ferent nervous conduction. It was found, however, that the method was not suited to the problem. The experiment was then transferred, as a quantitative experiment, to the psychological laboratory, and was employed, in various forms, to measure the duration of certain mental processes. But psychology knew so little of the mental pro- cesses comprised within the reaction time, that the assignment § 121. The Reaction Experiment of duration was altogether speculative. And so the experiment has now come to be, in essentials, a qualitative experiment. It allows us to repeat, over and over again, a particular type of con- sciousness; it allows us to vary this type, in manifold ways, and still to repeat our ob- servations as often as is necessary to their complete analysis; it thus affords an admi- rable control of intro- spection. The reac- Fig. 63. Wundt's Sound Hammer, often used as stimulator in the reaction experiment. The wires of the chronoscope circuit are led to the posts i, 2; the posts 3, 4 of the electro-magnet are in connection with a separate battery and key.
tion times are then valuable, not in themselves, but as checks upon the observer. If the times of simple reaction to light are, for two normal observers and under the same conditions, 290 cr and 180 a respectively, it is clear that we are dealing with different con- sciousnesses; the observers are not doing the same thing. To find out, by variation of conditions, precisely what they have been doing is a psychological problem of considerable impor- tance. — The technique of the reaction experiment is described in the manuals of laboratory practice, and need not here be repeated. The necessary instruments are a stimulator, a reaction key, and some form of time-measuring apparatus. Stimulators have been devised which set up a sensation in the various departments of sense, which exhibit more complex stimuli (words, geometrical FIG. 64. Finger Key, modelled upon the ordinary telegraph key: commonly used as break-key in the reaction experiment.
Action figures), and which give a succession of varying stimuli (colours, noises of different intensity). Keys have been constructed for movements of the finger, foot, lips, throat, eyelid, and for selec- tive responses, e.g., for movement for any one of the ten fingers. The time-measuring apparatus ranges from the stop-watch, whose unit is \ sec, through instruments of increasing accuracy, up to the electrical chronoscope, whose unit is i a-.
§ 122. The Analysis of the Simple Reaction. — In 1887 and 1888, two investigators made the independent discovery that the length of the simple reaction time differs, according as the attention of the reactor is directed to the stimulus which is to release the reaction movement, or to that move- ment itself. Since the latter date, it has been customary to distinguish three types of simple reaction: the sensory, the muscular, and the mixed, — this last representing the nat- ural attitude of a reacton whose attention is fixed prepon- derantly neither upon sensory stimulus nor upon movement of response, but is either distributed more or less evenly to both, or turns in quick succession from the one to the other.
The approximate times for the two extreme modes of reaction are as follows (time-unit = 1 <r): — Muscular Sensory Light Electrical cutaneous stimulus.
2IO The range of variation (p. 211) is, for moderately practised reac- tors, about y1^ of the total sensory time, and about y^ of the total muscular time. The times for warmth and cold are largely depend- ent upon the conditions of the experiment. We may say, however, that on a rough average those for warmth approximate the times § 122. The Analysis of the Simple Reaction 433 for light, and those for cold the times for sound. The times for taste, smell and pain have not yet been standardised. The times of the mixed reaction lie between those of the extreme forms, tending to be longer or shorter according as the predisposition of the observer or the circumstances of the experiment tip the scale of attention on the side of stimulus or of movement.
The distinction of the three types of reaction is valid. But analysis has shown that the phrase ' direction of attention ' is ambiguous. The course of consciousness depends entirely upon the attitude which the reactor takes to the experiment; and this attitude depends upon his understanding of the instruction given by the experimenter. Evidently, then, the instruction must be clear-cut; it must limit and restrict as well as positively command. If I say to the reactor: ' React as soon as you see the white card; keep your attention, all through, upon the card; never mind about the movement, but let that follow of itself ' — if I say this, I have given instruction for the sensory type of reaction. Nevertheless, the instruction is am- biguous. For the words ' as soon as ' have suggested to the reactor that he is to react as quickly as possible; and if he reacts as quickly as possible, he will tend to slur the perception of the white card, and to react upon the least perceptive cue. As the experiments proceed, he will tend, also, to prepare more and more completely for the responsive movement: and so, simply through the fault of instruction, he will shift from the sensory to the muscular form of reaction. If, again, I say to the reactor: ' React as soon as you see the white card; but keep your atten- tion, all through, upon the movement,' my instruction is ambiguous in the opposite way. The words ' as soon as ' suggest that the reaction is to follow as quickly as possible 9?
434 Action upon the appearance of the stimulus, but the phrase ' attend to the movement ' may negative that suggestion; the reactor, instead of getting the movement ready, may try to hold it clearly in consciousness, and so the response may be delayed.
It follows that the instruction must be very carefully worded; it must be brief, in order that it may be grasped as a whole; yet it must be explicit, both as to what the reactor is to do and as to what he is not to do. Moreover, it must be repeated, over and over, as the experiment proceeds, in order that the mode of reaction may not change, without the reactor's knowledge or intention, from one type to another.
The reaction experiment, as a psychological unit, may be divided into three periods: the fore-period, extending from the preliminary, signal to the exhibition of the stimulus; the mid- period, extending from the appearance of the stimulus to the performance of the reaction movement; and the after-period, following upon the movement, during which the reactor makes his introspective report. The fore-period is dominated by the instruction, which may come to consciousness in very various ways. Our analyses are still far from complete; we must often be content, as in the description of memory and imagination, barely to indicate some elusive and time-worn process, whose observation demands special conditions; but the following account will suffice for a general understanding of the reaction conscious- ness.
We begin with the muscular reaction. In its extremest form, the instructions are represented, simply and solely, by kinaes- thetic (principally strain) sensations in the reacting member (prin- cipally in the finger). These sensations appear as a contextual complex, which carries the meaning ' You are to react as quickly as possible '; they have been termed, accordingly, ' sensations of intended movement.' This restriction of consciousness, to the § 122. The Analysis of the Simple Reaction 435 apprehension of the stimulator and a kinaesthetic context, is rare. In the typical form of the muscular reaction, the sensations of intended movement are again prominent. But there are also present a conscious reference to the expected stimulus (carried by fixation of the stimulator), and a conscious connection of the expected stimulus with the intended movement. In another form, the kinaesthetic sensations are replaced by some imaginal process: a visual image of the moving finger, the word 'movement' in internal speech; while there is still a conscious reference to the expected stimulus. In a fourth form, kinaesthetic sensations and internal speech are both in evidence, but the reference to the expected stimulus may be so clear as to approximate the sensory type. Lastly, the kinaesthetic sensations and the reference to stimulus may be accompanied by ' as quickly as possible ' in inter- nal speech: the reactor intends to make the movement, as nearly as he can, simultaneous with the appearance of the stimulus. In the extremest form of the sensory reaction, the instructions are represented, simply and solely, by the expectation (without image) of the coming stimulus. This restriction of consciousness, to the apprehension of the stimulator and an expectation context, is rare. In the typical form of the reaction, expectation of stimulus is combined with a conscious reference to the intended movement; there are, however, no sensations of intended move- ment. In another form, the expectation takes imaginal shape as a visual image of the stimulus, or ' now it's coming ' in internal speech. The conscious reference to the intended movement is again present, but there are still no sensations of intended move- ment. In a fourth form, the expectation and the conscious refer- ence are accompanied by kinaesthetic sensations in the reacting member, around the eyes, etc.; here is an approximation to the muscular type. Lastly, the expectation and the reference may be given together with ' as quickly as possible ' in internal speech: the reactor intends to make the movement, as nearly as he can, simultaneous with the appearance of the stimulus. Sometimes this temporal set is represented by the visual image, e.g., of a swinging pendulum.
436 Action Both kinds of instruction may, on occasion, set up conscious- nesses of the pattern which they are designed to prevent: the muscular instruction may prompt to a sensory preparation, the sensory to a muscular. So flagrant a miscarriage of instruction is, of course, rare; that it occurs at all is sufficient proof of ambi- guity. Since, in fact, it is not a simple ' direction of attention ' that differentiates the reactions, but the reactor's attitude as conditioned on instruction, we may drop the names ' sensory' and ' muscular' al- together, and substitute for them the purely descriptive terms 'com- plete ' and ' abbreviated.' The correct instruction for the abbreviated form would then run somewhat in this way: ' You will see a white card; react as soon as you see it; react as quickly as possible.' For the complete form: ' You will see a white card; react when you see it; do not react till you see it clearly.' And for the natural form: ' You will see a white card; react when you see it.' The first instruction definitely suggests the preparation of the responsive movement; the second as definitely suggests the clear perception of the stimulus, while it heads off the auto-sugges- tion that the movement is to be made as quickly as possible; the third leaves the reactor to his own devices.
When the course of consciousness has once been deter- mined, by the reactor's acceptance of the instruction, the experiment proceeds smoothly to its conclusion. It has been suggested that the sensory reaction breaks apart; that, after the apprehension of stimulus, there is a distinct conscious impulse to move the finger; whereas, in the muscular reaction, the movement follows directly upon the perception. Introspection shows, however, that this sundering of the reaction consciousness occurs, if at all, only in the earliest stage of practice; as a rule, the finger moves as directly in the sensory as it moves in the muscu- lar type of experiment. The difference between the two reactions is rather this: that, in the sensory, the stimulus is apprehended in its proper quality, as ' something white,' and that, in the muscular, it is apprehended merely as a visual stimulus of indeterminate quality or, still more baldly, as ' something different.' The physiological condi- tions of this difference can only be guessed at.
The reinstatement, in the few minutes of the after-period, of the consciousness of the two preceding periods, has been ascribed to the operation of perseverative tendencies. We have seen, how- ever, that the assumption of these tendencies is unnecessary The simple reaction experiment can be varied in many ways. Thus, we may investigate the influence of intensity and quality of stimulus, of variation of the time allowed for accommodation of attention, of the omission of a preliminary signal, of the presence of distracting stimuli, of fatigue, of drugs. Unfortunately, the main emphasis in all this work has been laid upon the time of reaction. Since we have temporal norms for the three most accessible sense- departments (p. 432), and since our psychological analysis of the sensory and muscular reactions affords a general survey of the reaction consciousness, it is possible, by comparison of results, to estimate the effect of the changed conditions and also to trace, with some degree of probability, the changes in consciousness itself. Here as everywhere, however, we are bound, sooner or later, to face the psychological problem in detail, to push our special analyses to the bitter end. For the past two thousand years, psy- chology has been resting upon plausibilities and probabilities. Now that we are beginning tc have a psychology of facts, it is both honesty and policy to state where the facts end and where specu- lative construction begins.
§123. Compound Reactions. — The simple reaction ex- periment may be most easily complicated by substituting for the single stimulus a number of similar stimuli. The reactor is told, for instance, that he will be shown either a black or a white card, and that he is to react when he has apprehended the white as white or the black as black; he 438 Action does not know which of the two qualities will be presented in any given experiment. Or he may be told that he will be shown a black, white, grey, or coloured card, and that he is to react when he has apprehended the particular stimulus in its proper quality. The first of these is termed, technically, the discriminative reaction, on the ground that the reactor discriminates between the two known stimuli. The second is known as the cognitive reaction, on the ground that the reactor directly apprehends — cognises rather than recognises — the quality of the unknown stim- ulus. In fact, however, the reactor's attitude, under the two forms of instruction, is essentially the same.
In the fore-period of the discriminative reaction, the reactor's consciousness consists, primarily, of the perception of the stimula- tor and of the intention to wait, to give the stimulus full time. Sometimes the names of the stimuli ' black, white ' appear in in- ternal speech; sometimes the intention is itself carried in verbal terms, — 'black, white; make sure; react.' In the mid-period, the clear apprehension of the stimulus may be attended by a feel- ing of assent or acknowledgment, as well as by the assurance that the finger may now be moved; or the two processes may run to- gether, as the assurance that this is the thing that was expected and that was to be reacted upon: movement then follows at once.
In the fore-period of the cognitive reaction, consciousness again consists, primarily, of the perception of the stimulator and the intention to give the stimulus full time; sometimes, however, there is diffused strain about the eyes and the upper part of the body, and a repetition of the instruction in internal speech, — ' grey, colour; react quickly.' In the mid-period, the clear ap- prehension of the stimulus may bring with it the feeling of assent, with or without the specific name of the light or colour in inter- nal speech; or a stimulus may be apprehended — in the precise terms of the instruction — as.'coloured'; or, again, it may be ap- prehended as the thing to react uoon; or, finally, towards the end of a series, as that familiar thing. Here, as in the discriminative reaction, movement follows at once upon this complex apprehen- sion. The two modes of reaction may evidently be bracketed together.
Another method of complicating the simple reaction ex- periment is to vary the responsive movement. Thus, the reactor is told that he will be shown either black or white, and that he is to react only when he has apprehended the black as black or the white as white. So far the instruction is the same at that for the discriminative reaction. But further, he is to react to black by a movement of the right hand, and to white by a movement of the left hand. Or, he is to react to black by a movement of the right hand, but is not to react to white at all.
Once more: the reactor is told that he will be shown a light or a colour, and that he is to react only when he has apprehended its specific quality. So far, the instruction is the same as that for the cognitive reaction. But further, he is to react by naming the perception: that is, the re- sponsive movement is to be different for every stimulus. Or, he is to react to the colours by naming them, but is not to react to the lights at all.
All these forms are termed, technically, choice reactions, on the ground that the reactor is called upon to make a choice, either between two different movements, or between movement and quiescence. In fact, however, the observer's attitude, under the two forms of instruction, may be widely different, and it is more than doubtful if either instruction arouses the process of choice.
It is, again, unfortunate that investigators have so far been con- cerned rather with the recording of times than with an analysis of 44° Action the reaction consciousness. The times themselves have been ob- tained under varying experimental conditions, so that their norms cannot be stated. The analytical material is very scanty.
In a series of cognitive choice reactions (white to be reacted upon, other stimuli to be disregarded), the fore-period opened with the words ' react to white; make sure ' or ' right away; react to white ' in internal speech; the word ' white ' carried the mean- ing ' white and nothing else.' Later, the fixation of the stimulator set up intensive strains about the eyes, and the instruction was present to consciousness only as a general intention. If the white stimulus appeared, the mid-period showed a brief pause, culminat- ing in the reactor's assurance that ' that's what I was waiting for,' or ' that's white all right,' whereupon the reaction movement fol- lowed at once. If some other stimulus appeared, its apprehen- sion might connect directly with the assurance that it was not to be reacted upon; then the reactor took it quite quietly. Or — if the card was a printed card, with a white ground — sensations of in- tended movement might arise at the first glimpse of white, to be inhibited later, by a stronger pressure on the key, when the letters came into view.
In a series of discriminative choice reactions (visual or auditory presentation of vowels or consonants, each one of which is corre- lated with movement of a particular finger), the fore-period showed two main forms of conscious preparation, the sensory and the associative. The purely sensory preparation consists in attentive perception of the stimulator, with definitely directed (but image- less) expectation. This simple disposition of consciousness may be complicated either by sensations of intended movement in arms and fingers, or by the appearance of a complex visual image, a sort of monogram of the letters used as stimuli. If the reactor has not already practised the correlation, his preparation is associa- tive: there is repetition of the instructions in internal speech, ' E right, O left.' Consciousness may again be complicated, either by visual images, or by sensations of intended movement. It is noteworthy that these kinaesthetic sensations may appear, with the meaning 'right' and 'left,' not only in the corresponding arm and fingers, but also about the eyes. We have seen that they do not necessarily lead to movement; we now find that they are not con- fined to the reacting member. They are, of course, the sensations which have often been described as sensations of innervation (§ 49 ).
In the mid-period, the unpractised observer first apprehends the stimulus, then repeats the fitting instruction (' right,' ' left,' etc.) in internal speech, and then reacts in reponse to this associated idea. As practice advances, the associative term drops out of consciousness. Nevertheless, the reaction does not, for a long time, follow directly upon the apprehension of the stimulus; there is, as the reactors put it, a certain resistance to be overcome before the movement can be made. This resistance has not been adequately described; Wundt regards it as a phenomenon of motor inhibition. The movement itself is, as we said above, frequently prepared for by the sensations of intended movement, which some- times last over into the mid-period. They are especially marked if, at the moment of apprehension of the stimulus, there is a tendency to move the wrong finger; they are then characterised as an urgency or impulse to move in a certain way. The stimulus, how- ever, touches off the right movement, without arousing a second kinaesthetic complex in the correlated finger. — A word must now be said with regard to the sensations of in- tended movement. We have called them kinaesthetic sensations; they appear in consciousness as a mode of kinaesthesis; often- times they are referred to organs whose muscles are obviously in contraction. But there is something to be added. Their inten- sity may be out of all proportion to the degree of actual muscular contraction; they may be referred to a muscle-group which, at the time, is sensibly quiescent, and whose later contraction sets up kinaesthesis of a distinguishably different kind. When they occur about the eyes, the observers insist that they are intro- spectively different from the kinaesthetic sensations of attentional adjustment (§ 78). Their place may be taken, in the reaction consciousness, by imaginal processes, by visual images or internal speech. It looks, then, as if they were themselves, at least in part, images rather than sensations, but images of that stable sort which Action may be confused with sensations. We cannot here appeal to cen- trifugal sensory paths (§118) j but we may, following Wundt, make the following tentative hypothesis regarding their central origin.
Consider, first, the ordinary mode of arousal of kinaesthetic sensations. A motor centre sends out excitations to the peripheral motor apparatus with which it is connected; the changes thus set up at the periphery stimulate the kinaesthetic organs; excitations proceed from these to the correlated sensory centres; sensation re- sults. Now suppose that the motor centre stands in direct functional connection with the sensory centres. The excitation, instead of taking the roundabout path to the periphery and back again, may take the straight path from motor to sensory centre; the periph- eral apparatus need not be disturbed. But the sensory centre*, accustomed to respond to excitation by kinaesthetic sensation, will do so under the conditions of this direct excitation; kinaes- thesis, of the stable sensory kind, will appear in consciousness. Ordinarily, the roundabout and the direct paths are both traversed by excitatory processes; in the case of the sensations of intended movement, only the direct path need be involved.
It must be clearly understood that the names given to these compound reactions — discriminative, cognitive, choice — are merely conventional. Discrimination and choice re- fer to the external arrangement of the experiment, and to that alone; in the discriminative reaction we do not dis- criminate, in the choice reaction we may do various things, but we do not choose. Cognition, direct apprehension, is implied in all reactions, simple and compound alike; even in the muscular reaction we cognise 'something different.' The names were given, speculatively, at a time in the his- tory of psychology when experiment was new and analysis still a matter for the future. They have persisted, as names will; it is as difficult to dispossess them as it is to banish the terms 'active' and 'passive' from the doctrine of attention; but the reader must take them simply as labels for certain historical forms of the reaction experi- ment, not as psychological rubrics.
Everything depends, we said above (p. 433), on the attitude which the reactor takes to the experiment; and this attitude itself depends on his understanding of instructions. We must now add that the carrying out of instructions, as understood, depends upon practice; the time of an elaborately planned choice reaction may, if the coordination of stimulus and movement has been sufficiently practised, be the same as that of the simple sensory reaction. It follows from these considerations that the compound reactions are not built up, piece by piece, from the simple; the discriminative and cognitive reactions are not sensory reactions lengthened by the times of discrimination and cognition; the choice reactions are not discriminative reactions lengthened by the time of choice. In other words, we cannot derive the time of discrimination by sub- tracting the sensory from the discriminative reaction time, or the time of choice by subtracting the discriminative from the choice reaction time. This procedure is often followed; the times of discrimination, cognition, choice are often to be found in the text- books; but there is, in fact, no truth in the underlying assumption that the reaction is a chain of separate processes, to which separate