Interaction between vision and language in category-specific semantic impairment

A category-specific semantic disorder, selectively affecting living things and food and sparing inanimate objects, was observed in a patient (LA) who had made a partial recovery from herpes simplex encephalitis. This impairment was observed to have similar characteristics both with verbal and pictorial material, and a significant degree of consistency was observed between repeated presentations and across various modalities of administration of the same stimuli. In order to study the possible role of interactions between verbal-semantic and visual-semantic impairment, we constructed a test of “naming animals by definitions”, in which two sorts of definitions were contrasted: (1) those stressing visual perceptual features; and (2) those using verbal metaphorical expressions, or a description of the function accomplished by that animal for man, to allow identification. LA performed much better in the second than in the first condition. On the grounds of these results, the following hypotheses were advanced: (1) LA has a selectively impaired visual semantic system; (2) the categories selectively disrupted are those in which identification of a category member critically depends upon subtle visual discrimination; (3) disruption of the visual semantic system not only hampers picture identification, but also impairs object name definition, since this task can be greatly facilitated by evocation and consultation of visual-semantic information corresponding to the name of the object.