Visual agnosia

The current dominant view of the visual system is marked by the functional and anatomical dissociation between a ventral stream specialised for perception and a dorsal stream specialised for action. The "double-dissociation" between visual agnosia (VA), a deficit of visual recognition, and optic ataxia (OA), a deficit of visuo-manual guidance, considered as consecutive to ventral and dorsal damage, respectively, has provided the main argument for this dichotomic view. In the first part of this paper, we show that the currently available empirical data do not suffice to support a double-dissociation between OA and VA...

This paper questions whether affordances are allied exclusively to dorsal stream processing within the visual system, or whether in fact different affordances are subserved by functionally independent neural pathways. Using case study evidence from patients with various visual pathologies, I argue that affordances can be categorised into type based upon their respective neurological underpinning. Such categorisation has implications for the extent to which affordances are consciously perceived or non-consciously 'picked up' within the optic array, as well as whether they indicate merely potentials for action or provide necessary information in the actualisation of behaviour...

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PRIMARY OBJECTIVES: To investigate the incidence of visual perceptual impairments in a sample of patients with traumatic brain injury (TBI) using the Occupational Therapy Adult Perceptual Screening Test (OT-APST), compare incidence rates to a normative sample and explore the relationship between the presence of visual perceptual impairment and the severity of cognitive and functional impairment following TBI. RESEARCH DESIGN: Cohort study using a convenience sample of patients with TBI and a normative sample...

Size constancy was investigated in DF, a patient with visual form agnosia, using a technique based on Emmert's law of visual after-images. DF was first given a task in which she was asked to indicate the distance of a vertical surface and a task where she had to estimate the width of a series of squares (widths ranging from 5 cm to 35 cm) placed at varying distances and having a constant visual angle. In the distance estimation task, DF greatly overestimated the distance of the vertical surface placed in front of her...

To investigate whether visual field dependence-independence changed after unilateral vestibular loss, Menière's patients were tested before and after unilateral vestibular neurotomy and compared with controls. Using the rod and frame test, visual vertical perception was tested under four visual contexts (with a frame tilted either clockwise or counterclockwise, with a vertical frame, and without visual reference). Both controls and Menière's patients before unilateral vestibular loss split into visual field dependent and independent subpopulations...

In everyday life our reaching behaviour has to be guided not only by the location and properties of the target object, but also by the presence of potential obstacles in the workspace. Recent evidence from neglect and optic ataxia patients has suggested that this automatic obstacle avoidance is mediated by the dorsal, rather than the ventral, stream of visual processing. We tested this idea in two studies involving patients with visual form agnosia resulting from bilateral ventral-stream damage. In the first study, we asked patient DF to reach out and pick up a target object in the presence of obstacles placed at varying distances to the left or right of the target...

Visual form agnosia is mainly characterized by profound deficits in visual form and shape discrimination. Previous studies have shown that patients retain the capacity for coordinated motor behaviors, color naming and implicit letter perception. However, it is unknown to what extent other visual functions, such as implicit form and orientation perception, are preserved. To address these questions, we investigated a single visual form agnosic patient, X.F., in two distinct experiments. X.F.'s visual lesions were mainly localized in the bilateral occipitotemporal cortex, with the dorsal visual stream and early visual cortex largely spared...

Posterior cortical atrophy (PCA) is characterized by bilateral parieto-occipito-temporal atrophy and hypometabolism. Neuropsychological impairments include complex visual disturbances, alexia, agraphia, finger agnosia, right-left disorientation and dyscalculia. A recent case study reported severe numerical deficits with some selectively preserved numerical skills in a patient affected by PCA [Delazer, M., Karner, E., Zamarian, L., Donnemiller, E., & Benke, T. (2006). Number processing in posterior cortical atrophy--a neuropsycholgical case study...

Previous investigations of visuospatial abilities in the visual form agnosic patient D.F. suggest that her egocentric sensorimotor processing is intact while her 'allocentric' judgments of spatial position are impaired. The current investigation extends these previous observations by comparing D.F.'s performance at pointing to a set of spatially distributed stimuli, either directly or by 'pantomiming' the responses in an adjacent homologous workspace. The results showed accurate sensorimotor localization when D...

BACKGROUND: 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. OBJECTIVE: To define the cognitive profile of PCA and compare to the typical, primary amnestic dementia of the Alzheimer's type (DAT). METHODS: 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...

Cerebral visual impairment is one of the main causes of childhood visual impairment in developed countries. These disorders are often linked with pre- or perinatal hypoxic brain injuries. The patterns of brain injuries depend on the severity and duration of hypoxia and the child's age. In premature children, periventricular leukomalacia affects the optic radiations and the subcortical visual brain. In full-term newborn babies, chronic hypoxia leads to the damage of the visual cortex and acute hypoxia damages the basal ganglia...

Previous studies have shown that perirhinal cortex lesions in monkeys impair visual discriminations with a high degree of "feature ambiguity," a property of visual discriminations that can emerge when features are a part of both rewarded and unrewarded stimuli. The effects of damage to the hippocampus on these perirhinal-dependent feature-ambiguous tasks are, however, unknown. Prominent theories of medial temporal lobe function predict similar effects of perirhinal cortex and hippocampal lesions on cognitive tasks...

Patients with colour agnosia can perceive colours and are able to match coloured patches on hue, but are unable to identify or categorise colours. It is a rare condition and there is as yet no agreement on the clinical definition or a generally accepted explanation. In line with observations from object agnosia and prosopagnosia, we hypothesised that (some of) these patients might still be able to process colour information at an implicit level. In this study, we investigated this possibility of implicit access to colour semantics and colour names in a man (MAH) who suffers from developmental colour agnosia...

Computer-generated shapes varying on visual dimensions such as curvature, tapering, and thickness have been used to investigate identification deficits in the category-specific visual agnosia (CSVA) Patient E.L.M.. However, whether the implemented variations on each of these dimensions were perceived by novice observers as "similar amounts of change" is unknown. To estimate distance in psychophysical shape space, sets of shapes were developed using two different scaling methods--an objective method based on visual search, and a subjective method based on judgments of similarity--and a third approach that did not involve scaling...

Occupational therapy assessment and treatment of visual perceptual impairments are integral to the rehabilitation of clients following stroke and other acquired brain injuries. Occupational therapists need to identify the nature of visual perceptual performance impairments in order to choose rehabilitation intervention strategies appropriate for remediation of specific problems or to compensate for limitations in daily function. This paper describes the variations in visual perception terminology and occupational therapy approaches to visual perceptual assessment...

Visual-spatial agnosis, praxis deficits and hallucinations can be the features of subacute sclerosing panencephalitis (SSPE) in the early period. This study describes a 15-year-old boy with SSPE presenting with visual agnosia, prosopagnosia, simultanagnosia, optic ataxia, and oculomotor apraxia which are compatible with Balint syndrome. MRI revealed heterogenous and abnormal signal changes in the bilateral parieto-occipital areas. The signals were more prominent on the left. The case discussed herein is important because he was diagnosed as Balint's syndrome by means of clinical and neuroradiological findings before the onset of known symptomatology as dementia/myoclonus of SSPE...

Novel experiments with Ultrasound Associated with High Frequency Electromagnetic Field (UAHFEMF) irradiation on rats and mice found evidences of characteristic Alzheimer's disease (AD) degenerations including neurite plaques, beta-amyloid, TAU plaque and deposition in cells, Neuro-Fibrillary Tangle and Paired Helical Filament (PHF) with rats and mice irradiated up to 2454 hours. Concomitant passive avoidance test was performed on six mice, and all showed signs of visual and auditory agnosia and lost cognition of threatening condition...

We re-evaluated a case of carbon monoxide poisoning presenting as visual agnosia who had been injured by explosion of Miike-Mikawa coal mine 40 years ago. In an early stage, his main neuropsychological symptoms were visual agnosia, severe anterograde amnesia, alexia, agraphia, constructional apraxia, left hemispatial neglect and psychic paralysis of gaze, in addition to pyramidal and extra pyramidal signs. At the time of re-evaluation after 40 years, he still showed visual agnosia associated with agraphia and constructional apraxia...

Kluver-Bucy syndrome is a rare neurobehavioral condition characterized by visual agnosia, excessive oral tendencies, hypermetamorphosis, placidity, altered sexual behavior, and changes in dietary habits. This description of a 14-year-old boy presenting with complete Kluver-Bucy syndrome after Mycoplasma pneumoniae bronchitis is the first such case report. MRI revealed left temporal horn dilation and asymmetry of both temporal lobes. We hypothesize that the pathophysiology of our case is immune-mediated damage by M...