Dichotic listening and tactual mental rotation in females as a function of familial sinistrality and strength of handedness.

In this study the effects of familial sinistrality and strength of handedness on dichotic listening and tactual mental rotation were investigated. Nonfamilial left-handers were inferior to familial left-handers, particularly in right-ear performance. The decrement in right-ear performance is interpreted as indicative of a pathologically functioning left hemisphere in nonfamilial left-handers. The direction of ear asymmetry tends to be more predictable in strong left-handers than in weak left-handers, with nonfamilial strong left-handers showing a significant left-ear superiority and familial strong left-handers a nonsignificant right-ear superiority. In the tactual mental rotation task, the results suggest a preference of left-handers for a verbal encoding strategy, especially in the right hemisphere. This preferential strategy is particularly manifest in familial weak left-handers and nonfamilial strong left-handers. The results are discussed in terms of their implications for underlying patterns of cerebral organization in the left-handers.