Dual functional brain asymmetry refers to the notion that in most individuals the left cerebral hemisphere is specialized for language functions, whereas the right cerebral hemisphere is more important than the left for the perception, construction, and recall of stimuli that are difficult to verbalize. In the last twenty years there have been scattered reports of sex differences in degree of hemispheric specialization. This review provides a critical framework within which two related topics are discussed: Do meaningful sex differences in (...) verbal or spatial cerebral lateralization exist? and, if so, Is the brain of one sex more symmetrically organized than the other? Data gathered on right-handed adults are examined from clinical studies of patients with unilateral brain lesions; from dichotic listening, tachistoscopic, and sensorimotor studies of functional asymmetries in non-brain-damaged subjects; from anatomical and electrophysiological investigations, as well as from the developmental literature. Retrospective and descriptive findings predominate over prospective and experimental methodologies. Nevertheless, there is an impressive accummulation of evidence suggesting that the male brain may be more asymmetrically organized than the female brain, both for verbal and nonverbal functions. These trends are rarely found in childhood but are often significant in the mature organism. (shrink)

The traditional verbal/nonverbal dichotomy is inadequate for completely describing cerebral lateralization. Musical functions are not necessarily mediated by the right hemisphere; evidence for a specialist left-hemisphere mechanism dedicated to the encoded speech signal is weakening, and the right hemisphere possesses considerable comprehensional powers. Right-hemisphere processing is often said to be characterized by holistic or gestalt apprehension, and face recognition may be mediated by this hemisphere partly because of these powers, partly because of the right hemisphere's involvement in emotional affect, and (...) possibly through the hypothesized existence of a specialist face processor or processors in the right. The latter hypothesis may, however, suffer the same fate as the one relating to a specialist encodedness processor for speech in the left. Verbal processing is largely the province of the left because of this hemisphere's possession of sequential, analytic, time-dependent mechanisms. Other distinctions are special cases of an analytic/holistic dichotomy. More fundamentally, however, the left hemisphere is characterized by its mediation of discriminations involving duration, temporal order, sequencing, and rhythm, at thesensory level, and especially at themotorlevel. Spatial aspects characterize the right, the mapping of exteroceptive body space, and the positions of fingers, limbs, and perhaps articulators, with respect to actual and target positions. Thus there is a continuum of function between the hemispheres, rather than a rigid dichotomy, the differences being quantitative rather than qualitative, of degree rather than of kind. (shrink)