At photopic levels, the amplitude-frequency response curve of the retina assumes a wide variety of shapes when the color of the flickering component of the stimulus is not the same as that of the steady component. Apparently, the photoreaction rates and neural time constants of the various color subchannels differ in the same order as their spectral sensitivities, so that low-frequency sensitivity is enhanced when the adapting wavelength is longer than the flickering wavelength, and high-frequency sensitivity is enhanced when the adapting wavelength is shorter than the flickering wavelength. Chromatically adapted responses to white flicker show that the low-frequency band (4–7 cps) is controlled by the blue-sensitive channel; the middle-frequency band (10–15 cps), by the green-sensitive channel; and the high-frequency band (20–30 cps), by the red-sensitive channel. The results also depend on the spatial pattern of the stimulus; a sharp-edged field obscures the “red” peak and enhances the “blue” peak, even in the absence of blue light. These phenomena cannot be detected with traditional flicker-fusion stimuli, since they do not occur at the CFF.
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