Two-Pulse Measures of Temporal Resolution as a Function of Stimulus Energy*

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Abstract
Mahneke previously reported that increasing the duration of light pulses reduced the two-flash threshold. He attributed this reduction to the increased “quantity of light” provided by the longer light pulses. Two experiments were conducted to test the hypothesis that increased stimulus energy in the photopic range lowers two-pulse measures of temporal resolution. In Experiment I, two-flash thresholds were obtained by increasing either stimulus intensity or stimulus duration over an energy range of 1.4 log units. Comparison of the results obtained from these two manipulations showed that increasing duration reduced two-flash thresholds by 42 msec and 52 msec for two subjects while increasing intensity reduced their thresholds by only 8 and 15 msec. In Experiment II, a change of the stimulus intensity over an even greater range, i.e., 2.4 log units, and use of a more sensitive psychophysical method failed to produce any systematic shift of the two-pulse threshold. It was concluded that for the energy range tested, an increased quantity of light does not modify two-pulse measures of temporal resolution.