Abstract
The mask effectiveness was measured in terms of critical ISI, varying dot density and duration of the mask. The resulting curves were inversed U-shaped functions of random dot density, indicating that the maximal effectiveness of the mask was obtained at about 50% dot density. As the mask duration increased, the U-shaped curves became more symmetrical. This effect was primarily due to an increase in the masking magnitude at lower dot density levels. At higher dot density levels, the mask effectiveness was nearly constant for mask durations of 5 ms or longer, depending upon dot density. The results suggest that a main factor of this type of masking is a confusion in a composite perceptual image which contains a representation of both the target and the mask.