Second-formant locus patterns in dysarthric speech

Abstract

Second-formant (F2) locus equations represent a linear relationship between F2 measured at the vowel onset following stop release and F2 measured at the vowel midpoint in a consonant-vowel (CV) sequence. Prior research has used the slope and intercept of locus equations as indices to coarticulation degree and the consonant’s place of articulation. This presentation addresses coarticulation degree and place of articulation contrasts in dysarthric speech, by comparing locus equation measures for speakers with cerebral palsy and control speakers. Locus equation data are extracted from the Universal Access Speech (Kim et al. 2008). The data consist of CV sequences with labial, alveolar, velar stops produced in the context of various vowels that differ in backness and thus in F2. Results show that for alveolars and labials, slopes are less steep and intercepts are higher in dysarthric speech compared to normal speech, indicating a reduced degree of coarticulation in CV transitions, while for front and back velars, the opposite pattern is observed. In addition, a second-order locus equation analysis shows a reduced separation especially between alveolars and front velars in dysarthric speech. Results will be discussed in relation to the horizontal tongue body positions in CV transitions in dysarthric speech.