Serial dependence does not build up to central tendency bias in orientation judgments

Perception is shaped by sequential biases operating on multiple timescales, including short-term serial dependence, medium-term central tendency bias (CTB), and long-term effects like the cardinal bias in orientation judgments. Although serial dependence has been widely observed in orientation judgments, CTB has not been reliably demonstrated despite its prevalence in other stimulus types. In this study, we investigated how these biases co-occur by comparing orientation judgments in two conditions: one with stimuli sampled from a full circular uniform distribution and another from a restricted section of orientations. Participants exhibited a cardinal bias away from cardinal orientations and an attractive serial dependence in both conditions. Contrary to expectations, no CTB was observed in the section condition independent of cardinal bias. Instead, participants showed a repulsive bias away from the center of the stimulus distribution, independent of cardinal biases. This repulsive bias persisted after controlling for serial dependence, suggesting that it may reflect a medium-term effect rather than a statistical artifact. The results challenge models that posit a shared mechanism for CTB and serial dependence and show that attractive serial dependence is not sufficient for a CTB to emerge. These findings highlight the need to account for stimulus space geometry and both attractive and repulsive sequential biases.