Abstract

With two electrical analogs of the brightness system it is shown that at a low luminance level (<5 photons) and in the low-frequency region (<2 cps), when under the special visual conditions no attenuation in the system occurs and with a symmetrical luminance variation such as a sinusoidal modulation or a square-wave modulation with a 1:1 on-off ratio, half the crest-to-trough value of the percentage variation at flicker fusion equals the internal threshold value r0; but with an asymmetrical variation such as a square-wave modulation with a 1:3 on-off ratio, it is the crest value of the periodical percentage variation above the mean luminance level which at flicker fusion equals the internal threshold value r0. At high luminance levels an overshoot in the low-frequency region occurs with both forms of square-wave modulation in accordance with the shape of the attenuation characteristic (AC) of the system under the experimental circumstances. At the steep slope of the ACs for the whole luminance range in cone vision, half the crest-to-trough value of the Fourier fundamental percentage variation at the site of the threshold mechanism located anywhere in the system, equals the internal threshold value r0 at flicker fusion.

© 1961 Optical Society of America

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Figures (6)

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Equations (4)

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