Mouth asymmetry during spontaneous speech

A high proportion of normal subjects have speech expression controlled predominantly by the left hemisphere. Since the left hemisphere also has stronger control of the right side of the lower face, it might be expected that normal subjects would show a right-sided asymmetry in mouth opening during speech. This hypothesis was tested by measuring lip opening in 196 subjects. Of these, 150 (76%) showed greater right-side opening. This tendency was found for males, females, left- and right-handers in four experiments using two different techniques. Mouth asymmetry during speech may provide an indication of which hemisphere is dominant for expressive speech.