Perceptual categorization in the cerebral hemispheres.

The suggestion of a functional hemispheric dissociation in performing perceptual categorization was examined in two tachistoscopic experiments with normal adults. Subjects were required to match physically identical or similar, but nonidentical, pictures of animals. The first experiment showed no hemispheric difference and indicated that both hemispheres could resort to two different types of categorization process as a function of the simultaneous or delayed mode of presentation of the stimuli. In the second experiment, the viewing conditions were manipulated so as to afford a reduced amount of stimulus energy, and a significant left-visual-field advantage was then obtained. The results are discussed with respect to models of information processing in the cerebral hemispheres, and in relation to impairments in object recognition following brain damage.