A number of recent studies have shown that early visual areas have a spatially asymmetric response to visual motion: there is a stronger fMRI response at the origin of motion or trailing edge of a moving pattern (Whitney, et al., Science, 2003; Koyama, et al., SfN, 2003). Some studies reported that the effect is significant but small (Liu, et al., SfN, 2004; Ashida & Smith, VSS, 2005); the increased response at the trailing edge of the moving pattern corresponds to a 1-2 mm shift in the location of that edge. However, the size and nature of the effect is difficult to interpret since no experiment has systematically examined how the spatially inhomogeneous response correlates to perception. To address this question, we used a spatial correlation technique (similar to Haxby, et al., 2001), which provides a more precise estimate of the perceptual correlate of this activity. We presented Gabor patterns (with stationary envelopes) containing a carrier that could drift toward or away from the fovea. In separate ...