| Summary: | 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.
|
|---|
