Analysis of visual modulation sensitivity. III. Meridional variations in peripheral flicker sensitivity.

Critical flicker frequency (CFF) and modulation sensitivity were measured throughout the visual field as a function of meridian, eccentricity, and luminance. The stimulus conditions were designed to excite preferentially the long-wavelength-sensitive (R) cones in equal numbers at each retinal location. Temporal-frequency responses under these conditions can be partitioned into two components by following the analysis of Kelly [J. Opt. Soc. Am. 51, 422 (1961)]: a high-frequency linear component unaffected by the mean luminance level and a nonlinear adaptive component that conforms to Weber's law of proportionality to luminance. The results suggest that the time constant of the linear component varies to some extent with meridian at a constant eccentricity, in addition to the substantial increase with eccentricity along all meridians. Retinal variations in sensitivity of the nonlinear, adaptive aspect of the visual response were small when equal numbers of cones were stimulated, and the variations did not account for the changes in CFF with either eccentricity or meridian.