The influence of retinal and extra-retinal motion cues on perceived object motion during self-motion.

Eye, head, and body movement are intimately linked. During self-motion, the eyes track objects by a combination of vestibular reflexes and smooth pursuit eye movements but although the world appears stable during saccadic gaze changes, it does not appear stable during physical self-motion. We determined the amount by which a fixated object needed to be moved in space in order to appear earth stationary to a linearly moving observer. Observers were oscillated sinusoidally either passively or under their own control, under lit and fully darkened conditions. The visual targets always needed to move (in space) in the same direction as the observer to be judged as earth stationary. Targets needed to be moved more in order to be judged as earth stationary when movement was in the dark, rather than in the light, and also when movement was passive rather than when it was active. Efference copy motor signals, visual movement, and non-visual cues all contribute significantly and approximately additively to the estimate of self-motion. Errors in perceived self-motion can produce subsequent illusory visual motion.