This investigation examined the timing relationships of EMG activity underlying vowel production in two normal individuals and two individuals with marked-to-severe apraxia of speech of approximately 2 1/2 years duration. The timing of lip muscle activity was investigated in monosyllabic words embedded in phrases. Specifically, the onset and offset of EMG activity of lip muscles used for production of /u/ in the monosyllables were examined. The results revealed that the relative amounts of time devoted to onset and offset of EMG activity for lip rounding are disorganized in apraxia of speech. The findings suggest that termination of EMG activity may be at least as disturbed as the initiation of EMG activity in apraxia of speech.
