Decisional dynamics underlie attractive and repulsive serial dependence with delayed estimation

Studies on serial dependence demonstrated that perceptual reports exhibit systematic biases in relation to the task-irrelevant previous stimulus. Does this phenomenon reflect distortions in the stimulus representation itself or biases in post-perceptual decision-making? To answer this question, the present study investigated how quickly the decision for a new stimulus is initiated by measuring response initiation time (RTI) and how the decision unfolds over time by measuring response trajectories for the mouse reports in orientation delayed estimation tasks. We hypothesized that the two variables (i.e., RTI and response trajectory) should be independent of the previous stimulus if the bias is driven by distortions in the representation itself, whereas they should vary systematically in relation to the previous stimulus if the bias is driven by post-perceptual decision processes. In two experiments, we found that 1) RTI was slower when the current stimulus was similar to the previous stimulus, indicating that the decision was more difficult for such trials, and 2) mouse reports started from the opposite side of the previous stimulus, indicating that the decision was executed by avoiding the previous stimulus. Critically, similar decisional dynamics were observed irrespective of the direction of serial dependence. Together, these results provide converging evidence that both repulsive and attractive serial dependence are driven by processes that integrate previous stimuli into the decision for a new stimulus, placing significant constraints on the theories that assume that serial dependence reflects the distortions in the representation itself.