The effects of phonetic complexity on vowel formant variability in apraxia of speech

Apraxia of speech (AOS) results from left anterior brain damage and is characterized by reduced intelligibility, inconsistent distortion errors and dysprosody. Few studies have systematically investigated speech errors in AOS, possibly due to the high individual variability in production. Analysis of contextual effects may help to describe the sources of variability and elucidate the underlying deficit in apraxia. The purpose of this study was to determine whether consonant complexity affects vowel formants in AOS. Participants repeated 36 consonant-vowel-consonant (CVC) syllables with manipulated consonantal complexity. Each syllable contained one of three vowels: /i/, /a/ or /u/. Acoustic analysis of vowel production by speakers with apraxia revealed formant frequencies within a normal range. Vowel formants in AOS were less stable with greater variability for /u/. Systemic effects of complexity on vowel formant variability in AOS were not observed. The lack of complexity effects suggests that speakers with AOS have disrupted access to syllabic encoding. Further investigation of complexity effects on vowel duration and vowel production variability in consonant-vowel-consonant-vowel (CVCV) contexts is warranted.