In this investigation, the effects of context on the perception of voicing contrasts specified by voice-onset-time (VOT) in syllable-initial stop consonants were examined. In an earlier paper [J.L. Miller and L.E. Volaitis, Percept. Psychophys. 46, 505-512 (1989)], it was reported that the listener's adjustment for one contextual variable, speaking rate, was not confined to the region of the phonetic category boundary, but extended throughout the phonetic category. The current investigation examines whether this type of perceptual remapping also occurs for another contextual variable, the place of articulation of the syllable-initial consonant. In a preliminary experiment that involved acoustic measurement of natural speech, it was confirmed that as place of articulation moves from labial to velar, VOT increases, and it was established that this occurs across a range of speaking rates (syllable durations). In the main experiments, which focused on the voiceless category, it was found that this acoustic change was reflected in perception not only as a shift in the location of the voiced-voiceless category boundary, but also a change in both the specific range of stimuli identified as members of the voiceless category and the set of stimuli judged to be the best exemplars, or prototypes, of the category. These findings extend earlier research by showing that a change in place of articulation, like a change in speaking rate, systematically alters the internal perceptual structure of voicing categories.

When listeners process temporal properties of speech that convey information about the phonetic segments of the language, they do so in a rate-dependent manner. This is seen as a shift in the location of the phonetic category boundary along a temporal continuum toward longer values of the acoustic property in question, as speech is slowed. In a series of experiments, we found that the adjustment for rate is not confined to the region of the category boundary, but extends throughout the phonetic category. Specifically, a change in rate modified the range of stimuli identified as members of a phonetic category, as well as which stimuli were overtly judged to be good exemplars of the category. These findings suggest that the listener's adjustment for speaking rate entails a comprehensive perceptual remapping between acoustic signal and phonetic structure.Many of the acoustic properties of speech that specify the phonetic structure of an utterance-the sequences of consonants and vowels that define the lexical items of the language-are temporal in nature. When the property in question is short, it specifies one phonetic segment and when it is long, it specifies another.A potential complication arises, however, in that when speakers talk, they do not maintain a constant rate of speech (e.g., see Goldman-Eisler, 1968). Importantly, the change in rate involves not only a change in the number and duration of pauses within and between utterances, but a change in the acoustic structure of the speech signal itself. For example, Miller, Grosjean, and Lomanto (1984) found that speakers being interviewed on a radio talk show changed speaking rate frequently and substantially while answering questions. For 29 of the 30 speakers tested, the average duration of a syllable (measured over a stretch of pause-free speech) changed during the interview by as much as 100 msec, and for 20 of the 30 speakers, by as much as 300 msec.The critical issue for perception is how such alteration in speaking rate affects the temporal properties that specify phonetic structure. Take as an example the distinction in English between the voiced stop consonants (fbi, Id/, Ig/) and their voiceless counterparts (/p/, It!, IkI). One of the major properties distinguishing the two classes of con-

In the experiments reported in this paper we compared the effects of syllable-level and sentence-level speaking rate on phonetic perception. In an earlier set of experiments, we found that syllable-level rate influences the internal perceptual structure of phonetic categories [Miller and Volaitis, Percept. Psychophys. 46, 505-512 (1989); Volaitis and Miller, J. Acoust. Soc. Am. 92, 723-735 (1992)]. Specifically, a change in target-syllable rate altered the location of the stimuli judged to be the best category exemplars, as well as the width of this best-exemplar range. In the present investigation, it was asked whether sentence-level rate has the same influence. It was found that slowing sentence rate shifted the location of the best-exemplar range, but did not alter its width. These findings are discussed in terms of timing mechanisms that may operate during speech perception.

Many studies have shown that listeners process speech in a rate-dependent manner, altering the location of phonetic category boundaries in accord with the acoustic consequences of a change in rate during speech production. In a recent series of papers that focused on a voicing contrast, we reported that the perceptual adjustment for rate is not limited to the region of the category boundary, but extends to well within the category, producing a change in which stimuli are perceived to be the best category exemplars. In the current paper, we provide evidence for the generality of this effect by showing analogous results for a /b/––/w/ contrast, specified by transition duration. The implications of these findings for models of rate-dependent processing are discussed.

It is well known that when listeners identify consonants as voiced or voiceless on the basis of voice onset time (VOT), they do so in a rate-dependent manner: As rate of speech decreases such that overall syllable duration increases, the category boundary moves toward a longer VOT value. We have been examining whether this alteration in boundary location is accompanied by a change in the specific stimuli judged to be the best category exemplars. For our experiment we created two /bi/-/pi/ series with overall syllable durations of 125 and 325 ms, respectively. VOT varied from 10–120 ms for the 125-ms series and from 10–320 ms for the 325-ms series. We asked listeners to judge each syllable for its goodness as a member of the /p/ category, using a scale from 1–10; the higher the number, the better the exemplar. For each series, as VOT increased there was an initial increase in rating response, followed by a subsequent decline. Thus for both the short and long syllables, the /p/ category was perceived as having internal structure, with a limited range of stimuli serving as the best exemplars. However, the entire function for the longer syllables was shifted toward longer VOT values. That is, as syllable duration increased, so too did the VOT values of the stimuli judged to be the best category members. Moreover, in a subsequent control experiment we established that the shift in rating funtion was not due to range or frequency effects, but to the alteration in syllable duration, per se. These findings strongly suggest that the adjustment for speaking rate, whatever the underlying mechanism, involves a comprehensive modification in the mapping between acoustical signal and phonetic structure.