An electromyographic examination of lip asymmetry during speech and non-speech oral movements in adults who stutter

Abstract

Past research investigating stuttering has cited atypical cerebral lateralization in adults who stutter (AWS) during speech production. The purpose of this study was to measure cerebral activation in AWS as indicated by lip asymmetry. The study included five AWS (mean age = 26 years of age) and five adults who do not stutter (AWNS) (mean age = 25 years of age). The tasks included single-word productions, single-sentence readings and lip pursings. The peak electromyographic (EMG) amplitude was determined for the left upper, right upper, left lower and right lower lip quadrants around the mouth. Overall, EMG amplitudes were higher for the lower lip than the upper lip. Based on examination of peak EMG amplitude, significant differences were found between speaker groups. For both speech and non-speech tasks, the highest EMG amplitude for the AWS and AWNS groups were on the left lower and right lower sides of the mouth, respectively. The AWNS group showed strong correlations in EMG activity across the four lip sites (r>0.97), indicating an overall synchronous lip activity during speech and non-speech tasks. In contrast, the AWS group showed a strong correlation (r=0.97) only for the left upper and left lower lips while the other lip pairings were not strongly correlated (r<0.738) indicating otherwise reduced synchronous lip activity. While the small sample size suggests caution, clear differences in the pattern of lip EMG activity demonstrated in the present study provides evidence of differences between AWS and AWNS in the cerebral activation governing lip movement. The greater left lip activity observed in AWS was indicative of greater right hemisphere cerebral activation while increased right lip activity was indicative of greater left hemisphere participation in AWNS. The results of the present study provided support for the hypotheses of reversed lateralization for speech and non-speech processing and reduced coordination of speech musculature in AWS.