The Hécaen-Zangwill legacy: hemispheric dominance examined.

The research of Henry Hécaen and Oliver Zangwill on patients with unilateral brain lesions in the later 1940s and early 1950s ushered in the modern era of investigation of hemispheric cerebral dominance. The field of inquiry expanded far beyond language and visual perception to encompass audition, somesthesis, motor performance, attentional processes, emotionality, and psychiatric disorders. The hundreds of studies dealing with the topic indicate that hemispheric dominance is not an all-or-none phenomenon and that, to some degree, it is an unstable phenomenon dependent upon bihemispheric factors. The basic cognitive processes that are preferentially mediated by each hemisphere and the factors that produce changes in performance still require adequate definition.