Factor analysis and the cerebral hemispheres: pilot study and parietal functions.

Although research on lateral differences has proliferated, attempts to specify fundamental dichotomies of hemispheric processing have yielded less than satisfactory results. The factor analysis of behavioral asymmetries can provide a different approach by helping to identify common functions underlying disparate tasks. It can also provide information on individual differences and interrelationships among functions. Here, the viability of the approach is demonstrated with a small pilot study (N = 29), and with two larger experiments (N = 70 and N = 60) that stress parietal lobe function. Seven lateralized functions were identified: auditory lexical, spatial attentive, spatial positional, spatial quantitative, tactile figural, visual emotional and visual lexical. A range of positive, negative and null correlations was found between functions, contrary to lateralization strength, hemisphericity, and independence models of individual differences in lateralization. However, a pattern of intercorrelations was observed among functions believed to be localized to the perisylvian region (Brodmann areas 22 and 39), which is consistent with the neurodevelopment theory of Geschwind and Galaburda (Cerebral Lateralization Biological Mechanisms, Associations and Pathology, The MIT Press, Cambridge, MA, 1987).