With sinusoidal modulation of the radiance of the stimulus as a function of time, amplitude thresholds are measured instead of the repetition-rate thresholds usually obtained in flicker-fusion experiments. Controlling the modulation amplitude independently of the time-average radiance provides an additional degree of freedom, so that the observer’s adaptation level can be held constant while his amplitude sensitivity is measured as a function of the modulation frequency. With an “edgeless” flickering field, these amplitude sensitivity curves show a broad peak of maximum visual response, in the region from 10 to 20 cps at high photopic levels. Such classic relationships as the Ferry-Porter, Talbot-Plateau, and Weber-Fechner laws are derivable from the present results, as descriptions of the behavior of certain parts of the amplitude sensitivity curves as functions of adaptation level.
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