Brightness exponent for the periphery in the Bloch region.

Using a method of direct magnitude estimation, perceived brightness was measured in the dark-adapted eye with brief flashes of varying duration in the Bloch region (1-100 ms) and retinal lock (0 degrees-40 degrees) for the photopic luminance levels covering the range between 140 and 0.14 cd/m2 in steps of 1 log unit. Perceived brightness increased as a function of flash luminous energy (product of luminance and duration) up to critical duration of approximately 100 ms. The brightness power exponent for brief flash was found to be 0.48 +/- 0.01 in the fovea, whereas about 0.44 +/- 0.01 in the periphery.