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Ophthalmology Clinics of North America Mar 2001Lesions of extrastriate cortex cause selective defects in visual function. Damage to portions of the "ventral stream" in medial and inferior occipitotemporal cortex lead... (Review)
Review
Lesions of extrastriate cortex cause selective defects in visual function. Damage to portions of the "ventral stream" in medial and inferior occipitotemporal cortex lead to impaired perception of color or various specific visual object recognition defects, such as prospagnosia, the inability to recognize familiar faces, and alexia, the inability to read. The latter must be distinguished from a variety of other reading defects related to primary visual, attentional, linguistic, or ocular motor impairments. Damage to the "dorsal stream" in lateral occipito-temporo-parietal regions impairs visuospatial capabilities, leading to akinetopsia (impaired motion perception) or Balint's syndrome, a loosely bound triad of simultanagnosia, optic ataxia, and ocular motor apraxia. Topographagnosia can occur with ventral or dorsoal lesions for different reasons. Considerable evidence has accumulated showing that residual vision or even "blindsight," which is visual perception in the absence of awareness, can persist after lesion of striate cortex in some patients.
Topics: Brain Diseases; Humans; Perceptual Disorders; Visual Cortex; Visual Pathways
PubMed: 11370568
DOI: No ID Found -
Handbook of Clinical Neurology 2021The term visual agnosia is used to refer to recognition disorders that are confined to the visual modality, that are not due to an impairment in sensory functions, and...
The term visual agnosia is used to refer to recognition disorders that are confined to the visual modality, that are not due to an impairment in sensory functions, and that cannot be explained by other cognitive deficits or by general reduction in intellectual ability. Here, we describe the different types of visual agnosia that have been reported (form agnosia, integrative agnosia, associative agnosia, transformational and orientation agnosia as well as category-specific impairments such as pure alexia and prosopagnosia) and how they relate to the current understanding of visual object recognition. Together with related disorders such as simultanagnosia, texture agnosia, aphantasia, and optic aphasia, these visual perceptual impairments can have severe consequences for those affected. We suggest how in-depth assessment can be carried out to determine the type and the extent of these impairments. In the context of clinical assessment, a step-by-step approach reflecting a posterior to anterior gradient in visual object recognition, from more perceptual to more memory-related processes, is suggested. Individually tailored interventions targeting the identified impairments can be initiated based on the results of the assessment.
Topics: Agnosia; Cognition Disorders; Humans; Neuropsychological Tests; Orientation; Visual Perception
PubMed: 33832675
DOI: 10.1016/B978-0-12-821377-3.00008-8 -
Current Neurology and Neuroscience... Nov 2006Posterior cortical atrophy is a striking clinical syndrome in which a dementing illness begins with visual symptoms. Initially, the problem may seem to be loss of... (Review)
Review
Posterior cortical atrophy is a striking clinical syndrome in which a dementing illness begins with visual symptoms. Initially, the problem may seem to be loss of elementary vision, but over time the patient develops features of visual agnosia, topographical difficulty, optic ataxia, simultanagnosia, ocular apraxia (Balint's syndrome), alexia, acalculia, right-left confusion, and agraphia (Gerstmann's syndrome), and later a more generalized dementia. Occasional patients have visual hallucinations and signs of Parkinson's disease or Lewy body dementia. A number of different neuropathologic disorders are associated with posterior cortical atrophy.
Topics: Atrophy; Brain Diseases; Cerebral Cortex; Humans
PubMed: 17074282
DOI: 10.1007/s11910-006-0049-0 -
Experimental Brain Research Apr 2010Patients with simultanagnosia, which is a component of Bálint syndrome, have a restricted spatial window of visual attention and cannot see more than one object at a...
Patients with simultanagnosia, which is a component of Bálint syndrome, have a restricted spatial window of visual attention and cannot see more than one object at a time. As a result, these patients see the world in a piecemeal fashion, seeing the local components of objects or scenes at the expense of the global picture. To directly test the relationship between the restriction of the attentional window in simultanagnosia and patients' difficulty with global-level processing, we used a gaze-contingent display to create a literal restriction of vision for healthy participants while they performed a global/local identification task. Participants in this viewing condition were instructed to identify the global and local aspects of hierarchical letter stimuli of different sizes and densities. They performed well at the local identification task, and their patterns of inaccuracies for the global level task were highly similar to the pattern of inaccuracies typically seen with simultanagnosic patients. This suggests that a restricted spatial area of visual processing, combined with normal limits to visual processing, can lead to difficulties with global-level perception.
Topics: Adolescent; Adult; Attention; Brain; Female; Humans; Magnetic Resonance Imaging; Male; Middle Aged; Neuropsychological Tests; Pattern Recognition, Visual; Perceptual Disorders; Recognition, Psychology; Visual Perception; Young Adult
PubMed: 20066404
DOI: 10.1007/s00221-009-2152-3 -
Cortex; a Journal Devoted To the Study... Jun 2011We examined the effects of different grouping cues (item density, number and connectedness) on the ability of a patient with simultanagnosia (GK) to identify compound...
We examined the effects of different grouping cues (item density, number and connectedness) on the ability of a patient with simultanagnosia (GK) to identify compound stimuli. In Experiment 1, the effects of density and connectedness on the recognition of global and local forms were examined. In Experiment 2, the spatial distance of local elements was manipulated by varying the size of the global forms and the number of local elements, to assess whether the distance between the local elements or their number determined the effects on global/local processing in disconnected patterns. The results showed that high item density and connectedness, each facilitates the grouping of local elements into global shapes, determined the explicit recognition of global stimuli in simultanagnosia. Moreover, in addition to any bias to attend to the local level, there was also evidence for attentional capture by stimuli at the global level. The data indicate that grouping processes still operate in simultanagnosia and can overcome biases to select at a local level. Any biases in selection can also be compounded by poor attentional disengagement.
Topics: Aged; Agnosia; Analysis of Variance; Attention; Humans; Male; Middle Aged; Pattern Recognition, Visual; Photic Stimulation; Reaction Time; Visual Perception
PubMed: 20674891
DOI: 10.1016/j.cortex.2010.05.007 -
Brain Research. Cognitive Brain Research Dec 1995Visual evoked potentials (VEPs) to central and lateral half field patterned stimuli of 1, 2 and 4 cycles per degree (cpd) were recorded in a patient with Dorsal...
Visual evoked potentials (VEPs) to central and lateral half field patterned stimuli of 1, 2 and 4 cycles per degree (cpd) were recorded in a patient with Dorsal Simultanagnosia due to bilateral lesions of parieto-occipital junction. VEPs consisted of the normal N1-P1-N2 components with same spatial frequency sensitivity as in controls. VEPs had similar latencies and amplitudes whether the patient could see or not the patterned stimuli. Event related potentials (ERPs) to visual and acoustic odd-ball paradigm were also recorded in the same patient. Visual ERPs consisted of an early NA-effect, and of N2-P3 components. P3 was recorded only from frontal, central and temporal derivations. The topographical P3 abnormality was, however, the same for visual and acoustic odd-ball paradigms. The amplitude of P3 was smaller when the patient missed visual stimuli. These findings show that severe bilateral lesions at the parieto-occipital junction, inducing Simultanagnosia, do not obliterate VEPs or ERPs components.
Topics: Acoustic Stimulation; Aged; Electroencephalography; Evoked Potentials, Visual; Female; Humans; Photic Stimulation; Reaction Time; Tomography, Emission-Computed, Single-Photon; Tomography, X-Ray Computed; Vision Disorders
PubMed: 8719019
DOI: 10.1016/0926-6410(95)00015-1 -
Journal of Neurology, Neurosurgery, and... Feb 2002From a series of glimpses, we perceive a seamless and richly detailed visual world. Cerebral damage, however, can destroy this illusion. In the case of Bálint's... (Review)
Review
OBJECTIVES
From a series of glimpses, we perceive a seamless and richly detailed visual world. Cerebral damage, however, can destroy this illusion. In the case of Bálint's syndrome, the visual world is perceived erratically, as a series of single objects. The goal of this review is to explore a range of psychological and anatomical explanations for this striking visual disorder and to propose new directions for interpreting the findings in Bálint's syndrome and related cerebral disorders of visual processing.
METHODS
Bálint's syndrome is reviewed in the light of current concepts and methodologies of vision research.
RESULTS
The syndrome affects visual perception (causing simultanagnosia/visual disorientation) and visual control of eye and hand movement (causing ocular apraxia and optic ataxia). Although it has been generally construed as a biparietal syndrome causing an inability to see more than one object at a time, other lesions and mechanisms are also possible. Key syndrome components are dissociable and comprise a range of disturbances that overlap the hemineglect syndrome. Inouye's observations in similar cases, beginning in 1900, antedated Bálint's initial report. Because Bálint's syndrome is not common and is difficult to assess with standard clinical tools, the literature is dominated by case reports and confounded by case selection bias, non-uniform application of operational definitions, inadequate study of basic vision, poor lesion localisation, and failure to distinguish between deficits in the acute and chronic phases of recovery.
CONCLUSIONS
Studies of Bálint's syndrome have provided unique evidence on neural substrates for attention, perception, and visuomotor control. Future studies should address possible underlying psychoanatomical mechanisms at "bottom up" and "top down" levels, and should specifically consider visual working memory and attention (including object based attention) as well as systems for identification of object structure and depth from binocular stereopsis, kinetic depth, motion parallax, eye movement signals, and other cues.
Topics: Agnosia; Attention; Brain Mapping; Cerebrovascular Disorders; Dominance, Cerebral; Humans; Occipital Lobe; Perceptual Disorders; Psychomotor Disorders; Visual Cortex; Visual Perception
PubMed: 11796765
DOI: 10.1136/jnnp.72.2.162 -
Neurology Oct 1987We studied three subjects who reported the apparent "disappearance" of stationary objects from direct view. They had simultanagnosia caused by CT-verified bilateral...
We studied three subjects who reported the apparent "disappearance" of stationary objects from direct view. They had simultanagnosia caused by CT-verified bilateral superior occipital lobe lesions. They had no abnormalities of visual acuity or fields to explain their defect. EOG with computer analysis showed intact motility and scanning. Most important, the subjects reported intermittent disappearance of a light target during EOG-verified fixation--ie, they were looking but not seeing. Results indicate that attention mechanisms that permit sustained awareness of visual targets depend on the superior visual association cortices and are relatively separate from mechanisms that shift gaze and drive visual search.
Topics: Aged; Agnosia; Attention; Electrooculography; Eye Movements; Fixation, Ocular; Humans; Male; Middle Aged; Psychomotor Performance; Tomography, X-Ray Computed; Vision, Ocular; Visual Perception
PubMed: 3658172
DOI: 10.1212/wnl.37.10.1642 -
Cortex; a Journal Devoted To the Study... 2013Maps, graphs, and diagrams use simplified graphic forms, like lines and blobs, to represent basic spatial relations, like boundaries and enclosures. A schema is an...
Maps, graphs, and diagrams use simplified graphic forms, like lines and blobs, to represent basic spatial relations, like boundaries and enclosures. A schema is an iconic representation where perceptual detail has been abstracted away from reality in order to provide a more flexible structure for cognition. Unlike truly symbolic representations of spatial relations (i.e., prepositions) a schema preserves some analog spatial qualities of the relation it stands in for. We tested the efficacy of schemas in facilitating the perception and comprehension of spatial relations in a patient with bilateral occipitoparietal damage and resulting simultanagnosia. Patient E.E. performed six matching tasks involving WORDS (in, on, above, below), photographic PICTURES of objects, and/or SCHEMAS depicting the same spatial relations. E.E. was instructed to match a single spatial relation to a corresponding image from an array of four choices. On the two tasks that did not include matching to or from schemas, E.E. performed at chance levels. On tasks with schemas, performance was significantly better, indicating that schematic representations make spatial relations visible in a manner that symbols and complex images do not. The results provide general insight as to how schemas facilitate spatial reasoning when used in graphic depictions, and how such theoretically intermediate representational structures could serve to link perceptual and verbal representations of spatial relations in the brain.
Topics: Adult; Awareness; Cerebral Infarction; Cognition Disorders; Color; Female; Humans; Photic Stimulation; Psychomotor Performance; Semantics; Space Perception
PubMed: 23643246
DOI: 10.1016/j.cortex.2013.03.005 -
The European Journal of Neuroscience Jan 2009Patients with bilateral parieto-occipital brain damage may show intact processing of individual objects, while their perception of multiple objects is disturbed at the...
Patients with bilateral parieto-occipital brain damage may show intact processing of individual objects, while their perception of multiple objects is disturbed at the same time. The deficit is termed 'simultanagnosia' and has been discussed in the context of restricted visual working memory and impaired visuo-spatial attention. Recent observations indicated that the recognition of global shapes can be modulated by the spatial distance between individual objects in patients with simultanagnosia and thus is not an all-or-nothing phenomenon depending on spatial continuity. However, grouping mechanisms not only require the spatial integration of visual information, but also involve integration processes over time. The present study investigated motion-defined integration mechanisms in two patients with simultanagnosia. We applied hierarchical organized stimuli of global objects that consisted of coherently moving dots ('shape-from-motion'). In addition, we tested the patients' ability to recognize biological motion by presenting characteristic human movements ('point-light-walker'). The data revealed largely preserved perception of biological motion, while the perception of motion-defined shapes was impaired. Our findings suggest separate mechanisms underlying the recognition of biological motion and shapes defined by coherently moving dots. They thus argue against a restriction in the overall capacity of visual working memory over time as a general explanation for the impaired global shape recognition in patients with simultanagnosia.
Topics: Aged; Agnosia; Brain Damage, Chronic; Brain Mapping; Female; Fluorodeoxyglucose F18; Glucose; Humans; Magnetic Resonance Imaging; Male; Memory, Short-Term; Middle Aged; Motion Perception; Neuropsychological Tests; Parietal Lobe; Pattern Recognition, Visual; Perceptual Disorders; Photic Stimulation; Positron-Emission Tomography; Visual Cortex; Visual Pathways
PubMed: 19120445
DOI: 10.1111/j.1460-9568.2008.06559.x