Right brain, left brain; left face, right face: hemisphericity and the expression of facial emotion.

Research on the asymmetry of facial expressions is reviewed in terms of neuroanatomy, qualitative and quantitative measures of asymmetrical expression, method of expression elicitation (spontaneous, posed, imagery-based), type of expression (happy, sad, etc.), and expression rating procedures. Neuroanatomical evidence indicated that contralateral control of facial musculature exists only for the lower face and that different motor pathways are responsible for spontaneous versus posed expressions. Empirical research on the differential assignment of qualitative trait attributes to facial regions was judged to be meagre and data on quantitative differences in the asymmetry of facial expressions was inconclusive because of the wide variability in methodology across past investigations. Specific suggestions for future investigations in this area are offered and alternative conceptualizations of hemisphericity and facial asymmetry proposed.