6i2 THE NERVE CELL. 



down the motor nerves to the voluntary muscle employed for giving 

 the signal ; and, lastly, (9) there is the period of latency of this 

 muscle. 



Attempts have been made to estimate the reaction time in the 

 higher centres, or, in other words, the time taken by the processes (per- 

 ception, apperception, and volition) going on in the nerve cells of the 

 cerebral cortex, by making allowance for each and all the other pro- 

 cesses, and subtracting the sum from the gross reaction time. The 

 resultant would be the time occupied by a psychical act of the simplest 

 kind, and has been termed " reduced reaction time " ; but, considering 

 that many of the above factors are not ascertainable with any degree 

 of accuracy, it is obvious that the mode of its estimation renders the 

 number obtained (0*08 second is given by Exner for a special case) of 

 very little value. A better result might be got by ascertaining the 

 time occupied in performing a movement as a simple reflex, and sub- 

 tracting this from the gross reaction time performed as a voluntary act 

 in response to a stimulus ; it would still be necessary, however, to make 

 an allowance for the time of transmission between the lower and higher 

 level centres. Nevertheless, for want of anything more accurate, we 

 may provisionally accept 0'08 second as the time taken up by a 

 voluntary reaction, i.e. for the block occurring in transmission between 

 the nerve cells of the brain. 



If the psychical process be rendered somewhat more complex than 

 is needed for the performance of a simple voluntary reaction, by the 

 presentation of a dilemma, — e.g., as when the person experimented upon 

 is required to react only when the skin is stimulated at one of two 

 places, or when one of two sounds is heard or pictures seen, — the 

 reaction time is found to be lengthened by from 0*03 to 014 second. 1 

 Or if there is not only the simple dilemma, but also a choice between 

 two modes of response to the signal, it may become lengthened by as 

 much as 0*184 second, according to Wundt (but other observers have 

 not obtained so marked an increase). 2 Or there may be a choice not 

 between two but between several modes of stimulation ; and this, 

 according to the complexity of the psychical process involved, still 

 further lengthens the reaction time. 3 But the differences observed 

 with different individuals become much more marked as the complexity 

 of the psychical process is increased. 



A modification of the ordinary reaction time experiment was employed by 

 Donders, to determine the extra time involved in deciding the path which a 

 voluntary impulse shall take, the person experimented on being stimulated 

 upon one foot, and being called upon to react with the hand of the same side, 

 or to react to a vowel sound by repeating the same sound. The extra time 

 involved over and above the ordinary reaction time for the simple psychical 

 process involved was found in such a case to be about 0*036 second ; this 

 has sometimes been termed the "volitional" time. 4 The introduction of 

 the simplest possible arithmetical process, such as the response to a number 



1 Donders, Arch./. Anat., Physiol, u. wissensch. Med., 1868 ; Wundt, " Elements of 

 Physiological Psychology," vol. ii. Sometimes termed "discrimination time." 



2 E.g. Cattell, Mind, London, 1886, vol. xi. 



a The literature of this subject is given at some length by Richet, " Dictionnaire de 

 physiologic," tome ii. ]>p. 34 to 36. 



4 Cattell found that, although the reaction time is shortened by an increase in the 

 intensity of the stimulus, the volitional time is not affected (Brain, London, 1885, vol. 

 viii. p. 512). 



