114 



SCIENCE. 



[Vol. XVI. No. 395 



tongue in 182ff, though other subjects require about SOOff. 

 On the back of the tongue the time is much longer, and it 

 varies for different tastes, being longest for bitter, shortest 

 for salt, and about equal for sweet and sour. Within the 

 same sense the re-action time will vary according to the na- 

 ture and place of the stimulus. The above cited differences 

 for tastes and smells show this; and for different visual im- 

 pressions, for different tones, for contact at different parts of 

 the body, different results have been obtained, referable to 

 slight variations in sensibility, length of nerve traversed, 

 clearness of the impression, and the like. These minor dif- 

 ferences are not easily established, but the following may be 

 cited. Exner re-acts to an electric shock on the hand in 

 . 132(T, on the forehead in 137(7, on the foot in 175 ff; v. Wit- 

 tich re-acts to a point on the back of the finger in a longer 

 time than to one on the front, 1440' and 156 (T, and regards 

 the difference as due to a difference of sensibility. Hall 

 and Kries clearly show that the re-action to a point looked 

 at in indirect vision is longer than to one in direct vision, 

 195(7 and 2350", and find further differences according as the 

 point is above or below, inside or outside, the retinal centre. 

 A high tone is re-acted to more quickly than a low one, and 

 so on. 



It is easier to demonstrate the influence of (2) the inten- 

 sity of the stimulus. Within limits, intense stimuli affect 

 sense-organs more quickly than weak ones, and, roughly 

 speaking, an increase in the intensity of the stimulus is con- 

 comitant with a decrease in the re-action time. According 

 to Wundt, the noise of a hammer falling respectively from 

 heights of 1, 4, 8, and 16 millimetres was re-acted to in 217(T, 

 146(T, 132(T, and 135(7, and the sound of a hall falling from 

 heights of 2, 5, 25, and 55 centimetres in 1760', 161(7, 159(7, 

 and 94(7 respectively. Exner varied the length and there- 

 fore the brilliancy of an electric spark from 0.5 to 7 milli- 

 metres and obtained a steadily decreasing re-action time of 

 158(7 to 123(7. More complete are the observations of Ber- 

 ger and Cattell, who found that as the light increased from 

 7 to 23, to 123, to 315, to 1.000, and to two greater but not 

 determinable degrees of intensity (as compared with a small 

 unit of light), the re-action times fell (average of two ob- 

 servers) from 210(7 to 184(7, to 174(7, to 170(7, to 169(7, to 

 156(7, to 148(7. For sound, as the ball fell from heights of 

 60, 160, 300, and 560 millimetres the re-action times were 

 151c7, 146(7, 127(7, and 123(7. For electrical touch excitations, 

 re-actious to four grades of stimuli separated by equally 

 perceptible differences were made (average of two observers) 

 in 173(7, 159(7, 145(7, and 145(r. Wundt regards the differ- 

 ence in re-action times of the different senses as in part 

 referable to differences in intensity, and, when re-acting to 

 just perceptible intensities of sensation in various senses, 

 finds about the same long time for each, 330(7. 



3. The Mode of Re-action. The various movements by 

 which we may signal that a sensation has been received may 

 differ in the ease of their execution, in the length of nerve 

 traversed, as well as in the naturalness of association with 

 the impression. Such differences, however, seem to be 

 small; when once the movement is understood and antici- 

 pated, the difference in the times of its execution is slight. 

 Thus, MCinsterberg found, in testing the re-action of each of 

 the five fingers, that while at first the thumb and little finger 

 re-acted more slowly than the others, after some practice the 



times of all were substantially the same. Fere, however, 

 has some results suggesting that the fingers making the 

 strongest movements re-act in the shortest times. Very in- 

 teresting, too, is the experiment of Ewald in which the 

 stimulus, an electric shock, is given to the finger in the very • 

 key by which the re-action is signalled, the re-action consist- 

 ing in the very natural movement of drawing the finger 

 away. Under these circumstances he found a brief and 

 constant time of 90(7. Both Vintschgau and Cattell have 

 compared the time of re-acting by closing a key with the 

 finger and by speaking a word, and find the vocal method 

 the longer by about 16(7 and 30(7 respectively. Differences 

 in re-acting from the two sides of the body have been ob- 

 served by some, the right side showing the shorter re-action, 

 but this difference can hardly be considered as constant. 

 Orchansky has shown in one case that the movements of 

 inhibition take about the same time as those of excitation of 

 a muscle, and it would be possible to study the relative ease 

 of various movements by this method. A practical example 

 is furnished by the commands of military drill, the words, 

 "carry," ''present," etc., announcing the mode of re-action 

 for the performance of which the following word, " arms," 

 is the signal. 



(B) We pass next to the more important subjective fac- 

 tors, referring in the main to the expectation and the atten- 

 tion. While nothing has been definitely said upon this 

 point, the implication has been that the subject tries his ut- 

 most to re-act as quickly as possible, and that he knows the 

 nature of the experiment. While the influences now to 

 be discussed seem to be general in their effect, making the 

 nervous system at one time a better and again a worse re- 

 acting apparatus, they may, in certain respects, be subjected 

 to a more definite analysis. We begin with (1) the subjecfs 

 fore-knowledge of what is to take place. We may antici- 

 pate the outcome of experimentation on this point by for- 

 mulating the law that the more definite the fore-knowledge 

 of the subject the quicker the re-action. Apparently there 

 is a process that must be gone through with in each re action, 

 and the better prepared the subject is for this, — that is, the 

 more of this process gone through with before the giving of 

 the stimulus, — the less of it falls within the measured inter- 

 val. The precise nature of this process is a difficult and 

 much discussed problem. It may be sufficient to note at 

 present that the re action to a certain stimulus cannot hut 

 imply in some sense the distinction of that stimulus from the 

 many others by which we are constantly surrounded. If 

 the subject be re-acting to a visual impression, he will prob. 

 ably not press the key should a noise occur in the room or 

 something accidentally come in contact with his hand. To 

 re-act to a visual impression thus implies the distinction of 

 that from other impressions. It implies the identification 

 of the expected with the existing impression. Just as we 

 recognize an appearance in the heavens or under the micro- 

 scope more readily when we know where and what to look 

 for, or as we immediately recognize an almost forgotten ac- 

 quaintance when expecting him, though at a chance meeting 

 we might have passed him without recognition, so we re-act 

 to an impression most quickly when it is most definitely ex- 

 pected, with regard to its nature, its time and place of ap- 

 pearance, and the like. This expectation may be more or 

 less specific, and an interesting series of experiments consist 



