Lateral Differences in Gesture
Two lines of thought converge to suggest that some insights into the brain mechanisms underlying speech may be gained from a study of gestures. One is the idea that verbal and nonverbal systems do not constitute separate communication modes, specialized in the transmission of rational and emotional information, respectively; human communication could better be conceived as a multichannel process where meaning is represented either by words or gestures ( A. Kendon , Ch. 1). The other is a modification in the conception of hemispheric specialization, which substitutes for the verbal/nonverbal dichotomy more "functional" dichotomies such as serial/parallel and analytic/holistic. In this perspective, the left-hemispheric advantage in verbal tasks arises from a specialization of that hemisphere in sequential, analytical, or high-resolution processes. In both cases, a shared property of language and gestures is stressed: both are able to convey meaning, and both do it by way of motor activity (articulation or gesticulation). Thus, researchers have begun to look for common cerebral mechanisms, and data have been collected in two areas: in the lateral differences in hand movements of normal subjects and in the manual activity of unilaterally brain-damaged subjects.
However, the relevance of these studies for the knowledge of control mechanisms underlying speech and gestures remains unclear. Different interpretations of the data may be offered. The studies reviewed here show that evidence for a common cerebral basis in the control of oral and manual movements is still lacking and that more precise models describing both the specificity and the commonalities of language and gestures are needed.