Predictability affects the perception of audiovisual synchrony in complex sequences

The ability to make accurate audiovisual synchrony judgments is affected by the "complexity" of the stimuli: We are much better at making judgments when matching single beeps or flashes as opposed to video recordings of speech or music. In the present study, we investigated whether the predictability of sequences affects whether participants report that auditory and visual sequences appear to be temporally coincident. When we reduced their ability to predict both the next pitch in the sequence and the temporal pattern, we found that participants were increasingly likely to report that the audiovisual sequences were synchronous. However, when we manipulated pitch and temporal predictability independently, the same effect did not occur. By altering the temporal density (items per second) of the sequences, we further determined that the predictability effect occurred only in temporally dense sequences: If the sequences were slow, participants' responses did not change as a function of predictability. We propose that reduced predictability affects synchrony judgments by reducing the effective pitch and temporal acuity in perception of the sequences.