
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 7.1 3.0 13.0 3.4 9.6 2 4.3 1.9 7.7 1.6 6.0 3 5.5 1.6 7.7 2.6 5.0 4 3.2 1.9 6.9 0.9 5.9 5 11.1 4.6 19.0 5.4 13.5 6 6.6 3.1 12.4 2.4 9.9 7 60.6 19.7 102.4 30.4 72.0 8 15.6 5.4 23.7 6.8 16.9 9 1.6 0.1 1.9 1.4 0.4 10 0.2 0.1 0.4 0.0 0.3 11 67.3 16.2 99.5 42.0 57.5 12 48.2 19.7 82.5 14.0 68.5 13 109.5 33.9 187.0 66.0 121.0 98
TABLE 31
HIGH RISK FULL TERM FEMALES AVERAGE PERFORMANCE NON-NUTRITIVE SUCKING
VAR.NO. MEAN S.D. MAX. MIN. RANGE
1 5.8 2.4 8.5 1.7 6.8 2 2.7 1.9 6.6 0.3 6.2 3 5.9 2.3 9.3 3.2 6 . 1 4 3.3 2.2 6.8 0.5 6.3 5 9.2 3.8 14.4 3.0 11.3 6 3.9 2.9 10.6 0.7 9.8 7 63.9 33.1 110.3 26.9 83.4 8 19.0 10.9 37.8 6.7 31.1 9 1.6 0 . 1 1.8 1.2 0.5 10 0.2 0.0 0.3 0.0 0.3 11 55.2 13.2 72.0 31.5 40.5 12 56.7 14.6 84.0 37.5 46.5 13 87.0 22.7 110.0 40.0 70.0 99
TABLE 32
SUMMARY OF ANALYSIS OF VARIANCE ACROSS THE GROUPS FOR THE NON-NUTRITIVE SUCKING DATA
VAR.NO.D.F. F-RATIO F PROB.
1 5,54 1.01 NS 2 5,54 .60 NS 3 5,54 .95 NS 4 5,54 .60 NS 5 5,54 1.60 NS 6 5,54 1.18 NS 7 5,54 1.55 NS 8 5,54 1.55 NS 9 5,54 2.96 .02 10 5,54 .47 NS 11 5,54 1.26 NS 12 5,54 1.10 NS 13 5,54 1.28 NS
NS = Not Significant TABLE 33
CORRELATION MATRIX ACROSS ALL 60 INFANTS FOR NON-NUTRITIVE SUCKING DATA
VAR.l 2 3 4 5 6 7 8 9 10 1 1 12
1 .73** .39** .33** .96** .72** .28* .21 .01 -.38** .44** -.40** 2 .00 .08 . 10 .71** .86** . 16 . 10 .01 -. 12 .48** -.56** 3 1.00 .77** .37** . 13 .21 .18 .04 -.08 -.30* .34** 4 1.00 .26* . 13 . 19 .25* -. 12 -.02 -.25* .19 5 1.00 .69** .27* . 19 .25* -.37** .40** -.38** 6 .00 . 16 .09 .00 -.21 .57** -.53** 7 1.00 .78** -.01 -.16 . 1 1 -.07 8 1.00 -.03 .05 -.09 -. 11 9 1.00 . 11 -.21 .05 10 1.00 -.42** . 11 11 1.00 -.42** 12 1.00 13
* p <
* * p < 101
TABLE 34
SUMMARY TABLE OF STEPWISE REGRESSION ANALYSIS FOR SUDITORY CARDIAC DATA
VAR.NO. TWO MOST SIGNIFICANT PREDICTORS
1 3,8 2 8,9 3 3,8 4 4,6 5 3,8 6 9,2 7 3,8 8 6,4 9 3,8 10 1,5 11 3,8 12 5,6 13 3,8 14 9,8 15 6,9 16 6,8 17 9,8 18 1,9 19 6,3 102
TABLE 35
SUMMARY TABLE OF STEPWISE REGRESSION ANALYSIS FOR TACTILE CARDIAC DATA
VAR.NO. TWO MOST SIGNIFICANT PREDICTORS
1 3,8 2 8,9 3 3,8 4 9,4 5 3,8 6 1,6 7 1,7 8 6,4 9 3,8 10 1,9 11 1,8 12 7,5 13 3,8 14 6,2 15 6,4 16 6,4 17 5,1 18 9,1 19 8,1 103
TABLE 36
SUMMARY TABLE OF STEPWISE REGRESSION ANALYSIS FOR THE NON-NUTRITIVE SUCKING DATA
VAR.NO. TWO MOST SIGNIFICANT PREDICTORS
1 5,1 2 7,5 3 8,2 4 9,5 5 5,1 6 7,5 7 2,4 8 7,2 9 9,4 10 5,4 11 9,5 12 6,1 13 4,5 TABLE 37
CORRELATION MATRIX ACROSS ALL 60 INFANTS RELATING A I) PTTORY CARDIAC DATA AND NON-NUTRITIVE SUCKING DATA
HR. VAR.NO. 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 18 19
1 -. 12 .22 -. 12 .05 -.06 . 15 -. 10 .13 -.08 -.13 -. 13 -.07 -. 10 .06 .06 . 10 . 18 . 12 .05 2 -.02 .09 -.03 .00 -.02 -.02 -.05 .02 -.05 -.07 -.02 .02 -.01 -.07 .03 -.03 .06 . 10 -.03 3 -. 13 .13 -.09 .02 -.06 . 10 -.05 .04 -.05 .00 -.09 -.02 -.08 .07 .00 .05 .09 -.02 .09 o 4 -. 1 1 .09 -.09 -.02 -.09 -.04 -.09 -.01 -.10 -.05 -.1 1 -.03 -.07 -.03 .06 .02 -.01 .00 .00 * 5 -. 12 .24 -. 14 . 11 -.07 .22 -. 1 I . 18 -.07 -. 14 -. 15 -.05 -. 12 . 12 .07 .16 .23 . 12 .08 css 6 -.07 . 14 -.05 .07 -.01 .06 -.03 .08 -.03 -.10 -.05 -.01 -.04 .01 .04 .04 . 14 .08 .05 > n 7 -.29* .0b -.38** . 1 1 -.33** .27* -.33** .17 -.29* -. 10 -.4 1** .05 -.38** .22 . 10 .26* .20 .08 .09 o 8 -.32* .06 -.36** . 14 -.31* .30* -.33** , 17 -.27* -. 10 -.38** .01 -.36** .23 .09 .25* .21 . 1 1 .07 g 9 -. 16 .04 -.13 .20 -.13 .33** -. 14 .23 -.07 -.09 -.20 .01 -.19 .25* .05 .24 . 19 .05 . 10 u 10 - . IS -.30* -. 14 -.08 -. 18 -.07 -. 15 -. 12 -. 19 .08 -.09 .02 -. 15 -.04 -. 12 -. 12 -.08 -.07 .00 w 1 1 .07 . 12 .03 .02 .06 -.06 .02 .02 ' .01 -.09 .02 • -.03 .05 -.09 .06 -.02 .05 .09 -.02 12 -.01 -.09 .02 -.08 -.02 -. 1 1 .02 -. 10 -.02 . 14 .03 .00 .01 -.06 -.07 -. 10 -. 11 . 14 .02 13 .03 . 17 -.02 . 14 .03 .08 -.01 . 1 1 .01 -. 14 -.04 -.03 -.01 .02 .08 .08 . 14 . 10 .03
*P < .05
**P < .01
O -P- TABLE 38
CORRELATION MATRIX ACROSS ALL 60 INFANTS RELATING TACTILE CARDIAC DATA AND NON-NUTRITIVE SUCKING DATA
HR. VAR.NO. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
1 -. 12 .22 -. 16 .04 -.13 . 16 -. 16 .08 -.12 -. 16 -. 13 -. 12 -.16 . . 13 -.02 .07 . 10 .10 -.02 2 -.02 .09 -.05 -.05 -.04 .02 -.05 -.06 -.06 -.10 .00 -. 11 -.04 -.02 -.08 -.08 .00 .02 -.02 . 3 -. 13 . 13 -. 12 .08 -.10 . 11 -.09 .04 -.08 -.09 -.09 .00 -. 14 • . 16 . -.07 .04 .09 -.01 .09 g 4 -. 11 .09 -.13 .02 -.09 . 11 -.08 .02 -.09 -.08 -. 10 .01 -. 13 . 13 -.05 .04 .14 .00 . 12 . 5 -. 12 .24 -. 16 .09 -.13 .21 -.17 . 12 -. 10 -.17 -. 14 -. 15 -. 15 . 15 .01 . 10 . 10 . 14 -.05 a t r < ° -.07 . 14 -.07 -.01 -.06 .08 -.07 .00 -.06 -. 10 -.04 -.13 -.07 .06 -.05 .00 .04 .05 -.02 > 7 -.30* .06 -.34** .17 -.33** .23 -.32* .17 -.30* -.09 -.31* -.03 -.34** .17 .00 . 11 . 10 .08 .02 g 8 -.32** .06 -.36** .21 -.35** .30* -.33** . 19 -.31* -. 11 -.36** -.01 -.35** . 16 .08 .18 .11 .06 .04 5 9 -. 15 .04 -.13 .24 -.12 .23 -. 17 .21 -.08 -. 11 -.15 -.13 -.11 . 12 . 11 .17 .08 . 19 -.12 g 10 -.18 -.30* -. 19 -.06 -.21 -.09 -. 15 -.06 -.24 - -.01 -. 15 .07 -.19 -.07 -.06 -.09 -.04 -. 11 .06 « 11 .07 . 12 .05 -.12 .03 -.09 .00 -.07 .01 -.02 .04 -.08 .03 -.04 -.02 -.05 -.06 .07 -. 11 12 -.01 -.09 .04 -.04 .02 -. 15 .04 -.08 .00 .06 .03 . 1 1 .03 -.07 -.01 -.06 -.05 -.07 .04 13 .03 .17 .01 -.02 .00 .02 -.05 .00 .00 -.06 -.01 -. 12 -.01 .03 .01 .03 -.03 . 13 -. 14
*P < .05
**P < .01
O Ln CHAPTER VI
DISCUSSION
This chapter deals with the major findings of the study and con siders them in relation to previously reported results. The finding of significant group differences on the measure of resting heart rate level, with premature infants having higher heart rates than both full term healthy and high risk infants, is supportive of the course of development delineated by Lewis (1970), Steinschneider (1971), and
Parmelee (1964). The reduced rates of full term and high risk female infants relative to their male counterparts suggest the operation of a sex factor. Group differences on the measure of resting heart rate variability, with full term infants having the highest variability and premature males the lowest, is consistent with the findings of
Stamps (1980, 1977), Vallbona (1965), Urbach (1965), and deHaan (1971), and reinforce the notion that variability is an indicator of mature, healthy cardiac control mechanisms.
The correlational analysis indicates a significant relationship between resting heart rate level, prestimulus magnitude, and various measures of the cardiac response as expected by the Law of Initial
Value (Wilder, 1967). The relationship between resting heart rate variability and measures of cardiac responsivity support the role of
106 107 variability as a determinant of responsiveness as espoused by Porges
(1973, 1974), Hon (1968), and Vranekovic, Hock, Isaac, and Cordero
(1974). Further, the lack of a relationship between the measures of heart rate level and variability suggests that these variables work as independent factors.
The finding of cardiac acceleration as the prevalent response for all groups in both the auditory and tactile modalities supports the findings summarized by Graham and Jackson (1970) as typical of the neonatal response to exteroceptive stimulation. The presence of a rebound deceleration is at variance with the results of several stud ies (Keen, Chase, and Graham, 1965; Graham et al., 1968), but sup ports the findings of Hock (1971), Steinschneider (1971), and Vall bona (1963). The factor determining the biphasic response is most likely found in the procedure employed. An intense 100 dB stimulus in the auditory modality and an annoying stimulus in the tactile modality are presented to a quietly sleeping infant, and the resultant large accelerations increase the likelihood of "homeostatic overcorrection" and therefore a rebound deceleration below prestimulus level.
The group differences noted on the various measures of the cardiac response in both modalities support the notions of Porges (1977),
Schulman (1969), Hon (1968), and Urbach (1965). The prevalent view is that various groups of newborn infants (full term, premature, high risk, etc.) respond in a similar manner to identical stimulation, acceleration with the presence or absence of rebound deceleration, but that the magnitude and temporal aspects of the response may differ depending on whether the subject is characterized by neorological 108 immaturity, cortical damage, or transient CNS depression (Stamps,
1980; Adkinson and Berg, 1976; Kittner and Lipsitt, 1976; Rose et al.,
1976).
The finding of group differences in sucking rate are in agreement with several previous studies. The decreased sucking rates found in the premature sample are consistent with those reported by Dubignon et al. (1969) and Gryboski (1969), and support the idea that sucking behavior is largely a maturationally-dependent reflex motor behavior, since premature rates remain low despite their increased extrauterine experience (in this sample 10 days of age vs. 2 or 3 for the full term group). The depressed sucking rates of the high risk group support the findings of Kron (1973), Wolff (1968), and Dreier and Wolff
(1972), and are consistent with the belief that slow and dysrhythmic sucking may reflect CNS depression and serve as a sensitive indicator of subclinical disturbances in neurological function in infants lack ing overt signs of pathology.
One factor which was evident from a consideration of the individ ual raw data was that of extreme variability within all of the groups, particularly on the measures of sucking behavior. In many cases it was possible to identify visually records that were deviant on several measures (see Figures 2, 3, and 4). However, the presence of "normal" records within the same group led to an apparent overlap of distribu tions and a lack of statistically significant separation. Thus, indi vidual records could be shown to be depressed when compared to as yet unavailable normative data on the various measures of healthy full term sucking behavior. 109
The regression analysis relating nine predictor variables to the measures of heart rate and sucking data suggest the presence of three major factors working as a determinant of both heart rate and sucking behavior within the constant state of quiet sleep. Measures of birth weight, gestational age at test, length and head circumference can be viewed as different manifestations of a maturity factor. The Apgar scores at one and five minutes and the group variable are reflecting neurological integrity. The third factor is that of the sex of the infant. The correlational analysis relating the heart rate and suck ing data indicated that sucking amplitude and its variability were inversely related to measures of heart rate level, thus revealing the maturity factor affecting high heart rates and low sucking amplitude and variability in the premature group and low heart rates and high sucking amplitude and variability typical of the full term group.
Further, heart rate variability was related directly to amplitude and rate of sucking, the healthy full term group having high heart rate variability and high amplitude and rate of sucking, the premature group low variability and low amplitude and rate of sucking. Finally, the high risk group, with reduced heart rate variability showed re duced sucking rates.
The presence of a sex factor is suggested by the group differences in the cardiac responsivity data. On measures of resting heart rate level, variability, amount of acceleration in the auditory modality and latency in the tactile modality, sex took precedence as a dividing factor over group affiliation in two of the three levels of the sub set heirarchy. The role of sex as a factor in neonatal and infant 110
behavior has been considered by Korner (1973) and Kagan (1971), with
differences between the sexes reported in tactile, gustatory and
visual responsiveness as well as in spontaneous discharge behaviors
such as startles, smiles, and rhythmical mouthing. Kagan (1971) has
summarized the possible role of central nervous system organization
in such sex difference results. He cites experimental evidence to
show that dominance of left over right cerebral hemisphere may be less
equivocal in the young female than in the male. He states further
that since anatomical and physiological systems mature earlier in the
girl than in the boy, it is possible that the normal dominance rela
tion of left over right becomes established earlier in girls than in
boys. Kagan concludes that while the data available do not prove that
there are sex differences in CNS organization, it is sufficiently
strong to suggest this possibility.
The lack of habituation found in this study in both modalities
can be explained within the theoretical framework of Lacey (1959) and
is consistent with the experimental evidence cited by Graham and Clif
ton (1966). A relatively intense and/or bothersome stimulus was pre
sented to a sleeping infant in a manner eliciting large accelerations
as a component of a defensive reflex in the organism's attempt at
stimulus rejection. The vast-majority of studies have shown that the
defensive reflex is relatively resistant to habituation, particularly
over a short series of trials, and these results support that view.
While aspects of the auditory and tactile heart rate data suggest
differential responsiveness to the two types of stimulation, no state ments or conclusions were made in this regard. Inherent in the design 111
was a lack of counterbalancing in which half of each group of infants
received the tactile trials before the auditory stimulation. Thus, a
discussion of differences in responsivity to the stimuli is invali
dated due to the possibility of a position artifact, or fatigue factor.
A portion of the significance of this study, which supports the view of significantly different cardiac responsivity and non-nutritive
sucking patterns in premature and high risk infants relative to healthy full term newborns, can be viewed in its relation to the body
of research on similar functions in childhood and adult populations.
Sroufe and Waters (1973) reported significant differences in heart rate deceleration and reaction times for a control group vs. boys re
ferred for "special learning disability." Furby (1974) cites experi mental evidence to suggest that IQ and MA differences in "normal" and
"retarded" children reflect differences in the speed of habituation of the orienting reflex and the ability to inhibit responding.
Powazek and Johnson (1973) report that for retarded vs. nonretarded children, significant differences were noted in the ability to orient and attach signal value to stimulus events. Siddle and Glenn (1974) also report reduced speed of habituation of the skin conductance re sponse component of the orienting reflex in retarded vs. nonretarded male adults. Porges and Humphrey (1977) cite increases in respira tory and heart rate variability during a substained visual search task for a group of retarded adolescents, while the nonretarded group displayed suppression of variability of both measures, which is the mature type of response. 112
All of the above studies reflect differences which parallel those found in neonatal and early infant research on premature, high risk, and neurologically-impaired infants. Functions such as the ability to respond differentially to varying stimulations and to inhibit respond ing to repeated stimulation are basic processes of intelligence, with rapid habituators considered capable of rapid internal representation of external events. These measures of early cognitive-perceptual a- bility, their stability over time, the effects of impaired neonatal abilities on development, and their value in predicting future status need to be considered through longitudinal research. SUCKING PRESSURE (mmHg) 200 200 200 200 100 100 100 100 O- 0 o- - 0 ------* EAT PEAUE B t SI anj IO iS ft W B PREMATURE: Y ALTH HE ELH PEAUE .Wt 13 gm 1730 Wgt. B. PREMATURE HEALTHY SAMPLE PRINTOUTS DEMONSTRATING CARDIOTACHOMETER DEMONSTRATING PRINTOUTS SAMPLE OML UL TERM FULL NORMAL ML FR DATE FOR SMALL AND SUCKING DATA FOR SELECTED INFANTS SELECTED FOR DATA SUCKING AND 10 20 (E (SECONDS) T(ME FIGURE 2 FIGURE 30 I w££S&Sm PA 10-10 APGAR PA 5-8 - 5 APGAR PA 9-9 - 9 APGAR 40 -AGE G 7 HOURS 72 AGE ! G 94 HOURS 4 9 AGE G 7 HOURS 74 AGE 50 HOURS. CO < Z J U O 3 CO
INSTANTANEOUSLY RECORDED HEART RATE SUCKING PRESSURE (m m H g) 200 200 0 0 2 0 0 2 100 100 100 100 0 0 0 0 ------METHADOTC WITHDRAWAL PHEN38AR8ITAL T* FULL TERM o ERSE FL TERM; FULL DEPRESSED OML UL TERM FULL NORMAL SAMPLE PRINTOUTS DEMONSTRATING CARDIOTACHOMETER DEMONSTRATING PRINTOUTS SAMPLE a m o j x i i i x i- U - i- L ix x i i x ix L i- - U i- x i i i x j o m a 10 AND SUCKING DATA FOR SELECTED INFANTS SELECTED FOR DATA SUCKING AND j i i . i - U i u . i- U J .i.t .i.t J U i- . u i U - i . i 20 TIME (SECONOS) TIME FIGURE 4 FIGURE u u i n Ml UUJ 1 JJ ili. U iU U lU iM U U . ______%SO PA 2-6jG 69 HOURS 9 6 jAGE 6 - 2 APGAR ...... APGAR 9-9 PA 9-9 - 9 APGAR PA 9-9AE I HOURS SI AGE 9 - 9 APGAR “ 40 1 — G 9 HOURS 93 AGE . G 5 HOURS 54 AGE 50 J U ID I- o I Li S I o | p iTi— Z Cj ID < CHAPTER VII
SUMMARY
This investigation into neonatal cardiac responsivity and non nutritive sucking patterns was directed at three major areas of con cern. First was an interest in any group effects differentiating in fants on the various measures of cardiac responsivity and its change over trials for two modes of stimulation. The second major concern was possible group effects differentiating infants on the various measures of non-nutritive sucking behavior. The third area was a con sideration of the relationship between cardiac responsivity and non nutritive sucking behavior and whether these would be related in a manner reflecting neurological involvement or immaturity.
In order to investigate these areas of interest, sixty subjects were employed: 10 healthy full term males, 10 healthy full term fe males, 10 premature males, 10 premature females, 10 high risk males, and 10 high risk females. Healthy full term infants met the criteria of vaginal birth with normal pregnancy and delivery, an Apgar score of 8 or above at one and five minutes with normal blood cord biochem istries, and normal clinical examination during the hospital stay.
The premature infants met the criteria of birth weight below 1750 grams and a gestational age of 36 weeks or less. The high risk infants
116 117 met at least one of the following criteria: infants depressed at birth with Apgar scores of 6 or below at one and five minutes, offspring of
diabetic mothers, and infants with blood group incompatibilities. All
cardiac procedures were run while the infant was in a state of quiet
sleep. Each infant received a series of 10 auditory stimulations (a
100 dB, 3000 cps warbled tone of 5 second duration) and 10 tactile
stimulations (a wire filament drawn lightly across the cheek for a 2
second duration). There was a 45 second interstimulus interval between all stimulations and a 3 minute rest period between the auditory and
tactile sets of trials. Following the completion of all 20 stimula tions, a three to five minute rest period was observed, after which the
infant was aroused, presented a pacifier, and allowed from 10-20 min utes of sucking time. Infant heart rate was continuously monitored throughout the entire procedure.
The data obtained were scored with respect to 19 cardiac response variables defining the various aspects of the heart rate response curve, and 13 response variables defining non-nutritive sucking behav iors. Analyses performed included: an analysis of group differences on the auditory and tactile cardiac data, a correlational analysis on both the auditory and tactile cardiac data, an analysis of cardiac re sponsivity changes over trials, an analysis of group differences and a correlational analysis on the non-nutritive sucking data, a stepwise regression analysis relating nine predictive factors to both cardiac and non-nutritive sucking data, and finally a correlational analysis relating the cardiac and non-nutritive sucking data. 118
The analysis of the heart rate data indicated that the neonate's
cardiac response to both the auditory and tactile stimuli was acceler-
atory, with a rebound deceleration occurring after the peak of the ac-
celeratory phase which dropped the heart rate below the prestimulus
level. In the auditory modality, significant group effects were ob
tained for 15 of the 19 heart rate variables. Premature infants showed higher heart rate levels and lower variability scores. High risk in
fants showed heart rate levels comparable to the full term group, but were also decreased in the variability measures. The amount of accel eration was greatest for both healthy full term groups, with premature and high risk females grouping together in the middle range, and pre mature and high risk males grouping at the lowest accelerations. No
significant group differences were noted on the degree of rebound de celeration or on either variable defining the temporal aspects of the response. The above noted group effects other than prestimulus magni tude were retained following an analysis of covariance correcting for prestimulus level. In the tactile modality, significant group effects were obtained for all 19 heart rate variables. The nature and direc tion of the differences was essentially the same as noted for the audi tory data. In addition, the tactile latency scores showed a signifi cant group effect, with the full term infants responding quicker than the premature and high risk males who were grouped in the middle range, with the premature and high risk females the slowest responders. The analysis of covariance correcting for prestimulus level removed the group effect for the amount of accelerations as well as prestimulus magnitude. 119
Correlational analyses on the auditory and tactile data indicat ed significant relationships between all measures of heart rate level and between all measures of heart rate variability. The level and variability scores, however, were not related, suggesting that they acted as independent factors. The amount of acceleration was related to prestimulus magnitude but also to heart rate variability. Cardiac range was unrelated to heart rate level, but was related to all meas ures of variability. Both latency scores defining the temporal as pects of the response were significantly related. The analysis of responsivity change over trials indicated that for all groups there was no evidence of any response decrement in either modality. All trials in each modality for all groups were statistically identical.
The only variable of non-nutritive sucking behavior which showed a significant group effect was rate of sucking. Post-hoc tests of sig nificance indicated that both groups of premature and high risk in fants were reduced in their rate of sucking relative to the healthy full term infants. Correlational analysis indicated longer bursts of sucking were followed by longer rest periods. A significant correl ation was found relating longer bursts with greated amplitude of sucking, and number of sucks per burst with both rate and pressure of sucking. The results of the stepwise regression analysis on the auditory cardiac data indicated that for all measures of heart rate level, the most significant predictive factors were length and sex of the infant. For the measures of heart rate variability, the predic tors were head circumference, 5 minute Apgar score, group affiliation, and birth weight. For the latency scores, the significant predictors 120
were gestational age at test and 1 and 5 minute Apgar. For the meas
ures of acceleration, rebound deceleration, and cardiac range, the
predictors were 5 minute Apgar, sex, and group affiliation. Similar
results were obtained for the tactile cardiac data. The stepwise re
gression analysis on the non-nutritive sucking data indicated the fol
lowing significant predictive factors: for burst time and number of
sucks per burst, gestational age at test and 1 minute Apgar; for rest
time, sex and birth weight; for amplitude of sucking, birth weight and
head circumference; for rate of sucking, group affiliation and head
circumference; for total time sucking, group affiliation and 1 minute
Apgar; for total time resting, 5 minute Apgar and gestational age at
test; and for total number of sucks, head circumference and 1 minute
Apgar. The correlational analysis relating the cardiac data with the
measures of non-nutritive sucking behavior yielded similar results for
both the auditory and tactile modality. All measures of heart rate
level were significantly inversely related to sucking amplitude and
its variability. Cardiac range was positively related to the ampli
tude of sucking and its variability. Stimulus heart rate variability was positively related to amplitude of sucking, amplitude variability,
and rate of sucking. Resting heart rate was inversely related to variability in the rate of sucking.
The cardiac data were discussed relative to prior studies con
cerned with the determinants of the heart rate response to stimulation, with consideration given to the prevalent theories of the response and
its habituation. The meaning of the significant sex, maturity, and group affiliation factors was also considered, and convergence between the cardiac and sucking data was suggested. BIBILIOGRAPHY
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