Eye movements affect the perceived speed of visual motion

Eye movements add a constant displacement to the visual scene, altering the retinal-image velocity. Therefore, in order to recover the real world motion, eye-movement effects must be compensated. If full compensation occurs, the perceived speed of a moving object should be the same regardless of whether the eye is stationary or moving. Using a pursue-fixate procedure in a perceptual matching paradigm, we found that eye movements systematically bias the perceived speed of the distal stimulus, indicating a lack of compensation. Speed judgments depended on the interaction between the distal stimulus size and the eye velocity relative to the distal stimulus motion. When the eyes and distal stimulus moved in the same direction, speed judgments of the distal stimulus approximately matched its retinal-image motion. When the eyes and distal stimulus moved in the opposite direction, speed judgments depended on the stimulus size. For small sizes, perceived speed was typically overestimated. For large sizes, perceived speed was underestimated. Results are explained in terms of retinal-extraretinal interactions and correlate with recent neurophysiological findings.