Independent mechanisms of temporal and linguistic cue correspondence benefiting audiovisual speech processing

It is well established that in order to comprehend speech in noisy environments, listeners use the face of the talker in conjunction with the auditory speech. Yet how listeners use audiovisual speech correspondences along the multisensory speech processing pathway is not known. We engaged listeners in a pair of experiments using face rotation to partially dissociate linguistic and temporal information and two tasks to assess both overall integration and early integration specifically. In our first exploratory experiment, listeners performed a speech in noise task to determine which face rotation maximally disrupts speech comprehension and thus overall audiovisual integration. Our second experiment involved a dual pitch discrimination and visual catch task to test specifically for binding. The results showed that temporal coherence supports early integration, replicating the importance of temporal coherence seen for binding nonspeech stimuli. However, the benefit of temporal coherence was present in both upright and inverted positions, suggesting that binding is minimally affected by face rotation under these conditions. Together, our results suggest that different aspects of audio-visual speech are integrated at different stages of multisensory speech processing.