Speaking rate affects perception of good exemplars of a phonetic category

Abstract

An important property distinguishing syllable‐initial stop consonant, /b/, from semivowel, /w/, is the duration of the initial formant transitions: Relatively short transitions specify /b/, whereas longer transitions specify /w/. We reported earlier [J. L. Miller and A.M. Liberman, J. Acoust. Soc. Am. 68, S31 (1978)] that the transition duration at the /b/‐/w/ phonetic boundary is not absolute. Instead, as the syllables become longer, an increasingly longer transition is required to hear /w/. We proposed that the alteration in syllable duration specifies a change in speaking rate, and that the shift in boundary location reflects the listener's adjustment to that change. In the present experiment we asked whether the effect of syllable duration is limited to stimuli near the /b/‐/w/ boundary or extends to the processing of good exemplars of the phonetic categories. A selective adaptation procedure was used to assess perception of two series of syllables that varied in transition duration and ranged from /bæ/ to /wæ/; the series differed from each other only in overall syllable duration. On the basis of the adaptation data we were able to infer that both the location of the /b/‐/w/ boundary and the location of the prototypical or “best” /wæ/ were located at a longer transition duration for the long syllables, as compared to the short syllables. These data indicate that a change in speaking rate affects the way in which acoustic information is mapped onto phonetic categories, in terms of both the boundary between categories and the best exemplars of a given category. [Supported by NIH.]