ABSTRACT
Visual agnosia is a severe modality-specific deficit in the recognition of visually presented objects. It is recognition, rather than a naming deficit, since visual agnosic patients are unable to gesture the use or to show any recognition of the objects they fail to name. Typically, discussions of visual agnosia centre on Lissauer's (1890) distinction between apperceptive and associative agnosia. Lissauer argues that visual object recognition was composed of two primary independent stages; apperception, the process of constructing a perceptual representation from vision; and association, the process of mapping a perceptual representation onto stored knowledge of the object's functions and associations. Lissauer proposes that following brain damage, patients may be impaired in either the apperception or the association process, with both impairments giving rise to a deficit in visual object recognition. The distinction between apperceptive and associative agnosia introduced by Lissauer emphasizes a two-stage view of visual object recognition.
