Factors modulating the temporal perception of audiovisual speech stimuli
Poster Presentation

Argiro Vatakis
Experimental Psychology, University of Oxford

Charles Spence
Experimental Psychology, University of Oxford

     Abstract ID Number: 94
     Full text: Not available
     Last modified: March 17, 2006
     Presentation date: 06/21/2006 8:30 AM in Hamilton Building, McNeil Theatre
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Abstract
We report a series of 4 experiments designed to investigate the factors modulating people’s sensitivity to asynchrony for audiovisual speech stimuli. Short speech video clips were presented randomly at a range of stimulus onset asynchronies (SOAs) using the method of constant stimuli. Participants made unspeeded temporal order judgments (TOJs) regarding which stream appeared to have been presented first. The first major finding to emerge from our experiments was that people’s sensitivity to asynchrony in brief speech stimuli is much better than has been suggested on the basis of previous research (that has typically used continuous speech streams as stimuli). Furthermore, significant differences in temporal discrimination accuracy (as measured by the just noticeable difference; JND) were obtained as a function of the place of articulation, backness, height of lip-opening, and lip-rounding, while no such differences were found for any of the other articulatory features tested. Interestingly, our results also revealed that highly-salient visual-speech stimuli typically require smaller visual leads for the point of subjective simultaneity (PSS) to be achieved than do less-salient visual-speech stimuli. Finally, the ‘assumption of unity’ (Welch & Warren, 1980) was also found to modulate TOJ performance for speech (but not for non-speech) stimuli.