Attraction to hierarchical feature memory explains orientation bias
When recalling the orientation of recent stimuli, observers are systematically biased away from the cardinal axes. The prevailing explanation is that this ''anti-cardinal bias'' arises because cardinal orientations are encoded with greater neural resources and therefore less noise, consistent with efficient coding of environmentally common features. Under this account, the bias should occur independently for each stimulus; any serial attraction towards previously seen orientations should be independent of absolute orientation. By contrast, we find that serial effects in orientation recall are unexpectedly strong and reflect a hitherto unrecognised hierarchical interaction, consistent with recurrent connectivity across hierarchies of sensory processing in the brain. We found that serial dependence in visual orientation recall is dominated not by attraction to the previous orientation itself, but to a compound feature representing both a tilt and its mirror reflection about the cardinal axes. Consistent with greater spatial abstraction at higher levels, the influence of this compound feature persisted across the visual midline, whereas orientation-specific effects weakened between hemifields. We developed a quantitative model based on the optimal combination of a noisy representation of the current stimulus with a hierarchical memory trace incorporating these compound features. Remarkably, although the coding fidelity was uniform across angles, this model accurately reproduced not only the serial dependence, but also the anti-cardinal bias. Our results suggest that memory traces are not isolated to single features, but reflect compound reactivation of hierarchical representations. Furthermore, they reveal that inference across hierarchical representations can generate systematic perceptual distortions previously ascribed to coding constraints.