Asymmetries in mouth opening during word generation in male stuttering and non-stuttering participants

We examined lateral asymmetries in mouth opening in right-handed male stuttering (N = 11) and non-stuttering (N = 14) participants. Lateral asymmetries in mouth opening were video-recorded and analysed in participants while they generated words beginning with the bilabial phones /b, p, m/. Non-stuttering participants showed an expected preference for right mouth opening during the task, whereas a group of stuttering participants who were matched for sex and age produced a left or bilateral pattern of mouth opening. Analysis of variance revealed the difference between the groups to be significant (p < .001). However, there was more variability in the lateral mouth asymmetries in the stuttering participants. We interpret this finding as adding some support for the hypothesis that aberrant hemispheric control for speech is involved in stuttering. Asymmetric mouth openings appear to have no direct linguistic function, and we discuss the possible implications of the phenomenon for models of speech planning and programming.