Sensitivity to auditory-visual asynchrony and to jitter in auditory-visual timing

Sensitivity to AV (auditory-visual) asynchrony was measured using brief tonal signals accompanied by a moving disk on a monitor. Stimuli were presented which either had synchronous audio and video or a positive or negative delay between audio and video. In a detection task, video delays of 29 ms and audio delays of 85 ms were just detectable. In a second experiment subjects had to judge whether the audio and the video were synchronous, whether audio preceded video, or the reverse. Results show a considerable variability in the range over which stimuli were judged to be synchronous. Typically, stimuli with audio delays in the range of -75 to 175 ms were judged synchronous. The distribution of synchronous responses had a mean of around 40 ms. The different results of the first and second experiment indicate that tolerance to AV delays is considerably larger than the just noticeable AV delay. In a next set of experiments several subsequent AV events were presented with variable amounts of jitter in the AV timing. Results of an experimental condition with a constant amount of overall AV delay indicate that the jitter was highly detectable (thresholds as low as 40 ms) even if an overall delay of up to 100 ms was presented. An additional experiment with a variable number of subsequent AV events shows that detecting an asynchrony in one AV event is more difficult than detecting jitter in multiple AV events.