dockeray: physical fatigue and mental efficiency. 239 



then indicate that the increased physical fatigue caused by 

 running the longer distance had transmitted to the association 

 centers only relatively small amounts of fatigue products, 

 though the motor system might contain much greater con- 

 centrations. We might, therefore, expect that he would show 

 greater mental fatigue later, or after a greater degree of 

 physical fatigue, than was reached in these experiments. It 

 is doubtful, however, if this theory could be made to account 

 for all the facts. 



That physical fatigue may influence mental efficiency by 

 virtue of its distraction power is evidenced by many little 

 incidents during the course of the experiments and by the 

 introspections of the subjects. In all but the association tests 

 it was possible for the experimenter to mark the record during 

 the course of the test whenever he wished to record any 

 change in the conditions of the experiment. These records 

 could then be checked with the report of the subject at the 

 end of the test. It was found that what the subject reported 

 to be a distraction affected his results in just the same way 

 that it has been found that fatigue may do. Sometimes it 

 caused a decrease in mental efficiency and at other times it 

 caused an increase. Moreover, the results did not always 

 agree with what the subject thought the effect of the dis- 

 turbance had been. In general, a slight noise, such as the 

 peeping of some chicks that were in the room at one time, 

 or a person talking outside near the door, disturbed the sub- 

 ject, but increased his efficiency. On the other hand, louder 

 noises, or longer continued disturbances, were apt to be ac- 

 companied by a decrease in efficiency.* 



It is highly probable that physical fatigue operated as a 

 distraction in much the same way. The accompanying sensa- 

 tion of physical fatigue and the general condition of the sub- 

 jects after physical work may be gathered from their intro- 

 spections. The following are representatives : "Felt shaky 

 in legs, but not sleepy. Mind seemed clear." "Back and feet 

 ached. Did not feel fatigued until about twenty minutes after 

 I stopped physical work." "Could not keep results (multipli- 

 cation) in mind. Arms seemed rigid at the end of the work 



Since the above was written a scries of experiments to study the influence on the 

 sounder test of various forms of distraction has been undertaken by Miss Berger in the 

 Kansas laboratory. So far as the work has progressed the results seem to conform 

 closely to the above casual observations. 



