Abstract: Three groups of railway workers consisting of 5 key punch operators, 9 calculators and 36 dispatchers were tested on C. F. F. at different times while on duty. It is found that the fusion frequency is highest for the punch operators and calculators before work, then it decreases gradually as they proceed in their work. The fusion frequency increases slightly after each short break at two hour intervals, but never reaches the level as high as the initial values. There is no detectable change in fusion frequency for the dispatchers on day shift; but there is marked decrease after night shift. It is concluded from this study that the fusion frequency of flicker may be used to test the degree of fatigue of the central nervous system.

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