Audio-visual interactions with intact clearly audible speech.

The effects of viewing the face of the talker (visual speech) on the processing of clearly presented intact auditory stimuli were investigated using two measures likely to be sensitive to the articulatory motor actions produced in speaking. The aim of these experiments was to highlight the need for accounts of the effects of audio-visual (AV) speech that explicitly consider the properties of articulated action. The first experiment employed a syllable-monitoring task in which participants were required to monitor for target syllables within foreign carrier phrases. An AV effect was found in that seeing a talker's moving face (moving face condition) assisted in more accurate recognition (hits and correct rejections) of spoken syllables than of auditory-only still face (still face condition) presentations. The second experiment examined processing of spoken phrases by investigating whether an AV effect would be found for estimates of phrase duration. Two effects of seeing the moving face of the talker were found. First, the moving face condition had significantly longer duration estimates than the still face auditory-only condition. Second, estimates of auditory duration made in the moving face condition reliably correlated with the actual durations whereas those made in the still face auditory condition did not. The third experiment was carried out to determine whether the stronger correlation between estimated and actual duration in the moving face condition might have been due to generic properties of AV presentation. Experiment 3 employed the procedures of the second experiment but used stimuli that were not perceived as speech although they possessed the same timing cues as those of the speech stimuli of Experiment 2. It was found that simply presenting both auditory and visual timing information did not result in more reliable duration estimates. Further, when released from the speech context (used in Experiment 2), duration estimates for the auditory-only stimuli were significantly correlated with actual durations. In all, these results demonstrate that visual speech can assist in the analysis of clearly presented auditory stimuli in tasks concerned with information provided by viewing the production of an utterance. We suggest that these findings are consistent with there being a processing link between perception and action such that viewing a talker speaking will activate speech motor schemas in the perceiver.