In 1922 Ives suggested that the fusion of intermittent light sources may be described by means of a Fourier analysis of the visual stimulus. De Lange has recently revived interest in this approach by plotting frequency response curves (“attenuation characteristics”) which relate the amplitude and frequency of the Fourier fundamental of the stimulus at fusion. The resultant functions, while subject to displacement as a function of the intensity and wavelength of the test field, appear to be independent of waveform. One interesting property of this type of analysis is that the direction of analysis with respect to time is irrelevant. Given a train of pulses which consists of three periods of alternating duration, the train ABCABC ⋯ has the same amplitude-frequency components as the train CBACBA⋯. Further, if the three periods are square waves with on times equal to off times, these components remain the same when the on-off times within each period are reversed. The present paper demonstrates that such trains of pulses, having different temporal patterns but the same amplitude-frequency components according to Fourier, have equivalent fusion points.
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