EFFECT OF NOISE CONTRAST POLARITY AND TEMPORAL ASYNCHRONY ON VISUAL SENSITIVITY

We evaluated the effect of substitutive noise on contrast sensitivity within the context of linear (Fourier) and nonlinear (non-Fourier) vis ual processes. Orientation judgments for D6 (sixth spatial derivative of Gaussian) patterns were obtained from three visually normal subject s when random regions of the target and background were occluded by sm all (1.7 are min) pixel arrays that were either all of the same contra st polarity or a mixture of equal percentages of negative and positive contrast. The target was presented either synchronously or asynchrono usly with the occluding elements. Our results indicate that the manipu lation of noise characteristics in this way can bias performance eithe r toward a nonlinear process that is insensitive to noise contrast pol arity but sensitive to temporal asynchrony or toward a quasi-linear pr ocess that is sensitive to noise contrast polarity but insensitive to temporal asynchrony. These findings have relevance to models of the ef fect of spatial sampling on the visual performance of persons with ret inal disease. (C) 1998 Optical Society of America. [S0740-3232(98)0021 1-7]. OCIS codes: 330.1070, 330.1800, 330.6130, 330.5000, 330.5510.