Fractionation of Spatial Cognition following Focal and Diffuse Brain Damage

Abstract

Visuospatial dysfunction denotes a constellation of perceptual and constructional deficits in which the ability to organize visual features into perceptual wholes is lost or impaired. Despite the high incidence of visuospatial deficits following brain damage, there have been relatively few neuropsychological investigations of visuospatial dysfunction relative to the large number of studies of aphasia. Several reasons may underlie this disparity. While the structure of language is discrete and readily observable (Luria, 1966), the structure of visuospatial cognition is much more elusive. Visuospatial structure, unlike linguistic structure, does not contain temporally discrete entities, such as phonemes and words, but must be inferred from perceptual judgments and visuospatial constructions. This diffuse quality hinders the development of a grammar of visuospatial thinking (Chomsky, 1965; Fillmore, 1971). Additionally, specific brain lesions often interrupt aspects of linguistic processes in well-defined ways, enabling the development of reliable taxonomies of aphasias (Geschwind, 1970; Goodglass & Kaplan, 1972). In contrast, when visuospatial abilities are disrupted by brain damage, the nature of the impairment is difficult to characterize in a precise manner. Not surprisingly, one rarely refers to visuospatial syndromes resulting from specific brain lesions; instead, difficulties on visuospatial tasks tend to be amalgamated into one category and referred to as “visuospatial dysfunction,” “constructional apraxia,” or “constructional difficulties.”