Temporal recalibration during asynchronous audiovisual speech perception.

We investigated the consequences of monitoring an asynchronous audiovisual speech stream on the temporal perception of simultaneously presented vowel-consonant-vowel (VCV) audiovisual speech video clips. Participants made temporal order judgments (TOJs) regarding whether the speech-sound or the visual-speech gesture occurred first, for video clips presented at various different stimulus onset asynchronies. Throughout the experiment, half of the participants also monitored a continuous stream of words presented audiovisually, superimposed over the VCV video clips. The continuous (adapting) speech stream could either be presented in synchrony, or else with the auditory stream lagging by 300 ms. A significant shift (13 ms in the direction of the adapting stimulus in the point of subjective simultaneity) was observed in the TOJ task when participants monitored the asynchronous speech stream. This result suggests that the consequences of adapting to asynchronous speech extends beyond the case of simple audiovisual stimuli (as has recently been demonstrated by Navarra et al. in Cogn Brain Res 25:499-507, 2005) and can even affect the perception of more complex speech stimuli.