Forward Masking

Forward masking is a perceptual phenomenon, the mirror image of backward masking documented elsewhere in this section, in which the detection or identification of a stimulus is impaired because a different stimulus, the mask, was presented shortly beforehand rather than afterward, so that the earlier stimulus interferes with perception of the one that follows it. The effect has been studied extensively in auditory research, where a preceding tone or noise burst can raise the threshold needed to detect a following brief sound, and in vision, where a preceding bright flash or pattern can reduce the visibility of a subsequently presented target. Researchers generally attribute forward masking to persisting neural activity or adaptation triggered by the first stimulus that has not yet fully subsided by the time the second stimulus arrives, so that the sensory system processing the target is still partly occupied with, or desensitized by, its response to the mask. Forward and backward masking are frequently studied together because comparing how each varies with the timing gap between mask and target, and with the physical similarity between them, has helped researchers build detailed models of how quickly sensory information is processed, and of the specific processing stages at which one stimulus can interfere with the perception of another.