An acoustic study of vowels and coarticulation as a function of utterance type: A case of acquired apraxia of speech

Abstract

This case study examines vowel production and coarticulation patterns in AOS as a function of utterance type. A female speaker with AOS, and a sex-matched control participant repeated target vowels in three conditions: isolated word, statement frames and question frames. The first two formant frequencies (F1 and F2) of the target vowels were measured at their onset and temporal midpoints. The vowel spaces of both speakers were examined using a two-dimensional vowel chart; temporal midpoint formant frequency values of the first formant (F1) were plotted against the difference between F2 and F1 (F2–F1) as a representation of the constricted versus open (F1) and fronted versus backed (F2–F1) quality of vowels. The speaker with AOS produced vowels that deviated to a posterior/backed distribution within the vowel space. Coarticulation patterns were also examined using F2 locus equations. The speaker with AOS exhibited reduced coarticulation patterns in all three conditions, when compared to the control speaker. Furthermore, these effects were amplified with increasing motoric complexity. The data elucidate the nature of the compromised speech control system in a speaker with AOS.