The role of visual information in the processing of

Abstract
Visual information provided by a talker’s mouth movements can influence the perception of certain speech features. Thus, the “McGurk effect” shows that when the syllable /bi/ is presented audibly, in synchrony with the syllable /gi/, as it is presented visually, a person perceives the talker as saying /di/. Moreover, studies have shown that interactions occur between place and voicing features in phonetic perception, when information is presented audibly. In our first experiment, we asked whether feature interactions occur when place information is specified by a combination of auditory and visual information. Members of an auditory continuum ranging from /ibi/ to /ipi/ were paired with a video display of a talker saying /igi/. The auditory tokens were heard as ranging from /ibi/ to /ipi/, but the auditory-visual tokens were perceived as ranging from /idi/ to /iti/. The results demonstrated that the voicing boundary for the auditory-visual tokens was located at a significantly longer VOT value than the voicing boundary for the auditory continuum presented without the visual information. These results demonstrate that place-voice interactions are not limited to situations in which place information is specified audibly. In three follow-up experiments, we show that (1) the voicing boundary is not shifted in the absence of a change in the global percept, even when discrepant auditory-visual information is presented; (2) the number of response alternatives provided for the subjects does not affect the categorization or the VOT boundary of the auditory-visual stimuli; and (3) the original effect of a VOT boundary shift is not replicated when subjects are forced by instruction to \ldrelabel\rd the /b-p/auditory stimuli as/d/or/t/. The subjects successfully relabeled the stimuli, but no shift in the VOT boundary was observed.

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