FUNCTIONS OF THE CEREBRAL HEMISPHERES 519 



complicate the dilemma to almost any extent. Thus the experiment 

 may be so arranged that either a red or a white disc appears and the 

 subject has to react with the right hand to the red disc and with the 

 left hand to the white disc. In such an experiment the reaction time 

 was found to be 0-154 sec. longer than the simple reaction time. A 

 still more complex process would be involved in the experiment in 

 which a word was spoken, and the subject had to speak some other 

 word which had some association with the word which formed the 

 stimulus, e.g. horse mammal ; paper pen, &c. In such an experi- 

 ment the reaction time was found to be as long as 0-7 to 0'8 sec. 



We see that the recording of the time of occurrence of any physical 

 event can only occur after a certain lost time, which represents the 

 observer's reaction time for the stimulus in question. This only 

 applies, however, to movements carried out in response to single 

 stimuli, or to stimuli repeated at irregular intervals. When the 

 stimuli are rhythmic the lost time only applies to the first one or 

 two of the stimuli. The observer or subject is conscious of the 

 interval elapsing between the physical event and his reaction, and 

 anticipates the later stimuli so that his reaction becomes synchronous 

 with the stimulus. This synchronism of stimulus and reaction 

 characterises all rhythmic movements, such as dancing or the playing 

 of an orchestra in time with the beat of the conductor's baton. 



