Figure 1.

Stimuli. Motion stimuli were composed of two types of gratings, an isoluminant red–green grating and a contrast-modulated noise grating (with same expected luminance throughout). (a) A five-frame motion sequence with a green advantage; each successive frame displaced 90° consistently to the right or left relative to its predecessor. Frames are presented one on top of the other. The color frames consist of saturated green, |G| = 1, and pale red, |R| = 0.32. The arrow indicates the typical direction of apparent motion. (b) Graphic representation of color in a green-advantage frame: |R| − |G| vs. x. (c) A neutral five-frame motion sequence: |R| = |G| = 1. The direction of apparent motion in this display is determined by attention, as indicated by arrows. (d) Graphic representation of color in a frame in which the red advantage is zero: |R| − |G| vs. x.