Color discrimination in schizophrenia

Neuropsychiatric conditions that involve dopaminergic depletion have been associated with color discrimination deficits along the blue-hue (tritan, or short-wavelength-sensitive) axis. Because dopamine dysregulation may be a major factor in schizophrenia, we investigated color vision in this disorder. The performance of males with schizophrenia (SZ, n = 16) and normal male control subjects (CS, n = 14) was evaluated on five measures of color discrimination. SZ made more hue discrimination errors than CS, but no pattern emerged regarding a hue-specific axis of deficit. Dosage of anti-psychotic medication was not correlated with performance on hue discrimination. These results suggest that in medicated patients with schizophrenia, the dopaminergic disturbance, which may involve system hyperactivity, does not produce tritan-specific color deficits that have been observed in disorders involving dopaminergic hypoactivity.

Facial frequency manipulation normalizes face discrimination in AD

People with AD have deficient contrast sensitivity and impaired face discrimination. The authors presented photographs of unfamiliar faces of three different sizes to enhance the low, middle, or high facial frequency information (cycles per face). Patients with AD demonstrated normal discrimination of small faces only, indicating that impaired contrast sensitivity at low facial frequencies contributes to their poor face discrimination.

Neuropsychological consequences of cerebellar tumour resection in children: cerebellar cognitive affective syndrome in a paediatric population

Acquired cerebellar lesions in adults have been shown to produce impairments in higher function as exemplified by the cerebellar cognitive affective syndrome. It is not yet known whether similar findings occur in children with acquired cerebellar lesions, and whether developmental factors influence their presentation. In studies to date, survivors of childhood cerebellar tumours who demonstrate long-term deficits in cognitive functions have undergone surgery as well as cranial irradiation or methotrexate treatment. Investigation of the effects of the cerebellar lesion independent of the known deleterious effects of these agents is important for understanding the role of the cerebellum in cognitive and affective development and for informing treatment and rehabilitation strategies. If the cerebellar contribution to cognition and affect is significant, then damage in childhood may influence a wide range of psychological processes, both as an immediate consequence and as these processes fail to develop normally later on. In this study we evaluated neuropsychological data in 19 children who underwent resection of cerebellar tumours but who received neither cranial irradiation nor methotrexate chemotherapy. Impairments were noted in executive function, including planning and sequencing, and in visual-spatial function, expressive language, verbal memory and modulation of affect. These deficits were common and in some cases could be dissociated from motor deficits. Lesions of the vermis in particular were associated with dysregulation of affect. Behavioural deficits were more apparent in older than younger children. These results reveal that clinically relevant neuropsychological changes may occur following cerebellar tumour resection in children. Age at the time of surgery and the site of the cerebellar lesion influence the neurobehavioural outcome. The results of the present study indicate that the cerebellar cognitive affective syndrome is evident in children as well as in adults, and they provide further clinical evidence that the cerebellum is an essential node in the distributed neural circuitry subserving higher-order behaviours.

Alzheimer-like visual deficits in Down syndrome

Patients with Alzheimer disease (AD) show visual impairments in color discrimination (blue hues), stereoacuity, and contrast sensitivity. We asked whether the AD-type visual profile occurs in Down syndrome (DS) in light of the fact that AD neuropathology is present in DS by age 40. We tested 22 adults with DS and 18 adults with mental retardation of non-DS etiology (MR). DS subjects made more tritanomalous errors on the test of color vision than predicated by chance (p < 0.05), indicating a deficiency in the discrimination of short wavelengths (blue hues) but not more of other types of hue discrimination errors. DS subjects had higher stereoacuity thresholds than MR subjects (p < 0.01) and reduced contrast sensitivity across the frequency range (p < 0.01). Taken together, the results point to AD-like visual deficits in DS. Like classic AD, DS may be associated with pathological changes in the parastriate and peristriate visual cortex. DS performance was not correlated with age, suggesting that in individual subjects, the AD-like visual deficits may present prior to and independent of age-associated dementia.

Visuospatial dysfunction and problem solving in Parkinson's disease

Individuals with Parkinson's disease (PD) perform deficiently on Raven's Coloured Progressive Matrices (RCPM), in contrast to their relatively good performance on many other problem-solving tasks. The question is raised as to whether a visuospatial deficit may account for poor RCPM performance in PD. The authors analyzed RCPM results in 50 nondemented participants with PD and 39 age-matched healthy control participants. The PD group made significantly more errors than the control group on all RCPM subtests, including the subtest that mainly assessed visuospatial function (RCPM-A). For the PD group, the composite score of other visuospatial tests, but not the composite scores of tests of executive function or verbal memory, significantly predicted performance on the RCPM-A. Visuospatial impairment in PD may arise from dysfunction of the basal ganglia-thalamocortical circuit that also includes the dorsolateral prefrontal cortex and, importantly, the posterior parietal lobes.

Visuospatial dysfunction and problem solving in Parkinson's disease

Individuals with Parkinson's disease (PD) perform deficiently on Raven's Coloured Progressive Matrices (RCPM), in contrast to their relatively good performance on many other problem-solving tasks. The question is raised as to whether a visuospatial deficit may account for poor RCPM performance in PD. The authors analyzed RCPM results in 50 nondemented participants with PD and 39 age-matched healthy control participants. The PD group made significantly more errors than the control group on all RCPM subtests, including the subtest that mainly assessed visuospatial function (RCPM-A). For the PD group, the composite score of other visuospatial tests, but not the composite scores of tests of executive function or verbal memory, significantly predicted performance on the RCPM-A. Visuospatial impairment in PD may arise from dysfunction of the basal ganglia-thalamocortical circuit that also includes the dorsolateral prefrontal cortex and, importantly, the posterior parietal lobes.

Vision in Alzheimer's disease

In order to assess vision in Alzheimer's disease (AD) and related disorders, gerontologists must use tests that make minimal cognitive demands on the subject. Using such tests, we have found a pattern of deficits in color discrimination, stereoacuity, contrast sensitivity, and backward masking that differs from that seen in healthy elderly individuals. Impaired vision predicts deficient performance of subjects with AD on numerous tests of cognition, underscoring the importance of understanding visual changes in this population.

Prevalence of visual deficits in Alzheimer's disease

This study addressed the issue of prevalence and pattern of visual deficits in 77 subjects with Alzheimer's disease (AD) and 111 healthy control subjects. We defined cutoff scores that would be expected from only 1 control subject of 100 (p = 0.01). The percentage of AD subjects who performed at or worse than this level varied across the 16 visual tests from a high of 58% to a low of 0%. The distribution of impairment across tests suggests a high vulnerability in AD of pattern vision, moderate vulnerability of spatial vision, and low vulnerability of motion and flicker perception. We found evidence for heterogeneity in the AD subject group: a subgroup (N = 14) emerged that was characterized by poor performance on the Backward Pattern Masking test, relatively young age, and relatively short duration of AD. Overall, the results indicate that visual dysfunction, especially on Backward Masking, is a common sign of AD.

Visual dysfunction predicts cognitive deficits in Alzheimer's disease

Deficits in basic visual capacities are prevalent in Alzheimer's disease (AD), raising the question of their impact on cognitive function. We examined the relation between vision and cognition in 72 patients with AD. Vision tests assessed color discrimination, stereoacuity, contrast sensitivity, and backward pattern masking. For cognitive tests of object recognition, at least 25% (up to 50%) of score variance was predicted by performance on a vision test. For tests of spatial localization, only 2 to 11% of the variance was predicted by performance on a vision test. The results indicated that: (1) visual dysfunction was a significant predictor of cognitive dysfunction in AD, and (2) visual deficits in AD may have a strong functional impact on performance in specific cognitive domains.

Impaired problem solving in Parkinson's disease: impact of a set-shifting deficit

Parkinson's disease (PD) is associated with specific cognitive deficits in the absence of dementia, including the inability to suppress previously learned responses in a changed context. Our goal was to determine whether this set-shifting deficit is sufficient to account for impaired performance on a problem-solving task, or, instead, whether it is necessary to postulate deficits in one or more other cognitive capacities, such as logical deduction. Deductive reasoning and other conceptual abilities were assessed in 15 nondemented subjects with PD who had never been medicated, 15 nondemented subjects with PD who were currently receiving medication, and 15 healthy elderly control subjects. On a deductive reasoning task, Poisoned Food Problems, the PD groups made more errors than the control group. The PD groups' error pattern was characterized by intrusions of information from previous problems. By contrast, the PD groups made appropriate assessments of redundant and irrelevant information that appeared in these problems, and performed normally on other tests of concept formation and problem solving that did not require set shifting, indicating that the capacities for logical deduction and concept formation were intact. The set-shifting deficit, conceptualized as a difficulty in suppressing a prepotent response, appears to be a primary cognitive impairment in PD and presumably arises from dysfunction of the nigrostriatal-dorsolateral prefrontal cortex complex loop.

Incomplete achromatopsia in Alzheimer's disease

We report that patients with Alzheimer's disease (AD) have a selective deficit in blue hue discrimination, as assessed with three clinical measures of color vision. The Farnsworth D-15 Test, the Lanthony New Color Test, and the City University Color Vision Test were administered to 32 patients with AD (ranging in dementia severity from mild to severe) and 32 age-matched normal control subjects (NCS). Of the AD patients, 11 who were representative of the larger group for age, education level, and dementia severity received a complete neuro-ophthalmological examination that ruled out obvious disorders of the anterior visual structures. AD patients made significantly more tritan (blue) errors than NCS on all three color vision tests but did not make more protan (red) or deutan (green) errors on two of the three tests. The results support the conclusion that there is a deficit in color discrimination in AD that is specific to blue hues, and oppose the hypothesis that AD does not deleteriously affect the color-opponent visual channel. In the absence of obvious damage to anterior visual structures, the likely substrates for the observed deficit are peristriate and inferotemporal visual cortices, which are subject to significant neuropathology in AD.

Retinocalcarine function in Alzheimer's disease. A clinical and electrophysiological study

Impaired visual function in Alzheimer's disease (AD) could result from either precortical or cortical lesions, or both. In a parallel psychophysical study of visual function in AD, we found that contrast sensitivity function, color vision, stereoacuity, and backward masking were impaired relative to the performance of age-matched control subjects, whereas performance on a critical flicker fusion test was normal. The intent of the present study was to determine whether abnormalities of the retinocalcarine pathway contribute to visual dysfunction. We performed neuro-ophthalmological examinations on 38 patients with AD; from this group, 25 received additional psychophysical testing and 13 underwent electrophysiological testing. Clinical neuro-ophthalmological examinations, full-field electroretinograms, focal electroretinograms, and pattern visual evoked potentials were normal in all patients tested. There was no evidence of retinocalcarine abnormality specific to AD. We conclude that the visual impairment experienced by some patients with AD primarily results from involvement of the visual association cortices rather than from precortical damage, at least before the end stage of the disease.

Category knowledge in Alzheimer's disease: Normal organization and a general retrieval deficit

Three hypotheses that could account for deficits in the retrieval of category information in Alzheimer's disease (AD) were evaluated: abnormal organization, class- or category-specific vulnerability, and limitation by general factors, such as decreased processing speed. Relative to 18 elderly control subjects, 18 patients with AD produced fewer items in a category fluency task and had longer reaction times in a category decision task. The pattern of performance across categories on both tasks was normal in the AD group: The same categories elicited the most (or fastest) responses in both the control group and the AD group. AD patients showed normal performance in ranking of category exemplars by typicality. There was no evidence for differential accessibility by category or by class of information (animate vs. inanimate). The authors conclude that a general factor or factors limit(s) retrievability equally across all categories.

Visual function in Alzheimer's disease and normal aging

We examined a wide range of visual behaviors in 59 patients with Alzheimer's disease (AD), 35 elderly control subjects, and 12 young control subjects. A subset of the patients with AD received neuro-ophthalmologic and electrophysiologic examinations in order to evaluate the integrity of the retino-calcarine pathway. Patients with AD showed significant, selective losses in visual function, including color discrimination, stereoacuity, contrast sensitivity, and backward masking, but not in critical flicker fusion. The deficits were not attributable to clinically apparent lesions of the retina or optic nerve. We therefore suggest that AD lesions in primary visual and posterior association cortices underlie the observed behavioral abnormalities.

Visual dysfunction in Alzheimer's disease: relation to normal aging

In patients with Alzheimer's disease (AD), compared with age-matched and young healthy control subjects, visual deficits in the following functions were observed: color, stereoacuity, contrast sensitivity, and backward masking (homogeneous and pattern). Critical flicker fusion thresholds were normal, relative to age-matched healthy subjects. For color, the majority of the errors were tritanomalous (blue axis). Color and stereoacuity deficits were unrelated to severity of dementia, in accordance with models of vision that describe these functions as modular rather than diffuse for cortical localization. Although contrast sensitivity was depressed throughout the frequency range in AD, more patients were impaired at low than at high spatial frequencies, contrasting with the observed normal aging pattern of high-frequency loss. Healthy elderly subjects showed depressed critical flicker fusion thresholds and reduced contrast sensitivity at high frequencies, relative to the young group; differences between these groups were not found for the other vision tests. A subset of the AD group received detailed neuro-ophthalmological examination, and no abnormalities were found. This finding, taken together with normal thresholds for critical flicker fusion, suggests that the widespread visual dysfunction reported here is more likely to be related to known pathological changes in primary visual and association cortex in AD than to changes in the retina or optic nerve.

Subcortical transfer of cognitive information in subjects with complete forebrain commissurotomy

Three complete commissurotomy subjects were tested for the ability to integrate cognitive information presented for a prolonged duration to opposite visual hemi-fields. A sample stimulus was projected to one hemi-field and a three-choice array to the other, with one choice related to the sample on an abstract or concrete basis. All subjects performed the non-verbal matching task at well above chance level, with scores comparable to those attained when the task was performed completely within one or the other hemisphere. Transfer was equally successful in the two directions, though the pathway originating in the right and terminating in the left hemisphere may be more sensitive to affective components of the stimulus. The information relayed subcortically is neither verbal nor imagic in nature, but appears to correspond to contextual or connotative associates of the stimulus. The results are discussed in terms of a cognitive system common to the two hemispheres and involving associational networks but not lateralized functions such as language and complex visuospatial processes.

Figure-background perception in right and left hemispheres of human commissurotomy subjects

The right and left hemispheres of four complete commissurotomy subjects were tested for the ability to recognize and integrate figure and background elements of composite visual stimuli. In the first experiment the subjects were required to identify from a four-choice array in free vision the stimulus card that matched the briefly lateralized sample stimulus. For all subjects the left hemispheres was proficient at identifying the figure, but performed at near-chance level in recognizing the textured background. In contrast, the right hemisphere was equally adapt at identifying figures and backgrounds. Both hemispheres could easily identify the isolated figure or background from a choice array, demonstrating that the observed hemisphere effects were due to figure-background interactions rather than the result of any difficulty in processing specific elements of the composite stimulus. The second experiment involved the determination of the size and position of a dot that appeared against various plain and textured backgrounds. The right hemisphere of two subjects, but not the left, performed with greater accuracy when the background consisted of a 'natural' texture gradient rather than a plain white backing. Similar though less consistent results were obtained when an inverted gradient or an evenly spaced grid was used as the background. For each condition, right-hemisphere performance resembled that of normal control subjects. In contrast, the left hemisphere provided a pattern of results dissimilar to that of control subjects for the various figure-background tasks described. It appeared to be generally insensitive to background effects, except when the information provided by the background was highly unusual, as from an inverted texture gradient. The results suggest a preeminent role for the right hemisphere in the recognition of background components of a whole-field stimulus, sensitivity to the influence of the background on the perception of an object, and the ability to use natural perspective cues to assist in the accurate perception of an object.

Perception of apparent motion by commissurotomy patients

When two spatially separated light spots are flashed in rapid succession, the spot will appear to move between the two locations--an illusion called apparent motion. We have presented this display to callosum-sectioned human patients and found that they could correctly report the temporal order of a simple apparent motion sequence presented across the vertical meridian. Hence, the forebrain commissures are not required for this function.

Comprehension of abstract concepts in right and left hemispheres of complete commissurotomy subjects

The left and right hemispheres of three complete commissurotomy subjects were tested for the ability to comprehend abstract concepts. A technique was used which allows prolonged viewing of stimulus material restricted to a single visual hemi-field. Twenty-three trials involving a sample inspection figure and a three-choice answer array were presented to each hemi-field with instructions to point to the one picture in the choice array related to the sample. As none of the possible choices matched the sample stimulus on any concrete level, correct responses required an abstract mental association. Both the verbal and non-verbal hemispheres performed the task at a high level of proficiency in all subjects. It was further noted that both commissurotomy and normal subjects experienced difficulty in articulating the involved abstract relationship when asked to do so under a free vision condition. The results demonstrate that the right hemisphere, lacking a highly developed language system, can nevertheless support sophisticated cognitive processing at an abstract level, and further suggest that the associative process is not necessarily language-mediated in either hemisphere.