The Dependence of Flicker on the Dark-Light Ratio of the Stimulus Cycle

Abstract

The relationship indicated in the title was investigated with reference to the explanation of the fusion point by a process of chemical diffusion within the nervous structures of the retina. The intensity effect was experimentally eliminated by altering the intensity of the light in inverse ratio with the relative duration of the open phase of the cycle, thereby admitting equal quantities of light to the eye per unit time and maintaining its adaptive state at a constant level for all conditions. Incidentally, it was found that the effect of bright surroundings about the intermittent field ran parallel with previous findings of the author and others as to the brightness difference threshold under similar conditions. The general tendency was strong for the fusion frequency to decrease as the light-to-dark ratio increased, average intensity remaining constant. It was found, however, that the resolution of the stimulus intensity cycle into a Fourier series was not useful in interpreting the results: consideration of the first term, or of the first few terms, failed to explain adequately the quantitative variations in fusion frequency that were found. Other difficulties in the way of the diffusion theory are discussed and a feasible method of investigation by means of additive combinations of a few simply related stimulus cycles of pure sinusoidal pattern is suggested.