FATIGUE STUDIED IN REACTION TIME EXPERIMENTS

Abstract

The delay in response towards the close of reaction time experiments is evidently due to fatigue affecting some higher central process which is concerned in the maintenance of a close linkage between the central terminations of the sensory tracts and the so‐called voluntary motor centres. This is judged to be the case for the following reasons :—1. An intermittent and prolonged series of auditory stimuli towards which attention does not require to be sharply directed has no distinct fatiguing effect on succeeding reaction time responses for hearing. Hence, one concludes that the delay in response, which occurs after a prolonged series of reaction times (hearing), is not due to a fatigue of the auditory path.2. If, in a series of reaction time experiments, the sensory tracts be changed, as in passing from reaction time (sight) to reaction time (hearing) and then back again to sight, one finds that fatigue is apparently more marked at the close than if the stimulated sensory tracts remained the same throughout. At least, there is no sign of recuperation.As in this case the motor channel remains the same while the higher central one only varies to the extent of being directed towards a different “sensory centre,” the sensory path alone being changed, the fatigue effects must be due to alterations in the higher central links or in the motor path.They are evidently not due to alterations in the last‐mentioned path, as there are no signs of fatigue when this motor path is kept in slight activity of the same type as that existing in reaction time experiments. That is to say, the mere voluntary tapping of the Morse key at the rate of 10 per minute produces no appreciable fatigue.3. The effects of unexpected stimuli are more easily explained on the supposition that the time interval in reaction time is most largely dependent upon the close central linkage.4. The effect of disposition upon the duration of reaction time is most readily understood when one recognises the importance of the central linkage.5. The feelings of fatigue, such as sleepiness, difficulty in keeping the attention fixed, etc., which a person suffers from at the close of a long series, point to a central disturbance affecting the connecting links between sensory and motor channels.