Figure 1.

Schematic illustration of one method used by Lu et al. (2) to manipulate salience within a chromatically defined pattern. (A) The standard stimulus configuration, which has been used in many previous experiments, consists of a pattern of red and green stripes on a chromatically intermediate (gray) background. The luminances of the stripes and background are equivalent (i.e., isoluminant). When this stimulus is moved, its motion generally appears slower and more irregular that it truly is. Lu et al. (2) attribute this nonveridical percept to the fact that the red and green stripes are of nearly equal salience. (B) If the green stripes are replaced with a gray color that is identical to background, the red stripes are more likely to be perceived as foreground and hence more salient than the gray. The result is a robust percept of motion, despite the fact that the red/gray pattern—like the red/green pattern—is isoluminant and defined only by a chromatic difference. Lu et al. (2) argue that this percept of “high-quality isoluminant motion” is a product of the proposed third-order motion system.