Human performance in detecting audio-visual asynchrony.

The perception of audio-visual delays by human observers is typically characterized by two quantities: the point of subjective equality (PSE) and the sensitivity to asynchrony. The PSE can be derived from a temporal order judgment (TOJ) procedure or from the outcomes of a synchronous-successive response paradigm. Sensitivity to asynchrony is derived from the steepness of the response curve in the TOJ paradigm. In this contribution we present data that show that PSE estimates derived from TOJ measurements are much more variable across observers than those based on synchronous-successive data. Two synchronous-successive methods were used with different response categories: (1) two categories: asynchronous, synchronous, and (2) three categories: audio first, synchronous, video first. Both synchronous-successive methods yielded similar results. A slight influence of stimulus type on PSE estimates derived from synchronous-successive data was observed. To conclude, we analyzed discriminability values obtained with a two-alternative forced-choice procedure. Discriminability is better near the edge than in the middle of the synchronous response category. This suggests that categorical perception might play a role in audio-visual synchrony perception.