The Asymmetry of Facial Actions Is Inconsistent with Models of Hemispheric Specialization

Abstract

Recent reports have suggested that asymmetries in facial expressions result from cerebral hemispheric specialization. This chapter evaluates the theoretical models on whether emotional or nonemotional neural processes are involved, and whether specialization of the right, the left, or both hemispheres underlies asymmetry. The results indicate that factors producing asymmetry in deliberate movements are not related directly to positive emotional processes involving smiling, nor to processes giving rise to negative, reflex-like startle reactions. It is also shown that asymmetries of certain individual deliberate actions are lateralized, implying that the subjects have in common some functional asymmetry related to differential use of the hemispheres or some structural, anatomical asymmetry, or both asymmetries. The background for the preceding study is the conviction that the phenomenon of asymmetry in facial muscular actions might reflect important aspects of neural action or other factors. Its main point is that no extant theory of a single process involving hemispheric specialization could explain the pattern of results in the study.