A deficit in perceptual matching in the left hemisphere of a callosotomy patient

Decades of research have demonstrated dramatic differences between the hemi spheres of the brain. While the most obvious asymmetries are in the areas o f language and motor control, the visuospatial abilities of the left hemisp here are also known to differ from those of the right hemisphere. This hemi spheric difference has been demonstrated empirically but its basis is thus far unclear. In this paper, we investigate the hypothesis that the left hem isphere is capable of sophisticated Visual processing, but represents spati al information relatively crudely compared to the right hemisphere. The imp lication of this hypothesis is that pattern recognition is a function of bo th hemispheres but the right hemisphere is further specialized for processi ng spatial information. In a series of seven experiments we examined percep tual matching of mirror-reversed stimuli by the divided cerebral hemisphere s of a callosotomy patient. In each experiment the left hemisphere's perfor mance was impaired relative to the right hemisphere. This finding was indep endent of stimulus type, response bias and stimulus duration. These results are consistent with the idea that visual processing in the left hemisphere is directed towards pattern recognition at the expense of spatial informat ion. (C) 1999 Elsevier Science Ltd. All rights reserved.