Spatial facilitation is involved in flash-lag effect.

The flash-lag effect (FLE) is the perceptual phenomenon in which a flash adjacent to a continuously moving object is perceived behind it. Horizontal propagation of activity could explain a shorter latency for moving than for flashed objects but, to our knowledge, no psychophysical data supporting this has been given. We show that two concurrent moving stimuli increase the FLE, presumably due to a latency decrease in movement perception. Our results support the idea that spatial facilitation along the trajectory of a moving object reduces movement perception delay and, therefore, sustains an involvement of latency differences in FLE generation.