Fig. 49.
Simple Reactions.—It is found that the reaction-time differs in the same person according to the direction of his expectant attention. If he thinks as little as possible of the movement which he is to make, and concentrates his mind upon the signal to be received, it is longer; if, on the contrary, he bends his mind exclusively upon the muscular response, it is shorter. Lange, who first noticed this fact when working in Wundt's laboratory, found his own 'muscular' reaction-time to average 0´´.123, whilst his 'sensorial' reaction-time averaged as much as 0´´.230. It is obvious that experiments, to have any comparative value, must always be made according to the 'muscular' method, which reduces the figure to its minimum and makes it more constant. In general it lies between one and two tenths of a second. It seems to me that under these circumstances the reaction is essentially a reflex act. The preliminary making-ready of the muscles for the movement means the excitement of the paths of discharge to a point just short of actual discharge before the signal comes in. In other words, it means the temporary formation of a real 'reflex-arc' in the centres, through which the incoming current instantly can pour out again. But when, on the other hand, the expectant attention is exclusively addressed to the signal, the excitement of the motor tracts can only begin after this latter has come in, and under this condition the reaction takes more time. In the hair-trigger condition in which we stand when making reactions by the 'muscular' method, we sometimes respond to a wrong signal, especially if it be of the same kind with the one we expect. The signal is but the spark which touches off a train already laid. There is no thought in the matter; the hand jerks by an involuntary start.
These experiments are thus in no sense measurements of the swiftness of thought. Only when we complicate them is there a chance for anything like an intellectual operation to occur. They may be complicated in various ways. The reaction may be withheld until the signal has consciously awakened a distinct idea (Wundt's discrimination-time, association-time), and may then be performed. Or there may be a variety of possible signals, each with a different reaction assigned to it, and the reacter may be uncertain which one he is about to receive. The reaction would then hardly seem to occur without a preliminary recognition and choice. Even here, however, the discrimination and choice are widely different from the intellectual operations of which we are ordinarily conscious under those names. Meanwhile the simple reaction-time remains as the starting point of all these superinduced complications, and its own variations must be briefly passed in review.
The reaction-time varies with the individual and his age. Old and uncultivated people have it long (nearly a second, in an old pauper observed by Exner). Children have it long (half a second, according to Herzen).
Practice shortens it to a quantity which is for each individual a minimum beyond which no farther reduction can be made. The aforesaid old pauper's time was, after much practice, reduced to 0.1866 sec.
Fatigue lengthens it, and concentration of attention shortens it. The nature of the signal makes it vary. I here bring together the averages which have been obtained by some observers:
| Hirsch. | Hankel. | Exner. | Wundt. | |
| Sound | 0.149 | 0.1505 | 0.1360 | 0.167 |
| Light | 0.200 | 0.2246 | 0.1506 | 0.222 |
| Touch | 0.182 | 0.1546 | 0.1337 | 0.213 |
It will be observed that sound is more promptly reacted on than either sight or touch. Taste and smell are slower than either. The intensity of the signal makes a difference. The intenser the stimulus the shorter the time. Herzen compared the reaction from a corn on the toe with that from the skin of the hand of the same subject. The two places were stimulated simultaneously, and the subject tried to react simultaneously with both hand and foot, but the foot always went quickest. When the sound skin of the foot was touched instead of the corn, it was the hand which always reacted first. Intoxicants on the whole lengthen the time, but much depends on the dose.
Complicated Reactions.—These occur when some kind of intellectual operation accompanies the reaction. The rational place in which to report of them would be under the head of the various intellectual operations concerned. But certain persons prefer to see all these measurements bunched together regardless of context; so, to meet their views, I give the complicated reactions here.
When we have to think before reacting it is obvious that there is no definite reaction-time of which we can talk—it all depends on how long we think. The only times we can measure are the minimum times of certain determinate and very simple intellectual operations. The time required for discrimination has thus been made a subject of experimental measurement. Wundt calls it Unterscheidungszeit. His subjects (whose simple reaction-time had previously been determined) were required to make a movement, always the same, the instant they discerned which of two or more signals they received. The excess of time occupied by these reactions over the simple reaction-time, in which only one signal was used and known in advance, measured, according to Wundt, the time required for the act of discrimination. It was found longer when four different signals were irregularly used than when only two were used. When two were used (the signals being the sudden appearance of a black or of a white object), the average times of three observers were respectively (in seconds)