Bauhaus-Universität Weimar

On reaction-times and the velocity of the nervous impulse
Cattell, J. McKeen and Dolley
a discharge from a motor center; (G) the motor impulse travels along motor tracts in the brain; (7) 
along the motor nerve and, it may be, spinal cord, and, finally, (8) the muscle is innervated. The 
process is probably an acquired cerebral reflex, not accompanied by consciousness. The stimulus 
is indeed perceived, but probably not before the motor impulse has been discharged. The 
stimulus causes two sorts of cerebral changes, the discharge of the motor impulse, and changes in 
the cortex, which are accompanied by consciousness. But, contrary to the views of most physi¬ 
ologists, we think the movement does not follow on changes in consciousness, but is simultaneous 
with or actually prior to them. What volition is concerned in the process precedes the reaction 
and consists in preparing the motor impulse, which is reflexly discharged.1 
The conditions on which the duration of the reaction depends are partly such as relate to the 
subject reacting and partly such as relate to the stimulus. Some subjects react more quickly than 
others, and this difference in time must represent real differences in the nervous system. The 
personal difference in reacting has not yet been adequately investigated.2 Observations which we 
have made indicate that the reaction-time is shorter for women than for men, and for Americans 
than for Germans. The reaction-time is said to be longer in childhood and in old age. We have, 
however, found a normally short reaction in a child of 3 and an unusually short and regular 
reaction in a man of 65. We have found the reaction-time to be lengthened in certain diseases of 
the nervous system, and the test (especially in unilateral diseases in which the reacting hand or 
foot and the point of application may be varied) might prove useful in diagnosis, more especially 
in indicating progression or recovery. We have found the times of mental processes such as 
perception, volition, memory, association, etc., to vary more in different individuals than the times 
of the simple reaction, and these may prove useful not only in diagnosis of disease, but in scientific 
pedagogy and in directing the ordinary conduct of life. Our experiments on personal differences 
are not completed, and will not be treated in this paper. 
In the same individual the duration of the reaction time and of mental processes differs at 
different times. Owing, however, to the reflex nature of the reaction its length is not greatly 
affected by the condition of the observer, the time of day, the number of reactions already made, 
nor the amount of practice. These factors, and especially the effects of attention, we shall consider 
in view of our own residts. It may here be stated that in our experiments the mean variation 
of a reaction from the series to which it belongs was usually less than 0.01 second, and the mean 
variation of series made on different days was also usually less than 0.01 second. 
The length of the reaction-time is clearly influenced by the nature of the stimulus and the 
point of its application. The reaction-time is about 0.025 second longer for light than for sound 
and touch. This may be due to the greater time required for converting the physical motion into 
a nervous impulse in the retina, where a chemical process is supposed to take place. It may also 
be due to the cerebral reflex being less perfect, reflex and automatic movements being made more 
readily in answer to sounds and touches than to lights. We have found the reaction on touch 
shorter than on electric stimulation. The reaction-time becomes shorter as the intensity of the 
stimulus is increased, though the difference is not great except in the case of very weak stimuli. 
The- area of the stimulus probably only affects the length of reaction in so far as it alters the 
intensity. The quality of stimuli of the same intensity (e. g., different colors or noises) does not 
appreciably affect the length of the reaction. 
1 It is not necessary to repeat in this place references to the somewhat extended literature on reaction-time and 
the velocity of the nervous impulse; cf. for these Hermann, in his Handbuch der Physiologie, Vol. II, and Exner, in 
the same work, Vol. Ill, Leipzig, 1879; Wundt, Grundziige der physiologischen Psychologie, 4th edition, Leipzig, 
1893; Cattell, Philosophische Studien, Vol. Ill, and Mind, Vol. XI, 1886; Dumreicher, Zur Messung der Reactionszeit, 
Dissertation, Strassburg, 1889; Jastrow, The Time Relations of Mental Phenomena, New York, 1890, and the 
Catalogue of the Surgeon-General’s Library. 
2 It is, indeed, the case that the whole question of reaction-time lias had its origin in the personal equation of the 
astronomer. But the problems, though often confused, are quite distinct. The astronomer watches the star as it 
crosses the field of his telescope and records as nearly as he can the instant at which it passes the central thread. 
In such a case a reaction may perhaps be said to take place, but the personal equation of the astronomer depends 
not on the duration of the reaction hut on the time at which the process is initiated, and may be as great as one 
second. It seems likely that the astronomer could greatly reduce his personal equation by adopting the methods of 
the psychologist. If the star passed behind a screen and emerged as it passed the meridian, the observer could not 
have a negative personal equation, and the probable error of a single observation might be reduced to 0.01 second.


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