Reversed effects of prior choices in cross-modal temporal decisions.

Perception of a current stimulus is influenced by one's immediately preceding sensory experience. This phenomenon, termed "serial dependence", affects perception of isochronous rhythm. However, it is unknown whether serial dependence affects perception of more complex temporal dynamics, such as changing tempo. Here, we tested the influence of serial dependence on perception of changes in tempo of a three-beat (two-interval) rhythm. In Experiment 1, participants were asked to classify whether visual or auditory stimulus rhythms (tested in separate blocks) had "accelerating" or "decelerating" tempo. In Experiment 2, the visual and auditory rhythms were interleaved to investigate serial dependencies across modalities. Current decisions were attracted toward previous choices, but only in the uni-modal conditions (when the previous and current trials were from the same modality, seen in both Experiments 1 and 2, for both vision and audition). Surprisingly, in the cross-modal conditions (of Experiment 2), the opposite - a repulsive effect of previous choices - was observed. Besides the effects of previous choices, previous stimuli (tempo changes in the previous trial) also influenced current decisions - exerting a repulsive effect in the uni-modal conditions (for both modalities in Experiment 2, and auditory, but not visual, in Experiment 1) - which was notably absent in the cross-modal conditions. Repulsive effects of previous choices from a different modality, in contrast to attractive choice effects within the same modality, suggests that changing modalities triggers choice switching. These results, along with the lack of influence of previous stimuli cross-modally, suggest that modality consistency is an important factor for serial dependence in the perception of rhythm.