Preserved Visual Imagery and Categorization in a Case of Associative Visual Agnosia

Abstract

A patient with associative visual agnosia secondary to a penetrating bitemporooccipital lesion remained able to draw complex objects from memory but could not subsequently recognize his sketches. His retained ability to copy and draw briefly exposed objects indicates that this is not a problem of visual perception. On tasks of categorization, mental imagery, drawing, and object decision, he demonstrates many instances of preserved visual semantic memories and imagery despite a sense of unfamiliarity with the visual stimuli. We infer a preserved ability to derive internal visual images from semantic memory. Cues may help him visualize the named object, which then serves as a model for comparison with the actual stimulus. However, his adequate visual perception and mental visual imagery, even when assisted by cues, are still insufficient to correct fully his difficulty in recognizing objects. Unique to his case is an inability to match the representation of stimulus objects with his intact internal image of the same object. Deficient lateral inhibition between neural representations of similar objects may be responsible.

Preserved visual imagery in visual form agnosia

“…showed excellent visual imagery. A patient with a similar dissociation between perceptual report and visual imagery has been described by Jankowiak et aL [37]. This patient (M.D.)…”

Absence of perceptual segmentation in image generation by normals

“…The coexistence of Absence of perceptual segmentation in image generation by normals 1 the impaired perceptual segmentation and the intact image generation in CK suggests that perceptual segmentation may not be involved in the generation of visual mental images. A similar case was reported by Jankowiak, Kinsbourne, Shalev, and Bachman (1992).…”

“…If the results cited above of Behrmann et al (1994) and Jankowiak et al (1992) with braindamaged patients mean that perceptual segmentation is generally not conducted in image generation, then it is predicted that, in the transfer-appropriate processing paradigm, an image generation task will not transfer to a perceptual segmentation task in normals. It is also predicted that an image generation task will transfer to a semantic processing task, because most researchers agree that vision and image generation share some higher mental processes (see Finke, 1989;Kosslyn, 1994;Kosslyn & Ochsner, 1994;Roland & Gulyas, 1994).…”

What does visual agnosia tell us about perceptual organization and its relationship to object perception?

“…The problem applies equally to the recognition of two-and three-dimensional stimuli and to black and white and chromatic displays although, in some cases, the presence of depth, color, and surface cues may be of some assistance to the patients in segmenting the display (Chainay & Humphreys, 2001;Farah, 1990;Humphrey, Goodale, Jakobson, & Servos, 1994;Jankowiak, Kinsbourne, Shalev, & Bachman, 1992).…”