The flash-lag effect in ball sports players

Estimating motion and trajectories is a core function of human visual system. It is particularly relevant for ball sports players such as baseball or tennis players, who must accurately catch or hit a ball to win their game. The flash-lag illusion is a motion-based illusion where one will see a transiently appearing “flash” lagging behind a moving object. It could be caused by predictive mechanisms which help to anticipate the position of the moving object. In this study, we wanted to test whether subjects who are trained at anticipating trajectories such as ball sports players are particularly sensitive to that illusion. We tested and compared three groups of participants, all students from the Université de Montréal: ball sports players, non-ball sports athletes, and controls on a standard flash-lag effect paradigm. A bar was horizontally moving on screen and a flashed bar was presented either above or below the moving bar. The participants had to report whether the flashed bar appeared left or right relative to the moving bar. We observed a typical flash-lag effect in all groups with no difference between groups. This suggest that the flash-lag effect could not be due to anticipation mechanisms (e.g. latency difference or mis localization) or that training those mechanisms has no effect.