Abstract
We tested whether and how perceived retinal speed is modulated by head rotation. In three experiments, participants turned their heads while wearing a head-mounted display that presented a drifting visual stimulus moving in eye-centred coordinates. The task was to indicate the speed of the visual stimulus using a speed matching adjustment task. Several levels of retinal (from the stimulus) and extra-retinal (from the head turn) speed were paired and each pairing was tested in two configurations: congruent (both components moving in the same direction) or incongruent (components moved in opposite directions). Perceived retinal speed was also measured with the head stationary. We found that visual stimuli appeared to move faster when paired with a congruent head-turn and slower for incongruent head-turns, compared to the head stationary condition. The effect of head rotation on perceived speed increased with head-turn speed and was also tuned for relative direction, being strongest when the visual trajectory was aligned with the head turn and declining as the angle between them increased. This study demonstrates that visual speed perception is modulated by extra-retinal signals generated by head movements, adding to well-established findings showing that eye-movements modulate speed perception.