1. in perception, the partial or complete obscuring of one stimulus (the target) by another (the masker). The stimuli may be sounds (see auditory masking), visual images (see visual masking), tastes, odorants, or tactile stimuli. Forward masking occurs when the masker is presented a short time before the target stimulus, backward masking occurs when it is presented shortly afterward, and simultaneous masking occurs when the two stimuli are presented at the same instant. Also called perceptual masking.

2. in statistics, the obscuring of the effect of one variable by the effect of another variable. For example, a researcher interested in whether risky sexual behavior is related to alcohol use might find that an experience of sexual abuse exerts a stronger influence on sexual behavior, thus masking the effect of alcohol use. —mask vb.