Effects of length and linguistic complexity on temporal acoustic measures in apraxia of speech

The purpose of this study was to examine the effects of varying length and linguistic utterance types on temporal acoustic characteristics of the imitative speech of apraxic speakers. Vowel duration and two between-word segment durations were examined during the production of three response types: words, word-strings, and sentences. Three length conditions were studied in words, two length conditions for word-strings, and three length conditions for sentences, yielding eight experimental conditions. Apraxic speakers exhibited significantly longer vowel and between-word segment durations than control speakers in all conditions. Apraxic speakers consistently produced longer vowel and between-word segment durations in sentence contexts than in word contexts. Further, intrasubject and intersubject variability for between-word segment durations were substantially greater for the apraxic speakers in sentences compared to word conditions, whereas control speakers exhibited greater homogeneity in sentence production. The differences in duration and variability in sentence production versus word or word-string production imply different mechanisms for executing motor programs for varying linguistic stimuli.