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MEMOIRS OF THE IN^ATIONAL ACADEMY OF SCIENCES. 



It follows tliat the length and variability of the reaction-time is the same for J and C, whether 

 the attention be directed to the stimulus or to the movement. In the case of D the time was 

 considerably lengthened when the attention was directed to the raovemeut, he being in the habit 

 of directing his attention to the stimulus. The shorter and more regnlar reactions of J and C 

 are due to the process being more completely reflex, and in this case, as we might expect, the 

 direction of the attention does not alter the times. But it seems that when the reaction is not 

 completely rcHex it may be lengthened by an unusual direction of the attention. Thus D is used 

 to attending to biological details, whereas the observers in Germany may have their mental 

 processes more exclusively accompanied by motor impulses.' 



We next give some experiments in which the nature of the movement was varied. In one set 

 the stimulus was applied alternately to the left and right hands, the reaction being made with the 

 right hand.^ The electrodes were introduced into the knob of the key and the shock applied to 

 the first and second fingers. In this case only one battery was used, the current being divided 

 and passing partly through the induction coil and partly through the chronoscope. Owing to the 

 high resistance in the chronoscope nearly all the current passed through the induction coil. When 

 the current pas.sing through the coil was broken the shock was given, and all the current was 

 simultaneously sent to the electromagnet of the chronoscope and the hands started. This method 

 is convenient, as only one battery is required and the current is sent through the chronoscope at 

 exactly the instant in which the primary circuit of the induction coil is broken. In one set the 

 reactions were made at intervals of about twenty seconds, and measured singly; in the other set 

 they were made in series of ten seconds, the reactions being made at intervals of two seconds, 

 and only the resultant time of ten reactions measured. 



T-4.BLE VII. — Electrical stimulus on left ami on reacting hand. C and J observers. SOO reactions. 



The reaction-time was shorter (for J 21.1 o-, for C 9A a) when the movement was made with 

 the hand to which the shock was api)lied. This might be expected, as the movement is a natural 

 reflex — a person will without reflection withdraw the hand when it touches a hot surface. The 

 fact is of interest in connection with the results noticed above, which show that the cerebral reflex 

 is in general quicker when the sensory fibers stimulated are from the same part of the body as 

 that with which the movement is made. The table further shows that J made the reactions more 

 quickly when ten were made in succession, whereas C made them more quickly when they were 

 made singly. This would have a bearing on the relative times of the two observers in the other 

 tables, but the experiments were not sufficient in number to determine the exact difference. 



We give, lastly, reactions on sound in which the key was released by a movement made, 

 respectively, with the finger, the wrist, the forearm, and the shoulder. 



Table VIII. — Iteaclions on sound; morement with finyer, wrist, forearm, and shoulder. J and C observers. SOO reactions. 



The times show that the reactions were slower when the movement was made from the 

 shoulder, although the muscles concerned are nearer the brain. In the case of J it was also slower 

 with the forearm. The movement with the finger and wrist seems to require about the same time. 



'Results similar to ours bavf been simultaneously obtaiued by Dessoir, Flouruoy, and Baldwin. 

 ' Cf. Exner, Dumreicher and Reicart. 



