TEMPORAL CONSTRAINTS ON THE MCGURK EFFECT

Three experiments are reported on the influence of different timing re lations on the McGurk effect. In the first experiment, it is shown tha t strict temporal synchrony between auditory and visual speech stimuli is not required for the McGurk effect. Subjects were strongly influen ced by the visual stimuli when the auditory stimuli lagged the visual stimuli by as much as 180 msec. In addition, a stronger McGurk effect was found when the visual and auditory vowels matched. In the second e xperiment, we paired auditory and visual speech stimuli produced under different speaking conditions (fast, normal, clear). The results show ed that the manipulations in both the visual and auditory speaking con ditions independently influenced perception. In addition, there was a small but reliable tendency for the better matched stimuli to elicit m ore McGurk responses than unmatched conditions. In the third experimen t, we combined auditory and visual stimuli produced under different sp eaking conditions (fast, clear) and delayed the acoustics with respect to the visual stimuli. The subjects showed the same pattern of result s as in the second experiment. Finally, the delay did not cause differ ent patterns of results for the different audiovisual speaking style c ombinations. The results suggest that perceivers may be sensitive to t he concordance of the time-varying aspects of speech but they do not r equire temporal coincidence of that information.