Discrimination of auditory-visual synchrony

Discrimination thresholds for temporal synchrony in auditory-visual sentence materials were obtained on a group of normal-hearing subjects. Thresholds were determined using an adaptive tracking procedure which controlled the degree of audio delay, both positive and negative in separate tracks, relative to a video image of a female speaker. Four different auditory filter conditions, as well as a broadband speech condition, were evaluated in order to determine whether discrimination thresholds were dependent on the spectral content of the acoustic speech signal. Consistent with previous studies of auditory-visual speech recognition which showed a broad, asymmetrical range of temporal synchrony (audio delays roughly between -40 ms and +240 ms) for which intelligibility was basically unaffected, synchrony discrimination thresholds also showed a broad, asymmetrical pattern of similar magnitude (audio delays roughly between -45 ms and 200 ms). No differences in synchrony thresholds were observed for the different filtered bands of speech, or for broadband speech. These results suggest a fairly tight coupling between a subject's ability to detect cross-modal asynchrony and the intelligibility of auditory-visual speech materials.