Masking by spatially-modulated gratings.

Contrast- or quasi-frequency-modulated masker gratings consisting of three high frequency components (8.8, 11 and 13.2 c/deg) affect the detectability of a 2.2 c/deg signal grating, to an extent that is strongly dependent upon the relative phase between signal and masker. Unmodulated high frequency maskers have no such phase-dependent effects. This paper explores the possibility that the visual system's nonlinear response to luminance is responsible for these phenomena. A specific hypothesis is proposed according to which the effects of the spatially modulated maskers are due entirely to a distortion product at 2.2 c/deg caused by the visual nonlinearity. Although some of the predictions of this hypothesis are borne out by the experimental findings, others are contradicted.