Detection of Auditory-Visual Asynchrony in Speech and Nonspeech Signals

Two experiments were conducted to examine the temporal limitations on the detection of asynchrony in auditory-visual (AV) signals. Each participant made asynchrony judgments about speech and nonspeech signals presented over an 800-ms range of AV onset asynchronies. Consistent with previous findings, all conditions revealed a wide window of several hundred milliseconds over which AV signals were judged to be synchronous. In addition, signals in which the visual component led the auditory component were more likely to be judged as synchronous than signals in which the auditory component led the visual component. In contrast with earlier reports (Dixon & Spitz, 1980; McGrath & Summerfield, 1985), the present results also demonstrated a similar AV synchrony window for speech and nonspeech signals, even when these signals were matched for duration. Visual phonetic characteristics of the speech signals, however, did influence the size and shape of the AV synchrony window. Finally, the onset of the relevant aspects of the stimulus, rather than the duration or offset, was most important for asynchrony judgments for both speech and nonspeech signals. Relationships with recent data on neural mechanisms of multisensory enhancement and convergence are discussed.