Dissociable reference frames in orientation recall: The oblique effect follows retinal coordinates, while repulsion from cardinal follows real-world coordinates.
Systematic differences in recall-error emerge when people report an orientation from memory after a brief delay. One is the classic oblique effect, with smaller replication errors for targets presented at cardinal compared to oblique orientations. Another is a repulsion away from the cardinal axes, with responses to near vertical and horizontal targets exaggerated to lie even further away from those axes than they actually were. To test the origins of these systematic differences in error, twelve participants were presented with randomly oriented gratings (between 1–180º) for 100 ms. on each trial, which they replicated (using a computer mouse) after a 1.5 s delay period. Critically, on half of the trials a rotating chin-rest tilted the head of participants 45º from upright – with tilt direction counterbalanced across participants. For several psychophysical experiments, many trials per tilt position were collected over the course of several days. Data show that the classic oblique effect is tied to a retinal coordinate frame, with better resolution for targets presented at orientations that are cardinal relative to the head, irrespective of its tilt. However, the repulsion from cardinal remained tied to real-world vertical and horizontal. We hypothesize that while the classical oblique effect is driven by retinal and cortical factors determined during visual development (such as the over-representation of cardinal orientations in visual cortex), the second 'repulsion' bias is due to a higher-level decisional component whereby representations are cropped relative to real-world cardinal coordinates. We furthermore found that when applying the same head-tilt manipulation with EEG, the population response over visual cortex represents a mixture of both retinal- and real-world reference frames.