Cass, J.; Talbot, D.

Our judgments of the world are shaped by what we have just seen. This serial dependence is often treated as one bias, but it can constitute opposing influences: an attractive pull toward recent input and a repulsive push away from it. These have been linked to different stages, decisional and perceptual, but separated only for simple visual features. We asked whether the same separation holds for a socially significant category, the human body. Observers categorised images of male bodies as low or high on body fat and muscularity (binary choice, N = 74); a trial-level analysis estimated the perceptual and decisional contribution to each judgment. For body fat, the perceptual contribution was repulsive and clearly tuned, following a derivative-of-Gaussian profile peaking at a moderate difference between successive bodies ({sigma} {approx} 5.6 standardised units), while the decisional contribution was attractive; the dissociation held in most observers. Muscularity showed the same attractive decisional bias, but its perceptual tuning emerged only at longer viewing times, where its width approached that for body fat, indicating a difference in resolvability rather than an absence of tuning. To our knowledge, this is the first estimate of the tuning of the perceptual repulsion channels from binary categorisation of continuously varying stimuli, the first separation of perceptual and decisional components in body perception, and the first evidence of serial dependence for male bodies. Perception emphasises how a body differs from the previous one while the decision favours continuity, a division of labour spanning low-level features to high-level body judgments.