Abstract
Systematic biases emerge when people report an orientation from memory after a brief delay. One such bias is the classic oblique effect, with smaller replication errors for targets presented at cardinal compared to oblique orientations. A second known bias is a repulsion away from the cardinal axes, with responses to targets near vertical and horizontal exaggerated to lie even further away from those axes. Here we wanted to test the origins of these biases. Twelve participants were presented with randomly oriented gratings (between 1–180º in 3º steps) on each trial for 100 ms. After a 1.5 s delay period a response probe appeared and participants replicated the target orientation using the mouse. Critically, on half of the trials a rotating chinrest tilted the head of participants 45º from upright – with tilt direction counterbalanced across participants. Participants switched between upright and tilted head positions every 60 trials, and 1800 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.
Meeting abstract presented at VSS 2017