THE TIME CONSUMED BY PSYCHOPHYSICAL PROCESSES 675 



pure reflex. The muscular process particularly is facilitated in this way and 

 the reaction is then described as muscular reaction. A reaction in which the 

 attention is strained more especially to receive the impression is called a sen- 

 sory reaction. If the attention be not first aroused, it requires more time also 

 to perceive a stimulus. Thus Wundt found in one experiment with the auditory 

 stimulus that when warning was given the sound was heard in 0.076 second, 

 when not given, in 0.253 second. 



The study of the changes produced in the reaction time by nerve poisons, 

 such as alcohol, coffee and tea, is an important means of learning the physio- 

 logical effects of these substances. 



If instead of a single stimulus, a series of stimuli following each other 

 at a definite interval be given, the reacting person repeats the rhythm to a 

 certain extent independently, and the reaction time sinks to nil. An absolute 

 determination of the time cannot be made under these circumstances: the 

 reaction may take place either at the instant of stimulation, or a little after 

 or even a little before. According to Martius the errors amount to 0.01 

 of a second. 



We very often meet with phenomena of this kind in our everyday life. 

 The playing of an orchestra under the direction of a leader, dancing and 

 marching to music, are all cases in point; likewise the enumeration of heart 

 beats. But if the rhythm of stimuli be not perfectly uniform and the inter- 

 vals not exactly equal, it is impossible to react to them synchronously, and 

 the ordinary reaction time comes into play again. By varying the method of 

 experimentation, we can penetrate still farther into this question of the time 

 consumed by the psychophysical process. The methods employed for this 

 purpose can best be explained by a few concrete examples. 



Suppose the stimulus be applied either to the right or left foot : in the 

 first case the subject is to respond with the right hand, in the second with 

 the left. He has then not only to perceive a stimulus, but to distinguish a 

 definite property and to choose between two movements. On the average the 

 time required for this reaction is, according to de Jeager, 0.066 second longer 

 than the simple reaction time. 



In the case just given the choice was a relatively easy one, because a stimulus 

 on one foot naturally suggests a reaction with the hand of the same side. But 

 if the experiment be so arranged that when a red disk appears the subject is to 

 react with the right hand, and when a blue, with the left, the time is on the 

 average 0.154 second longer than the simple reaction time. The psychophysical 

 processes in this case are of exactly the same kind as the former: the greater 

 interval of time is due to the fact that there is no natural connection between 

 the sense impression and the movement, consequently the choice is more diffi- 

 cult. The time is shorter if a reaction be required for only one of two stimuli. 

 For example, a red or a blue disk may appear: the subject is to react to the 

 latter, but not to the former. The time is then on the average 0.034 second 

 longer than the simple reaction time and thus 0.12 second shorter than in the 

 case last mentioned.. The principle of this method of simple choice is exactly 

 the same as the other: the individual must recognize a definite quality in the 

 stimulus and choose between acting and not acting. But the reason why the 

 choice can be made more quickly is that the attention is concentrated on the par- 



