In space, the past can be recast but not the present

We address the relationship between perception and spatial, working memory. Specifically, we argue that perceptual experience following the creation o f a representation of target location affects it in a systematic way. We de signed a motor task in which observers had to point to the initial or final position of a horizontally drifting target embedded in a vertically drifti ng background. The target was perceived as having an illusory motion compon ent in a direction opposite that of the inducer dots [Duncker, 1938, Source Book of Gestalt Psychology (London: Kegan Paul, Trench, Trubner and Co)]. For both positions, there was an identical time delay before the observer c ould respond. Nonetheless, estimates of the initial target position were si gnificantly biased by the illusion in a direction opposite the perceived ta rget motion, and both bias and variability were significantly greater than those of the target's final position. In prior studies on positional accura cy with induced displacement, a delay before a pointing response led to an unbiased position estimate obtained without delay to become biased, leading investigators to argue for a long-lasting, inaccurate cognitive system tha t overrules an accurate, nonetheless transient, motor one (Bridgeman et al, 1997, Perceptual Psychology 59 456-469). Since the same motor task with id entical delay on either position yielded different outcomes, a hypothesis b ased on distinct motor and cognitive representations of visual space is unt enable here. Instead, we argue that an online representation of the target' s original position is updated in an ongoing fashion in order to reconcile the perceived illusion with the veridically perceived present (current targ et location).