Neural delays, visual motion and the flash-lag effect.

In the primate visual system, there is a significant delay in the arrival of photoreceptor signals in visual cortical areas. Since Helmholtz, scientists have pondered over the implications of these delays for human perception. Do visual delays cause the ' position of a moving object to lag its 'real' position? This question has recently been re-evaluated in the context of the flash-lag phenomenon, in which a flashed object appears to lag behind a moving object, when physically the two objects are co-localized at the instant of the flash. This article critically examines recent accounts of this phenomenon, assesses its biological significance, and offers new hypotheses.