Visual Processing Disorders Research Articles

Independent Deficits of Visual Word and Motion Processing in Aging and Early Alzheimer's Disease

We tested whether visual processing impairments in aging and Alzheimer's disease (AD) reflect uniform posterior cortical decline, or independent disorders of visual processing for reading and navigation. Young and older normal controls were compared to early AD patients using psychophysical measures of visual word and motion processing. We find elevated perceptual thresholds for letters and word discrimination from young normal controls, to older normal controls, to early AD patients. Across subject groups, visual motion processing showed a similar pattern of increasing thresholds, with the greatest impact on radial pattern motion perception. Combined analyses show that letter, word, and motion processing impairments are independent of each other. Aging and AD may be accompanied by independent impairments of visual processing for reading and navigation. This suggests separate underlying disorders and highlights the need for comprehensive evaluations to detect early deficits.

Books Received

Neuro-Ophthalmology: Handbook of Clinical Neurology, Vol 102Figure: Caption Not Available.Christopher Kennard and R. John Leigh. Elsevier; 2011, 544 pages, hardcover, 18 chapters. $275 ISBN-10: 0-444-52903-9 ISBN-13: 978-0-444-52903-9 Referenced Intended audience: Neuro-ophthalmologists, ophthalmologists, neurologists, neurosurgeons, residents, and fellows. This multiauthored text, written by a distinguished array of international contributors, is beautifully written and illustrated. The text begins with the anatomy and physiology of the afferent visual system and ocular motor system, followed by a neuro-ophthalmological examination. Subsequent chapters include disorders of the retina, optic nerve, chiasm, tracts, radiations, and occipital lobes. The book also reviews disorders of higher visual processing, rehabilitation techniques, and ocular motor disorders in great detail, as one would expect with Dr. Leigh as the author of the nystagmus chapter and Dr. Kennard as the author of the chapter on disorders of higher gaze control. Each easy-to-read chapter is very well organized and clearly labeled with multiple color and black-and-white figures and photographs throughout. The relevant neuroanatomy, signs and symptoms, pathophysiology, diagnostic studies, and management are reviewed. The line drawings, face photographs, anatomical illustrations, retinal photography, and neuroimaging are of very high quality. There is an extensive list of up-to-date references with each chapter. Overall, this authoritative text outlines the advances that have occurred in clinical neurology, ophthalmology, and the neurosciences and their impact on patient care. Michael S. Vaphiades, DO Department of Ophthalmology University of Alabama at Birmingham Birmingham, Alabama Paraneoplastic SyndromesFigure: Caption Not Available.Robert B. Darnell, MD, Jerome B. Posner, MD. New York, Oxford University Press; 2011, 496 pages, hardcover, 17 chapters. $145 ISBN-10: 0-199-77273-8 ISBN-13: 978-0-199-77273-5 Referenced Intended audience: Neurologists, oncologists, and neuro-ophthalmologists. While paraneoplastic syndromes (PNS) generally have been thought to be rare, after reading this book, you will realize that PNS are probably not a rare occurrence. They generally affect the endocrine and vascular systems and secondarily, the nervous system, including the visual pathways. Often, the PNS can precede detection of a cancer and are thought to be due to immune mechanisms. With moderate immunotherapy, effective treatment can be given independently of the underlying malignancy. This textbook is divided into 4 sections and 17 chapters. The first section deals with definitions and classifications of NS. The second describes the primary neurologic disorders associated with PNS. The third deals with paraneoplastic antibodies, and the fourth deals with specific tumors that cause PNS. I found this book to be incredibly well written and full of fascinating details and case histories about neurologic disease that are part of PNS disorders. It is well illustrated and cross-referenced. Although there are some redundancies, they actually help the reader in understanding that a given tumor can express antigens giving rise to different antibodies, and a given antibody can arise from several different tumors. Jerome B. Posner, MD, co-authored the text with Robert B. Darnell, MD, both international authorities in PNS. This book should be part of the library of physicians dealing with neoplastic disorders, including neurologists, oncologists, and neuro-ophthalmologists. Although much has been written over the years about PNS, this is the first comprehensive monograph devoted to this subject. John L. Keltner, MD Director of Research & Faculty Development UC Davis Health System Sacramento, California

Blast exposure and dual sensory impairment: An evidence review and integrated rehabilitation approach

Combat exposures to blast can result in both peripheral damage to the ears and eyes and central damage to the auditory and visual processing areas in the brain. The functional effects of the latter include visual, auditory, and cognitive processing difficulties that manifest as deficits in attention, memory, and problem solving--symptoms similar to those seen in individuals with visual and auditory processing disorders. Coexisting damage to the auditory and visual system is referred to as dual sensory impairment (DSI). The number of Operation Iraqi Freedom/Operation Enduring Freedom Veterans with DSI is vast; yet currently no established models or guidelines exist for assessment, rehabilitation, or service-delivery practice. In this article, we review the current state of knowledge regarding blast exposure and DSI and outline the many unknowns in this area. Further, we propose a model for clinical assessment and rehabilitation of blast-related DSI that includes development of a coordinated team-based approach to target activity limitations and participation restrictions in order to enhance reintegration, recovery, and quality of life.

Colour vision in adult amblyopia

AbstractPurpose Amblyopia is a disorder of visual processing. There is evidence that the parvocellular pathway, which prefers chromatic stimuli, is selectively damaged in amblyopia. Consistent with this hypothesis, previous studies have demonstrated that patients with amblyopia show poorer performance on colour vision tests.Methods Ten adult amblyopic subjects (3 strabismic, 5 anisometropic and 3 mixed) were tested using the Farnsworth Munsell 100 Hue (FM100Hue)colour vision test. In separate testing sessions, positive spherical lenses were used to induce blur in the fellow eye (FFE)to match the near acuity of the amblyopic eye (AME). The test (all boxes)was performed under five conditions(randomised): AME,FFE,binocularly (BIN),FFE with blur and BIN with the FFE blurred. Age matched controls were included to assess the effect of defocus in normal subjects, with blur placed in front of the non‐dominant eye to induce mild, moderate or severe blur.Results Amblyopic participants performed well in the FM100Hue test, with scores falling within normal age means in 9/11 subjects (in the AME). Strabismic amblyopes had a more pronounced deficit in error scores. Across all amblyopic subjects, performance was significantly beter under BIN conditions (p=0.023). Induced blur in controls only affected error scores under the severe blur condition, and had litle effect in amblyopic participants.Conclusion This study has shown that amblyopes perform well in this commonly performed colour vision test, and demonstrated improved test performance under binocular conditions. The low spatial frequency of the stimuli may allow for extensive pooling of chromatic information therefore allowing performance of this test to be robust to a parvocellular dysfunction.

A visual processing but no phonological disorder in a child with mixed dyslexia

The case study of Martial, a French 9-year-old boy, who exhibits severe mixed dyslexia and surface dysgraphia is reported. Despite very poor pseudo-word reading, Martial has preserved phonological processing skills as his good oral language, good phoneme awareness and good verbal short-term memory show. He exhibited a strong length effect when reading briefly presented words but no sign of mini-neglect. His letter-string processing abilities were assessed through tasks of whole and partial report. In whole report, Martial could only name a few letters from briefly displayed 5-consonant strings. He showed an initial-position advantage and a sharper than expected left-to-right gradient of performance. He performed better when asked to report a single cued letter within the string but then showed an atypical right-side advantage. The same rightward attentional bias was observed in whole report when top-down control was prevented. Otherwise, Martial showed preserved single letter identification skills and good processing of 5-letter strings when letters were sequentially displayed one at a time. His poor letter-string processing thus reflects a parallel visual processing disorder that is compatible with either a visual attention (VA) span or a visual short-term memory disorder. Martial was further engaged in a complex reaching movement task involving VA and simultaneous processing. He performed motor sequences not as a whole but as a succession of independent motor units, suggesting that his attention was not allocated in parallel to the two to-be-reached targets prior to movement execution. Against a more basic motor disorder however, he showed good performance in a task of cyclical pointing movements. The overall findings suggest that Martial suffers from a visual simultaneous processing disorder that disturbs letter identification in strings. Instead of being restricted to letter-string processing, this VA disorder might extend to non-verbal task.

Important Cofactors

The article described very competently the diagnostic evaluation and therapy of dyslexia from the perspective of child and adolescent psychiatry. In order to be able to assess the child in its entire cognitive-language learning development and not only with regard to the acquisition of written language competencies, the importance of peripheral auditory disorders, peripheral visual disorders, and auditory and visual processing and perception disorders should not be forgotten. As an example, peripheral auditory disorders —especially unilateral or minimal hearing impairments—have been confirmed to affect the quality of performance at school (1), so that the relevant diagnostic evaluation of peripheral auditory ability should be included in the diagnostic evaluation of dyslexia. Furthermore, close associations between specific language impairment and dyslexia are well known, so it seems advisable in a child with dyslexia to also test the current state of their expressive and receptive language skills development, in order to be able to include any deficits in these areas into the therapeutic concept. Finally, in case of primarily perception related spelling mistakes, diagnostic evaluation of auditory processing and perception (2) may be helpful, including performance of phonological awareness, especially as training in differentiating and identifying phonemes can have a positive effect on spelling (3), whereas, according to the current state of research, merely language-free auditory training does not yield any transfer effects for reading-spelling performance (3).

Q-ACP : un questionnaire d’évaluation des plaintes visuelles et gestuelles des patients ayant une atrophie corticale postérieure

Introduction Posterior cortical atrophy (PCA) is a clinical neurodegenerative syndrome associated with atrophy in parieto-occipital cortices, and characterized by prominent disorders of higher visual processing, affecting both dorsal and ventral streams. Methods We used a questionnaire (Q-ACP) specifically designed to assess visual and praxis dysfunctions in PCA. The Q-ACP contains 32 items (combined in 12 domains) aimed at describing everyday deficiencies that patients or caregivers notice about visual and gestural domains. It was administered to 34 patients with PCA (MMSE = 20.0 ± 5.1) which were compared with 17 patients with Alzheimer's disease (AD) (MMSE = 23.4 ± 1.9) and 31 normal controls (MMSE = 28.9 ± 1.1). Results Q-ACP of PCA patients (18.4 ± 5.3) was significantly greater than those of AD patients (2.7 ± 2.0) or normal controls (0.97 ± 1.6), and revealed disproportionate deficits on questions of visuospatial ability. Q-ACP was comparable in right (18.5 ± 4.3) and left (18.2 ± 6.8) PCA patients ( p = 0.88). There was a negative correlation between MMSE and Q-ACP in PCA patients ( r = –0.36; p = 0.045), but not in AD patients ( r = –0.21; p = 0.42). When only the 22 PCA patients with MMSE equal or greater than 20 were considered, their Q-ACP score (17.2 ± 5.3) remained significantly greater than those of AD patients and normal controls ( p = 0.0001). Controls had difficulties for only 12 of the 32 questions, and AD patients for 20 questions, whereas each of the 32 questions could be abnormal in the PCA group. The less often reported difficulties by PCA patients were for more easily reading small than big letters (14.7 %) whereas the most frequently impaired questions were for spatial and apractic agraphia (88.2 % for each question). Of the 12 domains of Q-ACP, all were impaired in PCA patients, 11 in AD patients and seven in controls. Conclusion Q-ACP is a useful tool for assessing visual and praxis everyday difficulties of patients with PCA. These difficulties are rarely observed in normal aged controls or patients with mild AD.

The Evolution of Alexia in Two Cases of Posterior Cortical Atrophy

Posterior cortical atrophy (PCA) is an uncommon presentation of Alzheimer's disease (AD), characterised by prevalent anatomo-functional involvement of posterior cortical areas. Accordingly, the main clinical features at onset are disorders of high-order visual processing, such as alexia and impairments of visuo-spatial and visuo-constructional abilities. The clinical features in the early stages of disease are variable, and they have been suggested to stem from prevalent ventral or dorsal brain pathology, and/or asymmetric hemispheric involvement. With disease progression, these differences tend to blur with the increasing severity of neuropsychological dysfunction. We report two PCA patients showing different patterns of reading impairment (respectively, letter-by-letter reading and neglect dyslexia). A follow-up study suggested that the qualitative features of alexia remain distinctive with disease evolution. In addition, single photon emission tomography (SPECT) studies revealed different patterns of hypoperfusion, consistent with the alexia types. A careful reading assessment can provide important insights to the pattern of progression of the disease in patients with PCA up to the late stages of the pathology.

The evolution of alexia in two cases of posterior cortical atrophy.

Posterior cortical atrophy (PCA) is an uncommon presentation of Alzheimer's disease (AD), characterised by prevalent anatomo-functional involvement of posterior cortical areas. Accordingly, the main clinical features at onset are disorders of high-order visual processing, such as alexia and impairments of visuo-spatial and visuo-constructional abilities. The clinical features in the early stages of disease are variable, and they have been suggested to stem from prevalent ventral or dorsal brain pathology, and/or asymmetric hemispheric involvement. With disease progression, these differences tend to blur with the increasing severity of neuropsychological dysfunction. We report two PCA patients showing different patterns of reading impairment (respectively, letter-by-letter reading and neglect dyslexia). A follow-up study suggested that the qualitative features of alexia remain distinctive with disease evolution. In addition, single photon emission tomography (SPECT) studies revealed different patterns of hypoperfusion, consistent with the alexia types. A careful reading assessment can provide important insights to the pattern of progression of the disease in patients with PCA up to the late stages of the pathology.

Assessment of Visual Processing Disorders in Children with Other Disabilities

Visual processing disorders are a common hidden problem of children with a more visible disability, which is considered to be the primary disability even if it may affect the development and learning of the child less than his impaired vision. Early diagnosis, early intervention and thorough assessment of visual processing problems require transdisciplinary working of physicians, child's therapists and teachers, orthoptists, vision rehabilitation optometrists, psychologists, and early intervention and rehabilitation teams.

The cognitive profile of posterior cortical atrophy

Posterior cortical atrophy (PCA) is a progressive dementia characterized by prominent disorders of higher visual processing, affecting both dorsal and ve. PCA patients often complain of difficulty reading and usually present initially to the ophthalmologist. The aim of this study was to define the cognitive profile of PCA and compare it to the typical Alzheimer dementia (AD). The authors used standard cognitive tests and a novel battery designed to reflect dysfunction in both ventral (Object, Face and Color Agnosia Screen [OFCAS]) and dorsal (complex pictures and compound stimuli) visual streams to test 19 patients with PCA.

Visual Agnosia Revisited

Visual Agnosia (Second Edition). Martha J. Farah (Ed.). 2005. Cambridge, MA: The MIT Press/Bradford Books, 192 pp., $25.00 (PB).Martha Farah published her influential volume Visual Agnosia in 1990. As she notes in the Preface to the second edition of this book, she undertook the project in the interest of “reviewing and systematizing the case literature and posing some basic questions that could, in principle, be answered by such cases.” The first edition of Visual Agnosia accomplished her objectives. From the extraordinarily rich but often confusing body of neuropsychological data, Dr. Farah developed a comprehensive account of visual processing disorders that was both true to the clinical phenomena and informed by then-current accounts of normal vision. Her short monograph quickly gained a wide audience and has become a standard reference. It has occupied a readily accessible spot on my bookshelf for years.

Reversible cerebral vasoconstriction syndromes

Reversible cerebral vasoconstriction syndromes (RCVS) comprise a set of conditions having in common the apoplectic onset of headache mimicking subarachnoid hemorrhage, focal or multifocal neurologic deficits with a predilection for visual processing disorders, multifocal vasoconstriction on cerebral angiography, noninflammatory spinal fluid, and a generally benign prognosis. RCVS may occur in the setting of the puerperium, after intracranial surgery, in association with prescription or illicit drug use, in migraineurs, or without a clear trigger. Distinction from central nervous system vasculitis is important and is often possible using routine clinical assessment, without brain biopsy. No treatments are of proven value in RCVS. Empiric treatments include the use of calcium channel blockers, steroids, induced hypertension or blood pressure lowering, and rarely endovascular therapy. The key to successful management is accurate diagnosis and cognizance of the tendency of RCVS to resolve without long-term immunosuppressive treatment.

The cognitive profile of posterior cortical atrophy

Posterior cortical atrophy (PCA) is a progressive dementia characterized by prominent disorders of higher visual processing, affecting both dorsal and ventral streams to cause Balint's syndrome, alexia, and visual agnosia. To define the cognitive profile of PCA and compare to the typical, primary amnestic dementia of the Alzheimer's type (DAT). The authors used standard cognitive tests and a novel battery designed to reflect dysfunction in both ventral (Object, Face & Color Agnosia Screen [OFCAS]) and dorsal (complex pictures and compound stimuli) visual streams. The authors identified 19 patients with PCA and compared their performance to a matched group of patients with DAT and normal controls. Patients with PCA were younger with marked impairment in visuospatial tasks, reading, and writing but relative preservation of memory compared to DAT using standard tests. Dorsal stream signs were most prevalent among the patients with PCA with no pure ventral stream syndromes found. All novel tests distinguished reliably between subjects with complex picture descriptions and processing of compound stimuli showing the most significant differences compared to DAT. PCA is predominantly a dorsal stream syndrome, distinct from typical DAT, which involves occipitotemporal regions over time.

Neurophysiological and perceptual correlates of navigational impairment in Alzheimer's disease

We assessed visual processing related to navigational impairment in Alzheimer's disease hypothesizing that visual motion evoked responses to optic flow simulating observer self-movement would be linked to navigational performance. Mild Alzheimer's disease and older adult control subjects underwent open-field navigational testing, visual motion perceptual threshold determination and a battery of neuropsychological examinations. We recorded visual motion evoked potentials (EPs) at occipital and parietal sites during centred visual fixation. Randomly moving or stationary pattern pre-stimuli preceded horizontal motion and radial optic flow stimuli to separate motion N200s from pattern onset responses. Radial optic flow evoked N200 responses comparable with those obtained with uniform horizontal motion, despite the variety of motion directions in radial optic flow. Alzheimer's disease patients showed smaller radial optic flow N200s than older adult subjects, and these were greatly diminished when preceded by stationary dots. Combining N200 amplitudes with optic flow perceptual thresholds and contrast sensitivities yielded a strong correlation with navigational impairment in Alzheimer's disease (R2 = 0.95). We conclude that navigational impairment in Alzheimer's disease is linked to a disorder of extrastriate visual cortical motion processing reflected in specific perceptual and neurophysiological measures.

Smooth-pursuit eye movement and directional motion-contrast sensitivity in schizophrenia

Although the occurrence of visual processing and eye-movement disorders in schizophrenia have been widely recognized, their relationship with the symptoms of schizophrenia is less well understood. In two experiments the relationship between directional-motion processing and smooth-pursuit eye movement was investigated in normal observers and in groups with positive and negative symptoms in schizophrenia. The first experiment measured linear smooth-pursuit eye movement at six target velocities from 5.0 to 30.0 degrees s(-1) and the second experiment measured directional motion-contrast sensitivity at three spatial (1.0, 4.0 and 8.0 c/deg) and five temporal (0.75, 3.0, 6.0, 12.0 and 18.0 Hz) frequencies in the same groups of observers. No significant differences were found between the control and positive-symptom group in directional motion-contrast sensitivity and smooth-pursuit eye movements. In comparison, a relationship was found between a significant reduction in directional motion-contrast sensitivity and significantly reduced smooth-pursuit eye movement in the negative-symptom group and serves to further cleave the distinction between positive and negative symptoms in schizophrenia. The relationship between visual motion processing and pursuit eye movement in the negative-symptom group was explained by a disorder in directional motion processing that fails to fully engage the pursuit eye movement system and reduces smooth pursuit eye-velocity gain.

Detailed Exploration of Face-related Processing in Congenital Prosopagnosia: 1. Behavioral Findings

We show that five individuals with congenital prosopagnosia (CP) are impaired at face recognition and discrimination and do not exhibit the normal superiority for upright over inverted faces despite intact visual acuity, low-level vision and intelligence, and in the absence of any obvious neural concomitant. Interestingly, the deficit is not limited to faces: The CP individuals were also impaired at discriminating common objects and novel objects although to a lesser extent than discriminating faces. The perceptual deficit may be attributable to a more fundamental visual processing disorder; the CP individuals exhibited difficulty in deriving global configurations from simple visual stimuli, even with extended exposure duration and considerable perceptual support in the image. Deriving a global configuration from local components is more critical for faces than for other objects, perhaps accounting for the exaggerated deficit in face processing. These findings elucidate the psychological mechanisms underlying CP and support the link between configural and face processing.

Potencial evocado cognitivo en el glaucoma primario de ángulo abierto

Primary wide angle glaucoma (PWAG) is the commonest form of this disorder. It is initially asymptomatic, until there has been considerable visual field loss. Personality changes have been described in patients with wide angle glaucoma, with a significant percentage of developing dementia or a tendency to react defensively. The P300 endogenous evoked potential is related to memory/attention to work. To evaluate, in PWAG, the probable occurrence of a disorder of visual processing due to alteration in the attention/working memory and its neuronal network, using the P300 visual cognitive evoked potential in correlation with Lobo s cognitive mini exam (CME). We selected 68 patients with PWAG and 68 controls, of both sexes, aged between 50 and 65 years. The CME was done after taking the clinical history, and then an electroretinogram, visual evoked potential using the alternating dameres (ERGd and VEPd) and P300 potential (passive odd ball). Statistical analysis was done using the t test, one way ANOVA and discriminating analysis. The amplitude on ERGd and latency on VEPd were significantly altered. Patients with glaucoma had lower scores on CME. Regarding the P300 wave, latency was the most significant parameter, whilst the amplitude and site were less well defined. In PWAG a process of visual cognitive dysfunction occurs and affects memory/attention to work in a way which is not only due to the peripheral visual effect.

Increased attentional blink after focal cerebral lesions.

Once a person identifies a visual object, the ability to detect a second object is impaired for the next few hundred milliseconds. This attentional blink is reported to increase in subjects with neglect due to acute right hemisphere lesions. To examine neural substrates of the attentional blink, the authors examined the performance of 13 subjects with chronic focal brain lesions visualized by MRI and nine control subjects without neurologic impairments on a rapid serial visual presentation task that used letters as targets. Attentional blink length in the lesion group was more than twice that of controls (p < 0.05). The magnitude of the attentional blink deficit was greatest when the second target appeared 200 ms after the first target, recovering close to baseline by 1,200 ms. Abnormal attentional blink occurred (even in the absence of neglect) with lesions in the occipitotemporal areas (associated with "object" vision) and the prefrontal cortices (thought to mediate visual working memory). Attentional blink length and attentional blink magnitude measure different components of the attentional blink process. Abnormal attentional blink can occur with different chronic focal brain lesions in a network of structures for vision and attention, and it has no special status in hemispatial neglect. Abnormal attentional blink may help explain difficulties on rapid, visually demanding cognitive tasks such as reading and automobile driving and may explain performance deficits in brain damaged patients with nonspatial disorders of visual processing.

Principles of Behavioral and Cognitive Neurology, Second Edition

Principles of Behavioral and Cognitive Neurology, Second Edition