The threshold visibility of uniformly moving colored gratings was investigated. The gratings were equiluminous sine-wave patterns, generated on a color-television display. The traveling waves were detected by the subject over a range of three log units of background illuminance, including various spatial- and temporal-frequency combinations. The experiments indicate that no resonance phenomena occur in the spatiotemporal color-discrimination system of the eye. This system probably functions as a low-pass filter. The color coding takes place in much narrower frequency bands than the brightness coding. A regular motion of the pattern never enhances the visibility of the color gratings. The temporal characteristics of the chromatic-discrimination system show very much resemblance to its spatial qualities. Our experiments show that the threshold chromatic contrast is proportional to the square root of the illuminance. This fundamental relationship can easily be understood from the statistical properties of the photons, absorbed in the differential receptor systems.
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