Visual masking

Visual masking occurs when the perception of one stimulus, called a target, is affected by the presence of another stimulus, called a mask. With respect to time, there are three different types of masking – forward, backward, and simultaneous. These correspond to trials where the mask precedes the target, follows the disappearance of the target, or appears at the same time as the target, respectively. In the spatial domain, there are two different types of masking: pattern masking and metacontrast. Pattern masking occurs when the target and mask are presented within the same retinal location, and metacontrast occurs when the mask does not overlap with the target location.