Abstract

Adaptation to videos of human locomotion (videos recorded from the London Marathon) affects observers’ subsequent perception of human locomotion speed: normal speed test stimuli are perceived as being played in slow-motion after adaptation to fast-forward stimuli and conversely, are perceived as being played in fast-forward after adaptation to slow-motion stimuli. In this study we investigated whether the presence of recognisable human motion in the adapting stimulus is necessary for the effect. The adapting stimuli were spatially scrambled: horizontal pixel rows were randomly shuffled. The same shuffled order was used for all frames preserving horizontal motion information, but ensuring no human form could be recognised. Results showed that the after-effect persisted despite spatially scrambling the adapting stimuli; human motion is not a necessary requirement for the locomotion after-effect. The after-effect seems to be driven by adaptation in relatively low-level visual channels rather than the high-level processes that encode human motion.