Two components of rapid temporal recalibration: a stimulus-driven shift and a decisional carryover dissociate across the senses

Multisensory synchrony judgments depend on recent history: the point of subjective simultaneity (PSS) shifts toward recently experienced timing relationships. This shift, known as rapid temporal recalibration, is almost always interpreted as perceptual, a change in when events appear simultaneous. Yet serial dependence in such judgments can arise from two mechanistically distinct sources that a raw PSS shift cannot separate: a genuine perceptual realignment, which slides the psychometric function sideways along the multisensory asynchrony axis (an odd effect), and a decisional carryover, a bias to repeat the previous verdict, which lifts the function vertically without moving the PSS (an even effect). We re-analysed eight published datasets investigating rapid recalibration spanning audiovisual, audiotactile, and visuotactile pairings and audiovisual speech, decomposing serial dependence into these two components within a single mixed-effects model. The components dissociated by modality: perceptual recalibration was robust for audiovisual pairs but weak for audiotactile and absent for visuotactile pairings, whereas the decisional carryover was largest for the tactile pairings and weak for audiovisual pairings, so that the two traded off across the senses. In audiovisual speech, the decisional carryover was gated by the spoken syllable but not by the talkers identity and did not persist beyond one trial, identifying it as a content-specific, one-step decision memory rather than a motor habit or a multi-trial store. Separating the perceptual and decisional contributions to a timing judgment thus re-draws the map of temporal recalibration and revises several conclusions drawn from the undecomposed PSS.