Effects of Clear Speech and Linguistic Experience on Acoustic Characteristics of Vowel Production

The present study investigated the hypothesis that later and/or early learners of English as a second language may exhibit an exaggerated or restricted degree of change in their production performance between clear and conversational speech styles for certain acoustic cues. Monolingual English talkers (MO), early Spanish-English bilinguals (EB) and late Spanish-English bilinguals (LB) were recorded using both clear and conversational speaking styles. The stimuli consisted of six target vowels /i, I, e, E, ae/ and /a/, embedded in /bVd/ context. All recorded target-word stimuli were isolated into words. Vowel duration was computed, and fundamental frequency (F0), and formant frequency values (F1-F4) were measured at 20%, 50%, and 80% of the vowel duration. Data from the MO and EB talkers indicates that these two groups are very similar in that they emphasize duration differences in clear speech, have similar spacing of vowels (static & dynamic properties), and have similar frequency changes in clear speech. Data from the LB talkers indicates that this group failed to emphasize differences in clear speech, particularly duration differences. In addition, the high-mid front vowels (/i, I, e/ and /E/) were found to be very poorly separated in the F1-F2 space for the LB talkers. In support of the hypothesis, the data showed that LB talkers exhibited a restricted degree of change in their production performance between clear and conversational speech styles for duration, as compared to monolingual talkers. Data analyzed for the EB talkers do not reveal systematic reductions in the degree of change in their production performance between clear and conversational speech styles, as compared to monolingual talkers