Serial dependence carries the action that produced the previous report

Serial dependence pulls current judgments toward the recent past, but what is carried forward is debated: the previous stimulus, the previous decision, or something about the report itself. Three magnitude-reproduction experiments separated these sources. Participants viewed dot arrays that varied independently in duration and numerosity, then reproduced the cued dimension by holding a key while a display accumulated, so that both magnitudes were produced through the same action. A response-history model partitioned the attraction into previous-stimulus and previous-response paths. The previous response predicted cross-dimensional attraction after controlling for the previous and current stimuli: a numerosity report biased the next duration judgment and vice versa (Experiment 1), also when each task used its own response key (Experiment 2). A task switch weakened this carryover without abolishing it. Experiment 3 randomized, trial by trial, whether a reported number required a long or a short key hold. The influence of a previous number on the next duration judgment changed with this mapping, showing that reported value alone did not account for carryover. Conventional stimulus-based measures showed none of this cross-task history. Serial dependence can therefore carry the trace of the action through which a previous judgment was expressed, bounded but not gated by task context.