Glossary

alexia An acquired condition, usually as a result of brain damage (such as follows strokes in adults), marked by an impairment in reading, in which reasonable vision, intelligence, and most language functions other than reading remain intact.

apperceptive agnosia A form of visual agnosia in which a person cannot reliably name, match, or discriminate visually presented objects, despite adequate elementary visual function (visual fields, acuity, and color vision).

associative agnosia A form of visual agnosia in which a person cannot use the derived perceptual representation to access stored knowledge of the object's functions and associations but is able to copy and match the drawing even though unable to identify it.

Balint's syndrome Agnosic syndrome that results from large bilateral parietal lesions and is composed of three deficits: (i) paralysis of eye fixation with inability to look voluntarily into the peripheral visual field, (ii) optic ataxia, and (iii) disturbance of visual attention such that there is neglect of the peripheral field.

dorsal simultanagnosia An inability to detect more than one object at a time, with difficulty shifting attention from one object to another.

dorsal stream The stream of cortical visual projections from primary visual cortex to posterior parietal cortex, concerned primarily with the visual control of action and representation of spatial information.

inferotemporal cortex Inferior surface of the temporal lobe that is particularly important for object recognition.

Kluver-Bucy syndrome A group of impairments, including visual agnosia, resulting from bilateral damage to the temporal lobes.

optic aphasia A condition in which a person cannot name a visually presented object, despite being able to indicate the identity of the object through gesture and to sort the visual stimuli into categories.

prosopagnosia A form of visual agnosia in which a person cannot recognize faces, despite adequate elementary visual function (visual fields, acuity, and color vision).

ventral simultanagnosia A reduction in the ability to rapidly recognize multiple visual stimuli, such that recognition proceeds in a part-by-part fashion.

ventral stream The stream of cortical visual projections from primary visual cortex to the inferotemporal cortex, concerned primarily with representing the identity of stimuli by such characteristics as shape and color.

Visual agnosia is a disorder of recognition confined to the visual realm, in which a person cannot arrive at the meaning of some or all categories of previously known visual stimuli despite normal or near-normal visual perception and intact alertness, intelligence, and language. This article takes a multidisciplinary approach in discussing this impairment and considers clinical and neurological studies in humans as well as neurophysiological data in nonhuman primates.

Encyclopedia of the Human Brain Volume 1

Copyright 2002, Elsevier Science (USA).

All rights reserved.

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