Lip EMG activity during vowel production in apraxia of speech: phrase context and word length effects

This investigation examined the timing relationships of EMG activity underlying vowel production in 2 normal individuals and in 2 individuals with marked-to-severe apraxia of speech of approximately two-and-one-half years duration. The timing of lip muscle activity was investigated in monosyllabic words embedded in phrases and in syllable word stems as a function of changes in word length. Specifically, the onset and offset of EMG activity of lip muscles used for production of /u/ in the monosyllables and word stems 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. Word length appeared to affect the timing of the onset of muscle activity for both the normal speakers and the speakers with apraxia of speech. Word length also influenced the offset of muscle activity, but its effect was less systematic for the speakers with 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.