Beyond self-generated perceptual history: Other’s prior perceptual decisions bias one’s own perceptual decision

Our perceptual experiences are systematically biased by recent perceptual history, a phenomenon known as serial bias. Yet prior research has focused exclusively on self-generated perceptual history, even though we constantly observe others’ perceptual decisions that could also influence how we see the world. The present study investigated this possibility. In the experiments, pairs ofcollege students (N = 66) alternated trials in an orientation estimation task, with serial bias assessed following the partner's trial. Orientation reports were biased away from the partner'sprior report even if it was task irrelevant. Follow-up experiments revealed that this between-individual serial bias was driven by post-perceptual decisional mechanisms rather than low-levelsensory processes alone. Although limited to a controlled laboratory task, these findings demonstrate that others' perceptual decisions are automatically incorporated into one's own perceptual history, fundamentally broadening our understanding of what constitutes perceptual history and how it shapes perception.