A twin study of individual differences in perceptual asymmetry.

Individual differences in perceptual asymmetry have been associated with individual differences in cognitive abilities, personality characteristics, and psychiatric symptoms, for which between-person variation appears to be genetically influenced. Perceptual asymmetry scores are also associated with direction of handedness, for which between-person variation does not appear to be genetically influenced. To assess whether between-person variation of perceptual asymmetry scores is genetically influenced, we examined asymmetry on a freevision task of face processing, the Chimeric Faces Task (CFT), in a sample of 31 monozygotic (MZ) and 20 same-sex dizygotic (DZ) twin pairs. MZ and DZ within twin-pair resemblances were compared to assess genetic and familial influences on asymmetric hemispheric function. We found that twins within a pair were no more likely to resemble each other than were unrelated individuals. The results suggest that the between-person variation in CFT perceptual asymmetry is not influenced by genes or shared environment.