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The effect of noise on segmental and prosodic timing in speech production Bradford, Louise


The present investigation examined the effects of noise on prosodic and segmental timing in speech production, focusing on preboundary lengthening, pausing, speaking rate and trends in segmental duration. Preboundary lengthening was examined using normalized duration measurements. Four subjects participated in this study. Each read syntactically ambiguous sentences to a listener under conditions of quiet and multitalker babble. These sentences were then labeled by listeners according to a seven-point scale of perceived boundary strength (or break index). Each break index corresponded to a level of prosodic phrasing proposed in the literature. In general, speakers were highly individualistic in the ways they altered the segmental components of speech in noise. Three of four subjects decreased their rates of speaking in noise to varying degrees. The greatest changes in segmental durations were observed in vowels and sonorants. Changes in consonant durations were more subject specific. Both the distribution and durations of pauses were characterized by a large degree of intersubject variability. The number of pauses tended to increase with increasing perceptual boundary strength, and pauses at the larger phrase boundaries were significantly longer than those at lower levels of phrasing. Preboundary lengthening was found to increase rapidly across three lower levels of phrasing, while almost no differences were observed between the two highest levels of phrasing across both speaking conditions. This suggests that preboundary lengthening is an important perceptual cue to the lower levels of phrasing, which are marked by few other phonetic cues. The effect of noise on overall timing relationships between prosodic constituents was minimal. The degree of preboundary lengthening remained relatively constant across speaking conditions for all four subjects participating in the experiment. It is proposed that speakers try to maintain prosodic timing relationships in order to preserve speech intelligibility in noise.

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