Illusory Motion Reversals are Driven by Temporal Frequency Adaptation

The continuous wagon wheel illusion, also known as illusory motion reversal (IMR), refers to the intermittent perception of illusory motion in the opposite direction while viewing movement. Previous studies suggest IMR occurs most for stimuli with a temporal frequency of ∼10Hz. This was taken as evidence for IMR resulting from temporal sub-sampling by a visual system with a fixed sampling rate. Other explanations have highlighted similarities between IMR and motion aftereffects, speculating that IMR is a form of adaptation induced ‘motion during-effect’. To investigate these possibilities we first estimated the optimal rates for IMR using colour and luminance defined movements. The optimal rate for colour defined movement was ∼4Hz, whereas the optimal rate for luminance defined motion was ∼10Hz, contradicting the idea of a global sampling rate for the visual system. We then investigated the effect of TF adaptation on subsequent 10Hz tests. IMR was maximal after adaptation to ∼1Hz or 30Hz, and minimal after adaptation to 20Hz. Contrary to what would be expected of a motion during-effect, adaptation TF tuning was not modulated by direction of motion, and the effects of directionless flicker were qualitatively equivalent. Our results suggest that IMR is driven by adaptation of TF channels.