Visual persistence: Effects of flash luminance, duration and energy

Abstract

Dark-adapted observers reported whether the offset of a test flash (30′ to the right of fixation) occurred before or after the onset of a probe flash (2°30′ to the left of fixation) as the interstimulus interval was varied. Visual persistence (the interstimulus interval at the point of subjeptive equality for test flash offset/probe flash onset) was found to decrease with either increases in flash duration or flash luminance. These effects were shown to be independent of differential visual latencies to the onsets of flashes. For equal-energy flashes (variable luminance and duration), persistence was constant up to 100 msec, and thereafter declined linearly with log flash duration, a result attributable to changes in the shape of the function relating persistence to flash duration at lower luminances. The systematic increase for equal-energy stimuli in the duration of the total visual response with increase in flash duration suggests a basis for the recent finding that at threshold equally-detectable stimuli of different durations are discriminable.