GRATINGS THAT INDUCE PERCEPTUAL-DISTORTIONS MASK SUPERIMPOSED TARGETS

Masking is known to depend upon the relationship between the spatial-f requency content of target and mask. This relationship has been held c onstant in three experiments in order to investigate the separate cont ribution of the spatial parameters of the mask, in this case a grating with square-wave luminance profile. Thresholds for the detection of a probe target were highest when the background grating upon which the probe was superimposed had a spatial frequency of about 4 cycles deg(- 1) (experiment 1) and a duty cycle of 50% (experiment 3). In experimen t 2, the thresholds were strongly affected by the size of the backgrou nd grating even though the size of the target was small in proportion to the grating and remained constant. The increase in threshold was li nearly related to the area of visual cortex to which the grating proje cted. The spatial parameters of gratings that maximise masking are the refore the same as those that have been shown to be optimal for the in duction of perceptual distortions, suggesting a possible physiological mechanism for both the masking and the distortions.