Observer's control of the moving stimulus increases the flash-lag effect

The flash-lag effect (FLE) consists in perceiving a briefly presented stationary stimulus to lag behind an aligned moving stimulus. This study investigates the effects of actively controlling the moving stimulus. By means of a robotic arm, observers continuously moved a dot along a circular trajectory, and a flash was displayed closely at unpredictable times. In two experiments, we found that the FLE was larger when participants controlled the moving stimulus, compared to a computer-controlled condition. Two control conditions tested the possibility that the observed modulation of the FLE was due to visuo-spatial attention or dual-task factors. This study provides evidence that the motor system interacts with and possibly speeds up the processing of a moving visual stimulus when the observer controls its movement.