backward masking

n. Backward masking is a form of masking in which the target (i.e., a to-be-identified item) temporally precedes that mask stimulus (an image, a tone, or a chemical). The mask can occur immediately after the target or after a delay. The difficulty in one's ability to perceive the target in this situation is referred to as the masking effect. This effect is influenced by the interval between the presentation of the mask and target, the location of the mask and target relative to each other (e.g., whether two images are superimposed or not), the intensity of the mask and target (e.g., the brightness of a letter), as well as other characteristics (e.g., direction of the line segments). All else being equal, masking is generally stronger as the interval between the presentation of the mask and that of the target is reduced.

An example of backward masking: in general, the participant is asked to look at the center of a computer screen and identify words that appear in that location. As the participant focuses on the screen, a word occurs (e.g., bird),followed either immediately or after a short delay (e.g., 0.1 second or 100 milliseconds) by a mask (e.g., &&&&). The presence of the ampersand pattern in the same location as the word makes it difficult for the participant to perceive two separate images; instead the two images become intermixed. The intermixing of the mask and target images makes identifying the word more difficult than if the mask had not occurred. This sequence of events is an example of backward masking in the visual domain.

- DGr

► See also masking