Hemispheric asymmetry in face perception tasks of different cognitive requirement.

Three laterality experiments using tasks of different cognitive requirement were performed in order to determine the stage at which hemispheric differences in face perception arise. All experiments employed the same set of faces and a vocal reaction time paradigm. In experiment 1, subjects were required to discriminate male from female faces and no hemispheric asymmetries were found. In experiment 2, subjects were required to decide whether or not faces were of famous or unknown people and a right hemisphere advantage was found. Finally, in experiment 3 subjects were required to verbally identify the famous faces and no hemispheric differences were found. The results suggest that a right hemisphere superiority exists for the comparison of stimulus faces with an internal representation. Contrary to expectation, face naming does not result in a selective left hemisphere involvement.