September 12, 1890.] 



SCIENCE. 



J43 



Simple Re- 

 actions. 



Adaptive Re-action. 



discussion and the obtained results. If we understand by 



the simple re-action the mei-e signalling that a definite, pre- 



designated, and expected stimulus is present, and by an 



"adaptive" re-action one in which the mode of response 



depends upon and varies with the nature of the stimulus, we 



may distinguish the following stages of connection between 



the two: — 



T. A single stimulus with a single mode of re-action. i 

 II. Several stimuli with a single mode of re-action. 



(a) The sub] ect/orefcnoros the stimulus. | 

 ib) The subject does not foreknow the stimulus. 



III. A single stimulus with several modes of re-action. [ 



IV. Several stimuli with several modes of re-action. j 



(a) The subject foreknows fae stimulus and alec Ihe 

 re-action. 



(6) The subject foreknows the re action, but not the 

 stimulus J 



(c) The subject foreknows neither stimulus 

 nor re-action. 



Or, more simply, if the re-action is foreknown, the pro- 

 cess is a simple re-action ; if not, it is an adaptive re-action. 

 In addition, in the simple re-action the foreknowledge of the 

 stimulus may be entirely definite, the stimulus always being 

 the same, or there may be a known range of variation or an 

 unknown range of variation ; while in the adaptive re-action 

 the possibilities are limited to the latter two. 



I. has been fully considered. In II. (a) we have a num- 

 ber of dilferent simple re-actions; but, instead of investigat- 

 ing them in separate series, we have different kinds in one 

 series; e.g., a sound, a light, or a touch may appear, it being 

 announced to the subject which it is to_ be ; and he in each 

 case re-acts by pressing the key. The impressions may be 

 more homogeneous, as a series of colors; but in all cases the 

 subject need not appreciate the nature of the stimulus, but 

 simply that a stimulus has appeared. In II. (6) the subject 

 knows the possible stimuli, but does not know which is to 

 come next; otherwise the conditions are precisely the same 

 as above. Wundt's experiment with the irregular change 

 between two intensities of sound would belong here, and 

 would indicate that this is an essential factor. In III. the 

 several modes of re action are necessarily known in advance. 

 Instead of testing the different forms of re-actions in separate 

 series, we have several in one series. For example: we re. 

 act to a sound now with the thumb, then with the foreBnger, 

 the subject always knowing in advance what he is to do. In 

 IV. (a) we are combining into one series different forms of 

 simple re-actions, differing both in stimulus and form of re- 

 action: but the complete re-action (e.g., red color to be 

 re-acted to by middle finger) is announced beforehand. In 

 IV. (6) the subject is told in advance how to re-act, but not 

 what the stimulus is to be. However, in both this and the 

 foregoing ease he need not wait to recognize the nature of 

 the stimulus, but reacts as soon as he detects its presence. 

 All these are variations of simple re-action times. When we 

 pass to IV. (c), we have a different, namely, an adaptive, 

 re-action. The subject is not told any thing in advance ex- 

 cept the association upon which he is to react: e.g., if a blue 

 light, with the right hand ; if a red light, with the left hand ; 

 and so on. The essential difference here is that the subject 

 must first distinguish a certain feature of the nature of the 

 stimulus, in this case the color; then call up the appropriate 

 movement and perform it. A re-action of this kind, there- 

 fore, involves a definite distinction of stimuli, and a choice of 

 movements. 



Distinction and Choice. 

 The mental processes involved in an adaptive re-action, 

 in addition to those involved in the simple re action, 

 are thus a more specific recognition of the stimulus, 

 and a choice between movements. By maintaining all 

 other factors alike, the difference of time of the two 

 modes of re-action measures the combined time of distinction 

 and choice. The first determinations of this nature were 

 made by Bonders and his pupils (1865-68'. A simple re- 

 action to a light, white or red, was made in 201(7 (average 

 of five observers) ; ' but an adaptive re-action with the right 

 hand for the one light, and the left hand for the other, in 

 355(T, — a difference of 154(T. Cattell makes a simple adap- 

 tive re-action to two colors in 340(7, his simple re-action time 

 being 146(7, or a difference of 194(7 (XI.). Munsterberg re- 

 acts simply with any of the five fingers in 141(7, but re-acts 

 with a definite finger (according as the numbers of the fin- 

 gers '"one," "two," "three," etc., are called) in 19.5(7 longer 

 (XXIV.). Accepting these as values for the combined dis- 

 tinction and choice time under Simple conditions, our next 

 step would naturally be to determine how much of the time 

 is due to distinction, how much to choice. This is a diffi- 

 cult step; for we cannot readily determine that a distinction 

 has been made, except by indicating it in the mode of re- 

 action, and we cannot execute a choice except upon the basis 

 of some distinction. The mbst usual experiment by which 

 it has been attempted to overcome this difficulty consists in 

 re-acting to only a designated one of a group of stimuli, allow- 

 ing all others to pass without re-action. To take a simple 

 case, let red and blue be the possible stimuli: it red appears, 

 re-act; if blue, do nothing. While this form of experiment 

 is interesting and useful, the inferences from it are not as 

 clear as could be wished. It may be termed the "incomplete 

 adaptive re-action," or briefly the " incomplete re-action." 

 It involves a distinction of the stimulus to be re-acted to, 

 from those not to be re-acted to, and a choice between 

 motion and refraining from action. It seems probable that 

 these processes are respectively easier than a distinction that 

 cannot be anticipated and a choice between two movements; 

 but it seems equally probable that the extent of these differ- 

 ences will vary considerably under different circumstances. 

 If the simple re-action is of the quick, motor form, and the 

 incomplete re-action involves an additional distinction of 

 the stimulus, as well as the choice between motion and rest, 

 the additional time above the simple re-action would be long, 

 and the difference between it and the adaptive re-action 

 short. This is evidently the case with Cattell and Berger, 

 who, with a simple re action of 146(7 and 150(7, perform the 

 incomplete reaction in 306(7 and 277(7, the adaptive in 340(7 

 and 295(7 (IV. and XL). On the other hand, Donders, with 

 an evidently sensory mode of re-action, has a simple re- 

 action of 201(7, an incomplete of 237(7, and an adaptive of 

 284(7. A second method attempts to deal with the difficulty 

 by delaying the re-action until the precise nature of the 

 stimulus has been appreciated, and regards the difference in 

 time between this and the simple re-action as 'he time needed 

 for the distinction of the stimulus. There is nothing but the 

 subjective guaranty that the moment of re-action is coinci- 

 dent with the process of recognition, and we have no reason 

 to regard this guaranty as valid. There may be a tendency 



1 The sign o- indicates one one-thousandth of a second. 



