The ability of native and non-native speakers to enhance intelligibility of target vowels by speaking clearly was compared across three talker groups: monolingual English speakers and native Spanish speakers with either an earlier or a later age of immersion in an English-speaking environment. Talkers produced the target syllables "bead, bid, bayed, bed, bad" and "bod" in 'conversational' and clear speech styles. The stimuli were presented to native English-speaking listeners in multi-talker babble with signal-to-noise ratios of Ϫ8 dB for the monolingual and early learners and Ϫ4 dB for the later learners. The monolinguals and early learners of English showed a similar average clear speech benefit, and the early learners showed equal or greater intelligibility than monolinguals for most target vowels. The 4-dB difference in signal-to-noise ratio yielded approximately equal average intelligibility for the monolinguals and later learners. The average clear speech benefit was smallest for the later learners, and a significant clear speech decrement was obtained for the target syllable "bid." These results suggest that later learners of English as a second language may be less able than monolinguals to accommodate listeners in noisy environments, due to a reduced ability to improve intelligibility by speaking more clearly.

No abstract

Vowel-inherent spectral change (VISC) refers to vowel-intrinsic formant movement across a vowel steady state. VISC has been shown to (1) be consistent across talkers within a given dialect, (2) vary regularly across vowels within a dialect, (3) vary regularly across dialects, and (4) be necessary for peak vowel-identification accuracy. Hence, VISC has become accepted as a phonetic feature of monophthong vowels of North American English. VISC is typically portrayed using averages across tokens and talkers, highlighting regularity but potentially masking individual differences. To understand vowel production by second-language learners, we were particularly interested in such individual variation. In analyzing individual differences for neighboring target vowels, we found no single time point at which all sets of target vowel tokens were well distinguished from one another. However, looking across three time points, all native-speaker vowel sets were well distinguished from each possible neighbor set at some time point. Thus, VISC can be seen as the steps in a sort of dance, as each vowel moves to avoid overlapping with another, ultimately causing overlap with another and then more movement. This perspective is compatible with models of efficient coding and stochastic and/or exemplar based models of speech production and perception. [NIH-NIDCD #1R03DC005561-01A1.]

The degree to which vowel duration and time-varying spectral change cues are used in American English vowel identification was investigated for three groups of listeners: (1) monolingual American English listeners; (2) proficient Spanish-English bilinguals; and (3) less proficient Spanish-English bilinguals. Digital manipulation and high-fidelity synthesis procedures (STRAIGHT) were used to create six versions of six target items (bead, bid, bayed, bed, bad, and bod). These consisted of the unaltered whole word and five versions of the isolated vowel: (1) natural vowel—unaltered; (2) synthetic vowel with no cue alteration; (3) synthetic vowel with neutral duration; (4) synthetic vowel with flattened formants; and (5) synthetic vowel with neutral duration and flattened formants. Isolated-vowel stimuli were presented to listeners for identification in two 120-trial blocks, followed by 48 whole-word stimuli. Significant between-group differences in percent-correct performance and a significant group by listening condition interaction were found, suggesting that cue weighting may vary across groups and that some bilinguals’ phoneme representations may be less robust than those of monolinguals. Analysis of confusion matrix data will be used to further explore these hypotheses by examining patterns of confusions across group and condition and extent of individual differences across subjects within a group. [Work supported by NIH-NIDCD 1R03DC005561-01A1.]

The present study investigates the hypothesis that bilinguals may produce a smaller intelligibility benefit than monolinguals when asked to speak clearly. Three groups of talkers were recorded: 13 monolingual native English speakers, 22 early Spanish-English bilinguals, with an age of onset of learning English (AOL) of 12 or earlier, and 14 later Spanish-English bilinguals, with an AOL of 15 or later. Talkers produced the target words ‘‘bead, bid, bayed, bed, bad’’ and ‘‘bod’’ in both clear and conversational speech styles. Two repetitions of each target word were mixed with noise and presented to monolingual English-speaking listeners in a six-alternative forced-choice task across two days of testing. Stimuli were also presented in quiet on two subsequent days of testing. In preliminary data from 13 listeners, the early bilinguals were slightly more intelligible in noise than the monolingual talkers, with both groups showing a similar degree of clear speech benefit. Later bilinguals were less intelligible overall and showed a much smaller clear speech benefit in noise. These data suggest that later bilinguals, but not early bilinguals, may experience a disadvantage when speaking in noise due to a reduced ability to improve intelligibility by speaking more clearly [Work supported by NIH].