Effects of luminance and external temporal noise on flicker sensitivity as a function of stimulus size at various eccentricities.

We studied how the dependence of flicker sensitivity on stimulus size was affected by the eccentricity of the stimulus at high luminance, at low luminance (with quantal noise), and at high luminance with the addition of pure white temporal noise. Flicker sensitivity was measured as a function of stimulus size for temporal frequencies of 1-30 Hz with uniform sinusoidally flickering spots. Sensitivity first increased with increasing stimulus size but then the increase saturated. At high luminance the saturation took place at larger stimulus sizes with increasing eccentricity. Without externally added temporal noise the maximum sensitivity was higher at the fovea than in the periphery at temporal frequencies of 1-10 Hz, but at 30 Hz this situation reversed. Therefore only the ascending parts of the spatial integration curves from various eccentricities could be superimposed by size scaling. E2, the eccentricity at which the spatial scale doubles, was found to be 2.2-2.7 deg for 1-10 Hz but 4.4 deg for 30 Hz. When enough temporal noise was added, performance at all stimulus sizes studied could be made independent of eccentricity by spatial scaling, since noise reduced maximum sensitivities to a constant level at all eccentricities. E2 was found to be 4.1 deg for 3 Hz and 7.2 deg for 30 Hz. When light level was reduced by 3 log10 units, foveal and peripheral flicker sensitivity functions almost superimposed at all stimulus sizes studied. Hence, at 1 and 3 Hz E2 was very large, about 70 and 22 deg, respectively. At 10 and 30 Hz no size scaling was needed and E2 was therefore infinite.