The course of dark adaptation was followed after pre-exposure to both intermittent and continuous light. The variable under investigation was the influence of the light-dark ratio of the intermittent pre-exposure. The rate of intermittence was 1 cycle/second and four light-dark ratios were used: 1/2–1/2, 1/4–3/4, 1/8–7/8, and 1/16–15/16. The intensities of pre-exposure were: 8860, 886, and 88.6 mL. At the lowest intensity no differences were found between any of the intermittent and their continuous control pre-exposures. At the two higher intensities the curves for the intermittent procedures were different from the control procedures and the differences were related to the light-dark ratios. It was found that, on the whole, the shorter the amount of light-time in the ratio the lower was the initial dark adaptation threshold, the greater the difference between the experimental and control curves throughout the course of dark adaptation, and the shorter the time elapsing before the appearance of the first colorless (rod) threshold stimulus.
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