Inferring patterns of hemispheric specialization for individual subjects from laterality data: a two-task criterion.

Sixty-three subjects (31 dextrals and 32 sinistrals) were given two visual half-field laterality tasks (recognition of words and faces). Subjects were classified as having typical or atypical hemispheric specialization on the basis of the relative magnitude of their asymmetry scores on the two laterality tasks. Those subjects whose word asymmetry scores were larger than their face asymmetry scores (asymmetry scores computed as RVF-LVF for both tasks) were classified into Group Typical and those subjects whose word asymmetry scores were smaller than their face asymmetry scores were classified into Group Atypical. For both dextrals and sinistrals, the proportion of subjects classified into Groups Typical and Atypical was consistent with estimates of the incidence of typical and atypical hemispheric asymmetry patterns based on sodium amytal testing. These results support the hypothesis that the relative magnitude of asymmetry scores on left and right hemisphere specialized tasks index individual differences in patterns of hemispheric specialization.