Frequency thresholds for two-flash flicker and critical flicker: Why they differ

The minimum interval detectable between two successive flashes is longer than the minimum interval detectable when many flashes are viewed. The probability summation hypothesis is suggested to explain the difference. For a given flash duration, the minimum interval detectable decreases as a function of the number of flashes, n, until n equals about 8 or 10; further increases in n cause no further changes in this interval. Of the total decrease in the interval, from n=2 to n=99, about 90% is explained by the probability summation hypothesis.