Talker continuity and the use of rate information during phonetic perception.
Research has shown that speaking rate provides an important context for the perception of certain acoustic properties of speech. For example, syllable duration, which varies as a function of speaking rate, has been shown to influence the perception of voice onset time (VOT) for syllable-initial stop consonants. The purpose of the present experiments was to examine the influence of syllable duration when the initial portion of the syllable was produced by one talker and the remainder of the syllable was produced by a different talker. A short-duration and a long-duration /bi/-/pi/ continuum were synthesized with pitch and formant values appropriate to a female talker. When presented to listeners for identification, these stimuli demonstrated the typical effect of syllable duration on the voicing boundary: a shorter VOT boundary for the short stimuli than for the long stimuli. An /i/ vowel, synthesized with pitch and formant values appropriate to a male talker, was added to the end of each of the short tokens, producing a new hybrid continuum. Although the overall syllable duration of the hybrid stimuli equaled the original long stimuli, they produced a VOT boundary similar to that for the short stimuli. In a second experiment, two new /i/ vowels were synthesized. One had a pitch appropriate to a female talker with formant values appropriate to a male talker; the other had a pitch appropriate to a male talker and formants appropriate to a female talker. These vowels were used to create two new hybrid continua. In a third experiment, new hybrid continua were created by using more extreme male formant values. The results of both experiments demonstrated that the hybrid tokens with a change in pitch acted like the short stimuli, whereas the tokens with a change in formants acted like the long stimuli. A fourth experiment demonstrated that listeners could hear a change in talker with both sets of hybrid tokens. These results indicate that continuity of pitch but not formant structure appears to be the critical factor in the calculation of speaking rate within a syllable.