The Two Sides of Perception

Anatomically, the central nervous system looks remarkably symmetrical--from therelatively simple structures of the spinal cord to the extensively convoluted folds of the cerebralhemispheres. At the functional level, however, there are striking differences between the left andright hemispheres. Although popular writings attribute language abilities to the left hemisphere andspatial abilities to the right, differences in hemispheric function appear to be more subtle.According to Ivry and Robertson, asymmetries over a wide range of perceptual tasks reflect adifference in strength rather than kind, with both hemispheres contributing to the performance ofcomplex tasks, whether linguistic or spatial.

After an historical introduction,the authors offer a cognitive neuroscience perspective on hemispheric specialization in perception.They propose that the two hemispheres differ in how they filter task-relevant sensory information.Building on the idea that the hemispheres construct asymmetric representations, the hypothesisprovides a novel account of many laterality effects. A notable feature of the authors' work is theirattempt to incorporate hemispheric specialization in vision, audition, music, and language within acommon framework. In support of their theory, they review studies involving both healthy andneurologically impaired individuals. They also provide a series of simulations to demonstrate theunderlying computational principles of their theory. Their work thus describes both the cognitiveand neurological architecture of hemispheric asymmetries in perception.