Clearly produced vowels exhibit longer duration and more extreme spectral properties than plain, conversational vowels. These features also characterize tense relative to lax vowels. This study explored the interaction of clear-speech and tensity effects by comparing clear and plain productions of three English tense-lax vowel pairs (/i-I/, /A-ˆ/, /u-U/ in /kVd/ words). Both temporal and spectral acoustic features were examined, including vowel duration, vowel-to-word duration ratio, formant frequency, and dynamic spectral characteristics. Results revealed that the tenseÀlax vowel difference was generally enhanced in clear relative to plain speech, but clear-speech modifications for tense and lax vowels showed a trade-off in the use of temporal and spectral cues. While plainto-clear vowel lengthening was greater for tense than lax vowels, clear-speech modifications in spectral change were larger for lax than tense vowels. Moreover, peripheral tense vowels showed more consistent clear-speech modifications in the temporal than spectral domain. Presumably, articulatory constraints limit the spectral variation of these extreme vowels, so clear-speech modifications resort to temporal features and reserve the primary spectral features for tensity contrasts. These findings suggest that clear-speech and tensity interactions involve compensatory modifications in different acoustic domains.

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Studies on acoustic and visual characteristics of English tense and lax vowels show consistent enhancement of tensity contrasts in clear speech. However, the degree to which listeners utilize these enhancements in speech perception remains unclear. The present study addresses this issue by testing speech style effects on tense and lax vowel perception by 23 native English and 30 non-native Mandarin-Chinese listeners in audio-only (AO), audio-visual (AV), and visual-only (VO) stimulus modes. English and Chinese listeners showed similar relative differences in performance by mode (VO < AO < AV) and style (plain < clear). However, the two groups differed in the nature of the interaction between tensity, style, and stimulus mode. English listeners showed advantages for clear speech for both tense and lax vowels in all but VO stimuli, whereas Chinese listeners showed a clear speech advantage only for tense vowels, while clear lax vowels showed no improvement in AO and reduced accuracy in AV and VO. While temporal and spectral acoustic cues may coordinate to preserve or improve tense-lax category identity in clear speech, non-native listeners may not be attending to both dimensions. Further, Chinese listeners' greater reliance on visual information may account for their less accurate lax vowel identification.

This study aims to characterize distinctive acoustic features of Mandarin tones based on a corpus of 1025 monosyllabic words produced by 21 native Mandarin speakers. For each tone, 22 acoustic cues were extracted. Besides standard F0, duration, and intensity measures, further cues were determined by fitting two mathematical functions to the pitch contours. The first function is a parabola, which gives three parameters: a mean F0, an F0 slope, and an F0 second derivative. The second is a broken-line function, which models the contour as a continuous curve consisting of two lines with a single breakpoint. Cohen's d, sparse Principal Component Analysis, and other statistical measures are used to identify which of the cues, and which combinations of the cues, are important for distinguishing each tone from each other among all the speakers. Although the specific cues that best characterize the tone contours depend on the particular tone and the statistical measure used, this paper shows that the three cues obtained by fitting a parabola to the tone contour are broadly effective. This research suggests using these three cues as a canonical choice for defining tone characteristics.