Complementarity of cerebral function among individuals with atypical laterality profiles

Recent work has revealed that lateral preferences other than handedness are important correlates of the cerebral lateralization of higher functions. T his paper investigates the nature of the complementarity of the processing of the verbal aspect of language and that of its prosodic dimension in indi viduals with unusual combinations of lateral preferences. We administered b oth linguistic and prosodic dichotic-listening tasks and laterality prefere nce questionnaires to 47 individuals. Although most individuals exhibited t he typical left-hemisphere-verbal and right-hemisphere-prosodic effects, fo otedness was the only preference that differentiated between different curr ent models of complementarity. Correlations between scores on the prosodic and linguistic tasks were positive, and significantly higher for right-foot ed participants than for left-footed participants. Complementarity of cereb ral function (the notion that each hemisphere subserves complementary funct ions) is the prototypical pattern of brain organization. The idea that the right hemisphere is specialized to perform nonverbal processing because the left-hemisphere preferentially deals with language processing is referred to as 'causal complementarity' (Bryden, Hecaen, & DeAgostini, 1983), and un derlies some models of the development of cerebral laterality (see Corballi s & Morgan, 1978; MacNeilage, 1991). Bryden articulated two alternative sce narios in addition to causal complementarity (Bryden, 1990; Bulman-Fleming & Bryden, 1998). His "statistical-complementarity" model is one in which th e processes by which lateralization of various functions occur are independ ent of one other, and his "bias" model posits underlying anatomical asymmet ries as heavily influencing behavioral asymmetries. Each of these models pr edicts a different correlation between tasks tapping right-and left-hemisph ere functions. The causal model predicts a negative correlation, the statis tical model predicts a lack of correlation, and the bias model predicts a p ositive correlation. We report here the testing of 47 individuals selective ly recruited because of their atypical laterality phenotypes, because recen t work has suggested the importance of preferences other than writing hand to patterns of hemispheric specialization (Elias & Bryden, 1998; Elias, Bry den, & Bulman-Fleming, 1998). (C) 1999 Academic Press.