Global temporal characteristics of English clear and conversational speech

Abstract

This study investigated the effect of hyperarticulated, intelligibility-enhancing clear speech on global temporal characteristics in paragraph-length utterances. The results of sentence-in-noise listening tests showed a consistent clear speech intelligibility gain across the utterances indicating that the talkers successfully maintained clear speech articulatory modifications throughout the paragraphs. We then explored temporal properties of the speech signal in terms of the percentage and variability of vocalic and consonantal intervals (following Ramus et al., 1999). Consonantal and vocalic intervals were lengthened equally in clear speech: %V remained stable across speaking styles. Moreover, coefficients of variation for both consonantal and vocalic intervals remained stable across clear and conversational speech, suggesting that global temporal properties remain rather stable in the two speaking styles. There was also evidence of an increase in the number of prosodic phrases and of vocalic and consonantal intervals for clear speech. Longer durations of consonantal segments in combination with insertion/strengthening of short consonantal segments that were dropped or coarticulated in conversational speech were reflected in an increased consonantal standard deviation in clear speech. Overall, these results suggest that increased intelligibility of clear speech may be attributed to prosodic structure enhancement (increased phrasing and enhanced segmentability) and stable global temporal properties.