We have measured the sensitivity of the visual system to temporal modulation with unpredictable, aperiodic signals. We used three kinds of stimulation, (i) a band-limited gaussian random signal, (ii) a passband-limited gaussian random signal, (iii) a periodically quenched random signal. The sensitivity to stimulation with random signals can be predicted from the sensitivity of the visual system to periodic temporal signals. The sensitivity to random signals with narrow frequency bands at high frequencies is governed by the pseudoflash phenomenon. If the bandwidth is such that the signal contains less than two independent samples per second, the psychometric curve follows from the amplitude distribution of the random signal. If the signal contains a larger number of independent samples per second, the psychometric curves are as steep as they are for sine-wave stimulation. If the De Lange characteristic is the envelope of the sensitivity characteristics of independent channels, sensitive to specific frequency bands, then these experiments permit us to estimate the bandwidth of the most-sensitive channel.
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