DOCSLIB.ORG

Neurocase Abnormal Visual Phenomena in Posterior Cortical Atrophy

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Neurocase Abnormal Visual Phenomena in Posterior Cortical Atrophy This article was downloaded by: [Institute of Neurology] On: 9 September 2010 Access details: Access Details: [subscription number 917397660] Publisher Psychology Press Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37- 41 Mortimer Street, London W1T 3JH, UK Neurocase Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713658146 Abnormal visual phenomena in posterior cortical atrophy Sebastian J. Crutcha; Manja Lehmanna; Nikos Gorgoraptisb; Diego Kaskic; Natalie Ryana; Masud Husainb; Elizabeth K. Warringtona a Dementia Research Centre, Department of Neurodegeneration, UCL Institute of Neurology, University College London, UK b University College London, Institute of Cognitive Neuroscience, UK c Department of Neuro-otology, Charing Cross Hospital, London, UK First published on: 02 September 2010 To cite this Article Crutch, Sebastian J. , Lehmann, Manja , Gorgoraptis, Nikos , Kaski, Diego , Ryan, Natalie , Husain, Masud and Warrington, Elizabeth K.(2010) 'Abnormal visual phenomena in posterior cortical atrophy', Neurocase,, First published on: 02 September 2010 (iFirst) To link to this Article: DOI: 10.1080/13554794.2010.504729 URL: http://dx.doi.org/10.1080/13554794.2010.504729 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. NEUROCASE 2010, iFirst, 1–18 NNCS Abnormal visual phenomena in posterior cortical atrophy Abnormal Visual Phenomena in PCA Sebastian J. Crutch,1 Manja Lehmann,1 Nikos Gorgoraptis,2 Diego Kaski,3 Natalie Ryan,1 Masud Husain,2 and Elizabeth K. Warrington1 1Dementia Research Centre, Department of Neurodegeneration, UCL Institute of Neurology, University College London, UK 2Institute of Cognitive Neuroscience, University College London, UK 3Department of Neuro-otology, Charing Cross Hospital, London, UK Individuals with posterior cortical atrophy (PCA) report a host of unusual and poorly explained visual distur- bances. This preliminary report describes a single patient (CRO), and documents and investigates abnormally prolonged colour afterimages (concurrent and prolonged perception of colours complimentary to the colour of an observed stimulus), perceived motion of static stimuli, and better reading of small than large letters. We also evaluate CRO’s visual and vestibular functions in an effort to understand the origin of her experience of room tilt illusion, a disturbing phenomenon not previously observed in individuals with cortical degenerative disease. These visual symptoms are set in the context of a 4-year longitudinal neuropsychological and neuroimaging investigation of CRO’s visual and other cognitive skills. We hypothesise that prolonged colour after-images are attributable to relative sparing of V1 inhibitory interneurons; perceived motion of static stimuli reflects weak magnocellular function; better reading of small than large letters indicates a reduced effective field of vision; and room tilt illusion effects are caused by disordered integration of visual and vestibular information. This study contributes to the growing charac- terisation of PCA whose atypical early visual symptoms are often heterogeneous and frequently under-recognised. Keywords: Posterior cortical atrophy (PCA); Alzheimer’s disease (AD); Reversal of vision metamorphopsia; Gaze instability; Colour perception. INTRODUCTION Rogelet, Delafosse, & Destee, 1996; Ross et al., 1996) and indeed the condition is often referred to Downloaded By: [Institute of Neurology] At: 10:46 9 September 2010 Posterior cortical atrophy (PCA) is a progressive as the ‘biparietal’ or ‘visual’ variant of AD, or neurodegenerative condition involving prominent alternatively as Benson’s syndrome after the ori- tissue loss in the occipital, parietal and posterior ginal clinical description (Benson et al., 1988). The temporal cortex. PCA is characterised by the pro- distinction between PCA and the typical amnestic gressive deterioration of higher visual processing presentation of AD reflects the distribution of the and other posterior cortical functions, with first AD pathology. Individuals with PCA tend to have symptoms often occurring before the age of 65 a much greater density of senile plaques and neu- (e.g., Benson, Davis, & Snyder, 1988; Cogan, 1985; rofibrillary tangles in occipital cortex and regions De Renzi, 1986; Galton, Patterson, Xuereb, & of posterior parietal cortex and temporo-occipital Hodges, 2000). Alzheimer’s disease (AD) is the junction than those with typical AD, whilst showing most common underlying pathology (Cogan, 1985; fewer pathological changes in more anterior areas Address correspondence to Dr Sebastian J. Crutch, Dementia Research Centre, Box 16, National Hospital for Neurology and Neurosur- gery, Queen Square, London WC1N 3BG, UK. (E-mail: [email protected]). © 2010 Psychology Press, an imprint of the Taylor & Francis Group, an Informa business http://www.psypress.com/neurocase DOI: 10.1080/13554794.2010.504729 2 CRUTCH ET AL. (e.g., prefrontal cortex; Hof, Vogt, Bouras, & which are poorly recognised but nonetheless may Morrison, 1997; Tang-Wai et al., 2004). These and prove to be characteristic of PCA. This preliminary other differences between PCA and typical AD report replicates evidence of prolonged colour may be underpinned partially by genetic risk factors afterimages and better reading of small than large in the ApoE ε4 allele, which is strongly associated letters, and describes two further abnormal visual with typical AD but which does not seem to be a phenomena, namely perceived motion of static risk factor in PCA (Schott et al., 2006; Snowden stimuli and room tilt illusion effects. We argue that et al., 2007). these cognitive phenomena should be targets for In accordance with the distribution of pathology systematic evaluation in future cohort studies of and atrophy, patients with PCA tend to show rela- PCA, and have significant implications for tive sparing of many aspects of cognition such as patients’ functional abilities. memory and language and often have full insight into their condition. Thus in the early stages of the disease, they do not meet the standard diagnostic CLINICAL DESCRIPTION criteria for typical AD. Instead, the most promi- nent symptoms tend to include early visual pro- CRO is a right-handed retired health professional cessing deficits (e.g., achromatopsia, figure-ground who was referred to the National Hospital in 2004 discrimination problems), apperceptive agnosia, (aged 57 years old) with a 4-year history of progres- prosopagnosia, spatial deficits (e.g., visual disori- sive visual impairment. Early visual symptoms entation, spatial agnosia) and other symptoms included difficulty in making depth and distance such as optic ataxia, gaze apraxia and limb apraxia judgements, and the appearance of coloured patches (Benson et al., 1988; Freedman et al., 1991; Levine, at the edge of her visual field. Investigations con- Lee, & Fisher, 1993; McMonagle, Deering, Berliner, ducted prior to referral included a brain MRI which & Kertesz, 2006; Mendez, Ghajarania, & Perryman, was reported as normal, and an EEG showing poorly 2002; Rogelet et al., 1996; Ross et al., 1996). sustained alpha rhythm with temporal lobe slowing. Patients with PCA also experience other related Normal electroretinography (ERG) and visual and unrelated behavioural symptoms including evoked potentials (VEPs) investigations suggested dyslexia, acalculia, dysgraphia and visual inatten- normal retinal and optic nerve functions. Initial neu- tion (see Caine, 2004 for a review). ropsychological assessment also corroborated the However, in addition to these well-recognised clinical impression of predominant posterior cortical neuropsychological deficits, patients with PCA damage, with particular weaknesses on tests of visuo- also report a host of other symptoms, the anatomical spatial and visuoperceptual functions especially for and cognitive basis of which are much more poorly complex stimuli. Visual inspection of a brain MRI understood. For example, the tendency for indicated subtle biparietal atrophy but no hippocam- patients with progressive visual disturbance (who pal volume loss or vascular disease. There was no Downloaded By: [Institute of Neurology] At: 10:46 9 September 2010 might now be considered to have PCA) to have evidence of brainstem or cerebellar infarction on this greater difficulty recognising large as compared or subsequent MRI scans, which included diffusion with small pictures and other stimuli has been weighted imaging sequences. described (e.g., Pick, 1908 cited in Bender and Consequently, CRO was given a diagnosis of Feldman, 1972; Coslett, Stark,
Load more

Recommended publications
  • Pupil Responses Associated with Coloured Afterimages Are Mediated by the Magno-Cellular Pathway
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Aston Publications Explorer Vision Research 43 (2003) 1423–1432 www.elsevier.com/locate/visres Pupil responses associated with coloured afterimages are mediated by the magno-cellular pathway S. Tsujimura *, J.S. Wolffsohn, B. Gilmartin Neurosciences Research Institute, Aston University, Aston Triangle, Birmingham B4 7ET, UK Received 14 August 2002; received in revised form 27 January 2003 Abstract Sustained fixation of a bright coloured stimulus will, on extinction of the stimulus and continued steady fixation, induce an afterimage whose colour is complementary to that of the initial stimulus; an effect thought to be caused by fatigue of cones and/or of cone-opponent processes to different colours. However, to date, very little is known about the specific pathway that causes the coloured afterimage. Using isoluminant coloured stimuli recent studies have shown that pupil constriction is induced by onset and offset of the stimulus, the latter being attributed specifically to the subsequent emergence of the coloured afterimage. The aim of the study was to investigate how the offset pupillary constriction is generated in terms of input signals from discrete functional elements of the magno- and/or parvo-cellular pathways, which are known principally to convey, respectively, luminance and colour signals. Changes in pupil size were monitored continuously by digital analysis of an infra-red image of the pupil while observers viewed isoluminant green pulsed, ramped or luminance masked stimuli presented on a computer monitor. It was found that the amplitude of the offset pupillary constriction decreases when a pulsed stimulus is replaced by a temporally ramped stimulus and is eliminated by a luminance mask.
    [Show full text]
  • Real Time Measurement and Processing of Pupillary Light Reflex for Early Detection of Disease
    Journal of Computers Real Time Measurement and Processing of Pupillary Light Reflex for Early Detection of Disease Ippei Torii*, Takahito Niwa Aichi Institute of Technology, Dept. of Information Science, 1247 Yachigusa, Yakusa-cho, Toyota, Aichi, Japan. * Corresponding author. Tel.: 81-565-48-8121; email: mac[aitech.ac.jp Manuscript submitted January 10, 2019; accepted March 8, 2019. doi: 10.17706/jcp.14.3.161-169 Abstract: Recently, pupillary measurements have begun to be considered effective in the diagnosis of various physical conditions. Apart from optic neuropathy and retinal disorders, which are ocular diseases, diversions can be expected in the diagnosis of autonomic disturbance due to sympathetic and parasympathetic nerve disorders, cranial nerve disorders, cerebral infarction, depression, and diabetes. In this study, we have developed a real-time pupil diameter measuring system that is inexpensive and does not require a complicated device. When strong light is projected onto the eyeball, this system can measure the reaction time until the start of miosis, the time to achieve maximal miosis, and the difference in reaction speed of the left and right eyes. With this system, the status of a disease can be judged based on the distance from the threshold value. Key words: Real time measurement, eye movement, early detection of disease, image processing. 1. Introduction There are approximately one hundred million photoreceptor cells in the retina of human eyes. Light that shines on those cells is converted to nerve signals, which transmit the information to the brain, resulting in the visual recognition of objects. When light is radiated onto the eye, the pupillary light reflex is triggered, causing the pupillary diameter to decrease with a time delay of less than 1 sec.
    [Show full text]
  • Subliminal Afterimages Via Ocular Delayed Luminescence: Transsaccade Stability of the Visual Perception and Color Illusion
    ACTIVITAS NERVOSA SUPERIOR Activitas Nervosa Superior 2012, 54, No. 1-2 REVIEW ARTICLE SUBLIMINAL AFTERIMAGES VIA OCULAR DELAYED LUMINESCENCE: TRANSSACCADE STABILITY OF THE VISUAL PERCEPTION AND COLOR ILLUSION István Bókkon1,2 & Ram L.P. Vimal2 1Doctoral School of Pharmaceutical and Pharmacological Sciences, Semmelweis University, Budapest, Hungary 2Vision Research Institute, Lowell, MA, USA Abstract Here, we suggest the existence and possible roles of evanescent nonconscious afterimages in visual saccades and color illusions during normal vision. These suggested functions of subliminal afterimages are based on our previous papers (i) (Bókkon, Vimal et al. 2011, J. Photochem. Photobiol. B) related to visible light induced ocular delayed bioluminescence as a possible origin of negative afterimage and (ii) Wang, Bókkon et al. (Brain Res. 2011)’s experiments that proved the existence of spontaneous and visible light induced delayed ultraweak photon emission from in vitro freshly isolated rat’s whole eye, lens, vitreous humor and retina. We also argue about the existence of rich detailed, subliminal visual short-term memory across saccades in early retinotopic areas. We conclude that if we want to understand the complex visual processes, mere electrical processes are hardly enough for explanations; for that we have to consider the natural photobiophysical processes as elaborated in this article. Key words: Saccades Nonconscious afterimages Ocular delayed bioluminescence Color illusion 1. INTRODUCTION Previously, we presented a common photobiophysical basis for various visual related phenomena such as discrete retinal noise, retinal phosphenes, as well as negative afterimages. These new concepts have been supported by experiments (Wang, Bókkon et al., 2011). They performed the first experimental proof of spontaneous ultraweak biophoton emission and visible light induced delayed ultraweak photon emission from in vitro freshly isolated rat’s whole eye, lens, vitreous humor, and retina.
    [Show full text]
  • The Effect of Eye Movements and Blinks on Afterimage Appearance and Duration
    Journal of Vision (2015) 15(3):20, 1–15 http://www.journalofvision.org/content/15/3/20 1 The effect of eye movements and blinks on afterimage appearance and duration School of Psychology, Cardiff University, # Georgina Powell Cardiff, Wales, UK $ School of Psychology, Cardiff University, # Petroc Sumner Cardiff, Wales, UK $ Lyon Neuroscience Research Center, # Aline Bompas Centre Hospitalier Vinatier, Bron, Cedex, France $ The question of whether eye movements influence argued that afterimage signals are inherently ambigu- afterimage perception has been asked since the 18th ous, and this could explain why their visibility is century, and yet there is surprisingly little consensus on influenced by cues, such as surrounding luminance how robust these effects are and why they occur. The edges, more than are real stimuli (Powell, Bompas, & number of historical theories aiming to explain the Sumner, 2012). Helmholtz (1962) identified another cue effects are more numerous than clear experimental that is important to take into account when conducting demonstrations of such effects. We provide a clearer afterimage experiments: characterization of when eye movements and blinks do or do not affect afterimages with the aim to distinguish For obtaining really beautiful positive after- between historical theories and integrate them with a images, the following additional rules should be modern understanding of perception. We found neither saccades nor pursuit reduced strong afterimage observed. Both before and after they are devel- duration, and blinks actually increased afterimage oped, any movement of the eye or any sudden duration when tested in the light. However, for weak movement of the body must be carefully avoided, afterimages, we found saccades reduced duration, and because under such circumstances they invariably blinks and pursuit eye movements did not.
    [Show full text]
  • 2020 Lahiri Et Al Hallucinatory Palinopsia and Paroxysmal Oscillopsia
    cortex 124 (2020) 188e192 Available online at www.sciencedirect.com ScienceDirect Journal homepage: www.elsevier.com/locate/cortex Hallucinatory palinopsia and paroxysmal oscillopsia as initial manifestations of sporadic Creutzfeldt-Jakob disease: A case study Durjoy Lahiri a, Souvik Dubey a, Biman K. Ray a and Alfredo Ardila b,c,* a Bangur Institute of Neurosciences, IPGMER and SSKM Hospital, Kolkata, India b Sechenov University, Moscow, Russia c Albizu University, Miami, FL, USA article info abstract Article history: Background: Heidenhain variant of Cruetzfeldt Jacob Disease is a rare phenotype of the Received 4 August 2019 disease. Early and isolated visual symptoms characterize this particular variant of CJD. Reviewed 7 October 2019 Other typical symptoms pertaining to muti-axial neurological involvement usually appear Revised 9 October 2019 in following weeks to months. Commonly reported visual difficulties in Heidenhain variant Accepted 14 November 2019 are visual dimness, restricted field of vision, agnosias and spatial difficulties. We report Action editor Peter Garrard here a case of Heidenhain variant that presented with very unusual symptoms of pal- Published online 13 December 2019 inopsia and oscillopsia. Case presentation: A 62-year-old male patient presented with symptoms of prolonged af- Keywords: terimages following removal of visual stimulus. It was later on accompanied by intermit- Creutzfeldt Jacob disease tent sense of unstable visual scene. He underwent surgery in suspicion of cataratcogenous Heidenhain variant vision loss but with no improvement in symptoms. Additionally he developed symptoms of Oscillopsia cerebellar ataxia, cognitive decline and multifocal myoclonus in subsequent weeks. On the Palinopsia basis of suggestive MRI findings in brain, typical EEG changes and a positive result of 14-3-3 protein in CSF, he was eventually diagnosed as sCJD.
    [Show full text]
  • Pseudogaze in Afterimages
    Journal of Vision (2016) 16(5):6, 1–10 1 Where are you looking? Pseudogaze in afterimages Caltech Brain Imaging Center, Division of Humanities and Social Sciences, California Institute of Technology, # Daw-An Wu Pasadena, CA, USA $ Department of Psychological and Brain Sciences, Dartmouth College, Hanover, NH, USA Laboratoire Psychologie de la Perception, Universite´ # Patrick Cavanagh Paris Descartes, Paris, France $ How do we know where we are looking? A frequent gaze seems exceptionally well defined and we seldom assumption is that the subjective experience of our feel that we don’t know where we are looking within a direction of gaze is assigned to the location in the world visual scene. The conceptual equivalence of mental and that falls on our fovea. However, we find that observers physical gaze is ingrained to the point that the two can shift their subjective direction of gaze among concepts share almost all their terminology, even in different nonfoveal points in an afterimage. Observers scientific and technical usage. Terms such as ‘‘gaze,’’ were asked to look directly at different corners of a ‘‘look at,’’ ‘‘fixate,’’ etc. do not distinguish between the diamond-shaped afterimage. When the requested corner subjective sense of visual targeting and the physical was 3.58 in the periphery, the observer often reported pointing of the eyes at something. that the image moved away in the direction of the Whereas a large body of work exists regarding the attempted gaze shift. However, when the corner was at perceived direction of visual targets in egocentric space 1.758 eccentricity, most reported successfully fixating at the point.
    [Show full text]
  • The Moon Illusion Explained Introduction and Summary
    The Moon Illusion Explained Finally! Why the Moon Looks Big at the Horizon and Smaller When Higher Up. Don McCready Professor Emeritus, Psychology Department University of Wisconsin-Whitewater Whitewater, WI 53190 Email to: mccreadd at uww.edu Introduction and Summary [Revised 12/07/02] For many centuries, scientists have been puzzled by the illusion that the full moon at the horizon usually looks larger than it does later, at higher elevations toward the zenith of the sky. Many explanations (theories) have been offered. But, it is fair to say that the two dozen (or so) scientists most familiar with current research on the illusion have not yet accepted any one theory. The jury is still out. The theory reviewed in this article is relatively quite new (McCready, 1983, 1985, 1986). It begins with the basic assumption that, when most people say "the moon looks larger," they are referring primarily to the moon's angular subtense (McCready, 1965). That is, the horizon moon looks a larger angular size than the zenith moon. That experience is imitated if you look at the circles in the figure at the right, because the lower circle subtends a larger angle at your eye than the upper circle does. Angular Size Illusion. For the moon, that appearance is known as the moon illusion, because the angle the moon's diameter subtends at your eye measures about 1⁄2 degree of arc no matter where the moon is in the sky. That is, there is no physical (optical) reason why the horizon moon should look larger than the zenith moon: For instance, it has been known for centuries that the horizon moon is not "magnified' by the earth's atmosphere.
    [Show full text]
  • Sensation and Perception
    Sensation and Perception OUTLINE OF RESOURCES Introducing Sensation and Perception Podcast/Lecture/Discussion Topic: Person Perception (p. 3) UPDATED Basic Principles of Sensation and Perception Lecture/Discussion Topics: Sensation Versus Perception (p. 4) Top-Down Processing (p. 5) “Thin-Slicing” (p. 6) Classroom Exercises: A Scale to Assess Sensory-Processing Sensitivity (p. 6) UPDATED Human Senses Demonstration Kits (p. 6) UPDATED Classroom Exercises/Student Projects: The Wundt-Jastrow Illusion (p. 4) LaunchPad Video: The Man Who Cannot Recognize Faces* Thresholds Lecture/Discussion Topics: Gustav Fechner and Psychophysics (p. 7) Subliminal Smells (p. 8) Subliminal Persuasion (p. 9) Applying Weber’s Law (p. 10) Student Projects: The Variability of the Absolute Threshold (p. 8) Understanding Weber’s Law (p. 9) Sensory Adaptation Student Project: Sensory Adaptation (p. 10) UPDATED Classroom Exercises: Eye Movements (p. 10) Sensory Adaptation in the Marketplace (p. 11) Perceptual Set Lecture/Discussion Topic: Do Red Objects Feel Warmer or Colder Than Blue Objects? (p. 11) NEW Classroom Exercises: Perceptual Set (p. 11) UPDATED Perceptual Set and Gender Stereotypes (p. 12) Context Effects (see also Brightness Contrast, p. 22) Lecture/Discussion Topic: Context and Perception (p. 13) Vision: Sensory and Perceptual Processing Classroom Exercise/Student Project: Physiology of the Eye—A CD-ROM for Teaching Sensation and Perception (p. 13) LaunchPad Video: Vision: How We See* The Eye and the Stimulus Input Lecture/Discussion Topic:Classroom as Eyeball (p. 13) Student Projects: Color the Eyeball (p. 13) NEW Locating the Retinal Blood Vessels (p. 13) Student Projects/Classroom Exercises: Rods, Cones, and Color Vision (p. 14) UPDATED Locating the Blind Spot (p.
    [Show full text]
  • Sensory Physiology
    1 Human Physiology Lab (Biol 236L) Sensory Physiology External sensory information is processed by several types of sensory receptors in the body. These receptors respond to external stimuli, and that information is changed into an electrical signal (action potential) that is transmitted along the sensory division (afferent pathway) of the peripheral nervous system (PNS) to the central nervous system (CNS). This sensory signal initially occurs by activation of a sensory receptor. Receptor activation stimulates the opening or closing of ion-gated channels, which generates an action potential. The CNS, or integrating center, processes the information and then sends a response via motor division (efferent pathway) to effectors (muscle cells or glands) of the PNS for either a movement or secretory response, respectively. The sensory (afferent) division of the nervous system includes: 1) Somatic sensory division = transmission of sensory information from skin, fascia, joints, and skeletal muscles for balance and muscle movement to the CNS for interpretation. CNS will issue motor commands as needed to modify movements based on stimuli. The somatic sensory division can be involved in receiving sensory information that regulated involuntary and voluntary movement. In the skin there are several types of somatosensory receptors: mechanoreceptors, thermoreceptors, and nocireceptors. Mechanoreceptors are found in the skin, tongue, joints, and the bladder. They they detect pressure, vibration, and stretch. Thermoreceptors are found in the skin and hypothalamus; they can be divided into warm and cold receptors. Nocireceptors are found in the skin, cornea, visceral, joints, and skeletal muscles, and they are pain receptors that can be activated by mechanical, chemical, and even temperature extremes.
    [Show full text]
  • The Role of Accommodation in the Control of Binocular Rivalry (BR) Has Been the Basis of BR Control Because Granted Various Degrees of Importance by Es in the Past
    Therefore, he concluded that in the The role of accommodation in the case of direct stimulation of the two eyes with rivalry patterns, BR control control of binocular rivalry is effected through accommodation by the blurring of retinal images. However, Fry (1936) has not in fact shown that accommodation changes LEONC. LACK do take place during BR control with Flinders University of South Australia, Bedford Park, South Australia 5042 the eyes in the normal unparalyzed state. He infers that accommodation is The role of accommodation in the control of binocular rivalry (BR) has been the basis of BR control because granted various degrees of importance by Es in the past. The most recent control is lost when his S's eyes are investigation by Fry (1936) concluded that accommodation provides the basis of paralyzed. However, neither BR control through the blurring of retinal images. However, the present study McDougall (1903) nor George (1936) found that the introduction of very small artificial pupils (0.5 mm) did not found BR control to be obliterated by reduce BR control. It was concluded that if accommodation changes are paralyzing the intrinsic eye muscles. occurring with large pupils, the resulting image blurring plays no part in control Indeed, McDougall found hardly any of rivalry. Experiment 2 tested the effect of paralyzed intrinsic eye muscles and effect and warned (1906) against the found almost the same degree of control as in the normal state. The slight overemphasis of peripheral motor decrease of control that was present was attributed to a general performance systems in the control of attention.
    [Show full text]
  • Interaction Between Contours and Eye Movements in the Perception of Afterimages
    Journal of Vision (2016) 16(7):16, 1–11 1 Interaction between contours and eye movements in the perception of afterimages: A test of the signal ambiguity theory School of Psychology, Cardiff University, # Georgie Powell Cardiff, Wales, UK $ School of Psychology, Cardiff University, # Petroc Sumner Cardiff, Wales, UK $ School of Psychology, Cardiff University, James J. Harrison Cardiff, Wales, UK $ School of Psychology, Cardiff University, # Aline Bompas Cardiff, Wales, UK $ An intriguing property of afterimages is that conscious what is not perceived. A curious property of afterim- experience can be strong, weak, or absent following ages is that we do not perceive them as frequently—or identical stimulus adaptation. Previously we suggested for as long, as we ought to—based purely on the degree that postadaptation retinal signals are inherently of adaptation. Indeed, if our perception of afterimages ambiguous, and therefore the perception they evoke is correlated perfectly with the adaptation that produces strongly influenced by cues that increase or decrease the them, we would perceive them very often in the real likelihood that they represent real objects (the signal world, whereas in reality we perceive them rarely. ambiguity theory). Here we provide a more definitive Furthermore, they would not fluctuate in and out of test of this theory using two cues previously found to awareness as they often do (Comby, 1909; Wade, 1978). influence afterimage perception in opposite ways and plausibly at separate loci of action. However, by This perceptual instability is reminiscent of the manipulating both cues simultaneously, we found that alternating perceptual interpretations observed during their effects interacted, consistent with the idea that binocular rivalry or when viewing bistable figures.
    [Show full text]
  • The Saccadic System
    Chapter 3 The Saccadic System THE PURPOSE OF SACCADES The Role of the Basal Ganglia BEHAVIOR OF THE SACCADIC SYSTEM The Cerebellar Contribution to Saccades Saccadic Velocity and Duration MODELS FOR SACCADE GENERATION Saccadic Waveform ADAPTIVE CONTROL OF SACCADIC Saccadic Trajectory ACCURACY Saccadic Reaction Time (Latency) SACCADES AND MOVEMENTS OF THE Saccadic Accuracy EYELIDS Quantitative Aspects of Quick Phases of EXAMINATION OF SACCADES Nystagmus Clinical Examination of Saccades Ballistic Nature of Saccadic Movements Measurement of Saccadic Eye Saccades during Visual Search and Reading Movements Visual Consequences of Saccades PATHOPHYSIOLOGY OF SACCADIC NEUROPHYSIOLOGY OF SACCADIC EYE ABNORMALITIES MOVEMENTS Disorders of Saccadic Velocity Brainstem Pathways for Saccades Disorders of Saccadic Accuracy Higher-Level Control of the Saccadic Pulse Prematurely Terminated Saccades Generator Disorders of Saccadic Initiation Superior Colliculus Inappropriate Saccades: Saccadic The Role of the Frontal Lobe Intrusions and Oscillations The Role of the Parietal Lobe SUMMARY The Role of the Thalamus THE PURPOSE OF SACCADES REM sleep.782 Abnormalities of saccades are often distinctive and point to disorders of spe- Saccades are rapid eye movements that shift cific mechanisms. Thus, saccades have become the line of sight between successive points of an important research tool to study a wide fixation (Fig. 3–1). The term saccade is French range of issues in the neurosciences.392 in origin, referring to the jerking of a horse’s Dodge,157 working with J.J. Cogan, the head by a tug on the reins or to the flicking of father of David G. Cogan, in the early 20th a sail in a gust of wind.
    [Show full text]