APA Dictionary of Psychology

n. a form of forward masking in which the perception of a visible stimulus (the target) is altered by the prior presentation of another visual stimulus (the mask) in a different spatial location. The target is often a small dot, whereas the mask is a ring that surrounds it. Each stimulus is presented very briefly (10–100 ms), at intervals that are varied systematically, and the quality of the target’s percept is measured. Compare metacontrast.