Sex differences in oral asymmetries during wordrepetition.

During speech production the right side of the mouth is opened to a larger degree in most people. This facial asymmetry is thought to be related to a left hemisphere dominance in language processing and/or motor programming. We investigated asymmetrical lip separations during discrete or serial word productions in right handed persons. The results revealed a right sided lip separation bias in both genders during discrete word production in which the words had to be uttered once. As soon as the words had to be produced continuously, however, a clear sex difference appeared with males having the usual right bias but females now showing no clear asymmetry, with a tendency for larger lip separations on the left side. These results suggest the existence of two separate neural systems from which one controls the discrete task and which is left hemisphere dominant in both genders. The other is probably involved in serial word productions and shows a sex difference with regard to its asymmetry pattern.