On the nature of the listener's adjustment for speaking rate during phonetic perception

Abstract

It is now well established that speaking rate exerts a systematic influence on a variety of temporal properties that convey segmental information, and that the listener appropriately adjusts for speaking rate when using these properties to make phonetic decisions. The concern of the present investigation is the nature of the rate information to which the listener adjusts, whether physical rate or perceived rate. Our experiments focused on the distinction between stop consonant and semivowel in the syllables /ba/ and /wa/. We have reported previously that when listeners use transition duration to identify syllables as /ba/ or /wa/, they do so in relation to the overall duration of the syllables: as the syllables become longer and are perceived as having been produced at a slower rate of speech, a longer transition is required to convert /ba/ to /wa/. In the experiments we now report, we investigated whether the adjustment for rate is based on the actual physical rate of the syllables (i.e., syllable duration) or on their perceived rate. We used a contrast procedure to alter the perceived rate of the syllables while keeping physical rate constant, and then assessed the effect of this manipulation on the identification of the syllables as /ba/ or /wa/. We found that changes in perceived rate induced by the contrast procedure had no reliable effect on syllable identification. However, in a control study, changes in physical rate that produced equivalent changes in perceived rate did reliably alter identification of the syllables. Phonetic identification is thus influenced by the physical rate of the speech, not its perceived rate.