Effects of speaking rate on phonetic perception: Contribution of visual information

Abstract

It is by now well-established that the listener makes very precise adjustments for speaking rate when perceiving the phonetic structure of speech. The concern of the present investigation was the nature of the rate information to which the listener adjusts. When a speaker changes rate, he or she alters the timing of articulatory gestures. One consequence is a change in the acoustic form of the speech signal—for example, a change in its overall duration. Such changes provide auditory information about speaking rate. Additionally, however, some of these articulatory gestures are visible on the face of the talker and, therefore, provide visual information about the talker's rate of speech. We asked whether the effective rate information for phonetic perception is limited to the auditory domain or, alternatively, whether visual information about rate from the face also influences the perception of speech. To investigate this question, we paired acoustic versions of /bi/ and /pi/ produced by a talker, at a medium rate of speech, with a video display of the same talker producing these syllables at fast and slow rates of speech. The phenomenal experience that resulted from any given audio-visual pairing was that of a unified percept of a single syllable, produced at a single rate of speech. We found that the variation in the speaking rate of the syllable on the video display (with the rate of the acoustic syllable kept constant) systematically influenced not only the judged rate of the syllable, but also the identification of the syllable as /bi/ or /pi/. These results suggest that at least under some circumstances, auditory and visual information about articulatory timing jointly influence phonetic perception. [Research supported by NIH.]