ABSTRACT
The search for principles that could uniquely characterize the processing differences underlying hemispheric functions has, for several decades, been the main focus of investigation in the study of cerebral lateralization. It has led to the identification of dichotomous dimensions distinguishing the respective competences of the hemispheres, and specifically to three broad categories along which the two hemispheres are assumed to divide their particular capacities. One is concerned with the nature of the information that each hemisphere would be specialized for dealing with, and it is best illustrated by the verbal/visuospatial dichotomy. Another has considered the nature of the operations, or the cognitive style, predominantly mediated by each hemisphere, and it is exemplified by the distinction between analytic and holistic modes of processing. The third broad category is concerned with the nature of the representations of information within each hemisphere, and it has led to the suggestion of an unequal ability of the hemispheres to operate on different spatial frequency contents of the information. Each of these dichotomies focuses on one aspect of the functional properties of the cerebral hemispheres and each has found some form of justification in the findings of various experimental studies conducted on normal and neurological populations. For instance, when dealing with brain-damaged patients in a clinical context, the validity of the verbal/visuospatial dichotomy is almost immediately evident, and it offers a highly reliable basis for telling apart left and right hemisphere damaged patients. Similarly, the analytic/holistic dichotomy can discriminate reasonably well between left and right posterior patients in visual perceptual tasks, as can the spatial-frequency hypothesis when tested with low-pass and high-pass stimuli.
