Three experiments investigated perception of audio-visual (A-V) speech synchrony in 4- to 10-month-old infants. Experiments 1 and 2 used a convergent-operations approach by habituating infants to an audiovisually synchronous syllable (Experiment 1) and then testing for detection of increasing degrees of A-V asynchrony (366, 500, and 666 ms) or by habituating infants to a detectably asynchronous syllable (666 ms; Experiment 2) and then testing for detection of decreasing degrees of asynchrony (500, 366, and 0 ms). Following habituation to the synchronous syllable, infants detected only the largest A-V asynchrony (0 ms vs. 666 ms), whereas following habituation to the asynchronous syllable, infants detected the largest asynchrony (666 ms vs. 0 ms) as well as a smaller one (666 ms vs. 366 ms). Experiment 3 investigated the underlying mechanism of A-V asynchrony detection and indicated that responsiveness was based on a sensitivity to stimulus-energy onsets rather than the dynamic correlation between acoustic and visible utterance attributes. These findings demonstrated that infant perception of A-V speech synchrony is subject to the effects of short-term experience and that it is driven by a low-level, domain-general mechanism. (Contains 4 figures.)