The flash duration producing maximum brightness-enhancement changes as a power function of luminance, that is, the time locus of the Broca–Sulzer flash duration TB, decreases as luminance L increases: TB = k × Lβ, where β is the duration exponent. The exponent of TB was estimated for 1-deg white flash with five luminance levels covering the range 3.94–1.94 log cd/m2 in steps of 0.5 log unit. The retinal loci tested were fovea, 10-, 20-, 30-, 40-, 50-, and 60-deg temporal eccentricities of the dark-adapted human right eye. The following method of brightness maximization was used: the observer adjusted the duration of constant luminance flashes to produce a maximally bright flash. Duration was adjusted by rotating a microprocessor-based potentiometer. The results showed that the duration of the brightest flash TB decreased as L increased with the negative power exponent. Furthermore, the size of the negative exponent decreased as a function of increasing retinal eccentricity. Time-dependent brightness processing in the fovea and periphery is discussed in terms of the psychophysical brightness power function.
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