Different lip asymmetry in adults who stutter: electromyographic evidence during speech and non-speech.

The present study examined whether abnormal cerebral control was evident in the lip movements of adult stutterers (AS) compared to non-stutterers (ANS), as demonstrated during speech and non-speech tasks. Electromyographic (EMG) activity during production of words with initial /f/ and /p/ phonemes, single-sentence production and lip pursing were measured. Differences between AS and ANS were evident in all tasks. For AS, the highest EMG amplitude was in the region of the left lower lip, which is indicative of greater right hemisphere participation. However, in ANS the right lower lip displayed the highest EMG amplitude, suggesting greater left hemisphere participation. Further, AS showed greater asynchronous lip activity than ANS for all tasks. These results support the hypotheses of reversed lateralization for speech and non-speech processing and reduced coordination of speech musculature in AS.