Temporal Discrimination of Two-Pulse Stimuli as a Function of Psychophysical Method and Luminance

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Abstract
Two experiments extended psychophysical methods of the theory of signal detectability (TSD) to the study of the temporal discrimination of brief two-pulse visual stimuli. Experiment I tested the TSD prediction that observer sensitivity is independent of the psychophysical method used in measurement. Discrimination between a constant-duration (interpulse interval) comparison stimulus (3 ms) and a variable-duration test stimulus (7–32 ms) was measured with a two-alternative forced-choice (FC) procedure and a “yes–no” procedure. Sensitivity was comparable under the two psychophysical procedures, thus supporting the application of TSD in future studies of the sensory processes involved in discrimination of two-pulse stimuli. Experiment II measured discrimination with the FC procedure at three luminance levels: 31.8, 318, and 3183 cd/m2. Discriminability increased with luminance. This significant luminance effect is in agreement with the previous findings of Lewis and Mertens concerning the effect of luminance variation in the photopic range on two-pulse thresholds.

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