CHAPTER XVI

KEACTION-TIME

For the Whole Claaa,* "QuiCK as thought" is often taken to mean infinitely short time, or no time at ail. Yet thinking is a distressingly slow process with some of us. A century and a half ago a distinguished physiologist estimated that the speed of the nerve-impulse was about 57,600,000,000 feet per second; a century later it was measured and found to be, in round numbers, 100 feet per second. It was for some time thought to hâve a speed comparable with the speed of the electric current, but the electric current would flash half the distance around the globe at the equator while a nerve-impulse passes from f oot to head in man. The conceptions of the time of mental

* If the class is large, it may be divided into sections of about twelve to fifteen. Select a conductor, a timer, and a recorder for each section a week in advance, and let them train themselves so that they are prepared to conduct the experiment efficiently and economically. The conductor shall hâve gênerai command; the timer shall take the time with a stop-watch; the recorder shall take full notes. The conductor and the recorder cannot be in the chain. If no stop-watch is available, the timer must also be out of the chain so that he can time by counting the ticks of a watch, usually fifths of a second. He can then count by groups of ten-fifths, but may adapt the method of counting to the length of the chain.

The experiment may be performed in one hour if proper préparations hâve been made and the reading of the explanatory parts is postponç^ until the experiments hâve been completed.

processes hâve undergone equally great revision within the same period. We now measure the duration of mental processes, and thèse measurements give the mental processes concreteness and a natural setting. They not only f urnish the time of the mental act, but also serve to isolate the selected process and make it tangible for the purpose of psychological analysis and synthesis.

The term reaction-time is used to dénote thèse measurements because it is customary to arrange the experiment so that the termination of the act is marked by a reaction.*

To enable the whole class to participate, and to avoid the use of elaborate apparatus, we shall adopt the chainreaction method. The class forms a chain and a given signal is passed as rapidly as possible from one to the next until it has completed the round. The total time for the chain is divided by the number of participants, which apportions the average individual time required

• "A great variety of actions may be viewed as responses to stimuli. There is a flash of light, and we wink; a burning cinder faUs upon the hand, and we draw it away; a beU rings, and the engineer starts his train, or the servant opens the door, or we go down to dinner; the clock strikes, and we stop work, or go to keep an appointment. Again, in such an occupation as copying, every letter or word seen acts as a stimulus, to which the written letter or word is the response; in piano-playing, and the guidance of complicated machinery, we see more elaborate instances of similar processes. The printer distributing "pi", the postoflBce clerk sorting the mails, are illustrations of quick forms of reaction, in which the différent letters of the alphabet or the différent addresses of the mail matter act as the stimuli, and the placing them in their appropriate places follows as the response. In many games, such as tennis or cricket, the various ways in which the balls are seen to come to the striker are the stimuli, for each variation of which there is a précise and complex form of response in the mode of retuming the bail." (Jag^ trow, "The Time- relations of Mental Phenomena.")

for the act. It is essential that ail should understand clearly what the act is and what attitude to take. Exp. 1 will represent simple réactions; ail the foUowing experiments represent complex reactions. It is in the latter that we measure the time of mental processes according to the plan hère adopted.

1. Simple Réaction, a. Visual. — The signal shall be the quick downward movement of a pencil, and this signal shall be passed as rapidly as possible from one to another. Let the class form a circle and face away from the center. At the conductor's command "Eeady!", each one shall raise a pencil into plain view of the person to his right ; and, about three seconds af ter the conductor's warning "Now!", the timer shall simultaneously start the stop-watch and give the signal to the person at his right, who shall in turn give it to the one at his right, and so on, the signal being passed as rapidly as possible until it reaches the timer again; and he, instead of passing it on, shall stop the stopwatch.

In this and each of the following experiments make five successive trials; compute the average of the five trials and divide by the number of participants.

h, Auditory, — The signal shall be the exclamation "Up!". Let ail keep their eyes closed. In other respects proceed as in Exp. 1 a.

c. Tactual, — The signal shall be a tap on the right shoulder. Let each one turn 90° tô the right and, at the conductor's command "Ready !", place the tip of the index-finger of the right hand so that it ail but touches

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the right shoulder of the person in front of him, Lex ail keep their eyes closed. In other respects proceed as in Exp. 1 a.

The method of measurement hère used is crude. The time-measurement is not fine *or exact enough; the signal-response is too indefinite ; each participant labors under différent conditions; there is little opportunity for introspection; the practice is inadéquate and there are many other shortcomings. Yet the experiment serves very well to bring ont the expérience of timerelations.

In the laboratory the exact experiments are made with chronoscopes or chronographs which measure small intervais of time accurately. A single observer is isolated in an observation-room from which ail disturbing stimuli may be excluded. The signal and the response are simplified and made more exact. The observer is trained, numerous trials are made, the variability of the records is computed, the reaction is fractionated * for the purpose of the introspection, and the conditions may be controUed and regulated in great détail.

Thèse "simple reactions" may be reduced to their component parts and, under certain conditions, the time of each of thèse components may be measured. The complexity of the process becomes apparent when we attempt to trace the physical and the mental steps in the act as in the foUowing outline.

* That is, the observer introspects one aspect of the reaction in one set of experiments and then repeats the experiment and introspects another aspect, etc.

THE PHYSICAL PBOCESS THE MENTAL PBOCESS

1. The response of the sensé- 1. The idea of the signal in organ * and the transmissioYi expectant attention.

of the nerve-impulse to the cortex of the brain.

2. The progress of this im- 2. The perception of the sigpulse through the cortex. nal, the association of the signal with the response, and the fiât of the will to respond.

3. The transmission of the 3. The idea of the movement nerve-impulse to the muscles, foUowed by sensation of the the response of the muscles, movement.

and the transmission of sensory impulse from the muscles to the cortex.

The very incompletenesa and arbitrariness of this outline serves to bring out the complexity of the act. Thèse three steps are ail complex, both on the physical and the mental sides. The real reaction consists in the second step, in which there is a direct corrélation between the mental and the neural process. So far as the mental act is concerned, the first step is merely a préparation and the third step is merely a conséquence of the reaction. Of the total act, the reaction proper (the second step) occupies but a small portion of the time. There are neural processes in the cortex which correspond to ail three steps on the mental side.

Hère, then, we hâve not measured the time of the mental act of reaction, but the time of a unique set of physical and mental processes in which the conscious

♦The transmission of the sound- waves through the ear and their conversion into a nerve-impulse; the overcoming of the inertia of the retina; or the overcoming of the inertia of the tactual sense-organ.

210 KEACTION-TIME

reaction is the essential élément. The simple réaction becomes simpler and shorter, as well as more uniform and irrésistible, with practice ; and it tends to be less and less emphatic in consciousness until it becomes practitally automatic. AU this is implied in and characteristic of the acquisition of skill in any sort of activity. Skill means a quick, uniform, appropriate, and but f aintly conscious act.

Life is a séries of reactions. Therefore, in selecting some of thèse for expérimentation, we may hâve great variety in conditions. Among the principal variables in simple reactions are the f oUowing : the nature of the impression or signal, the strength of the stimulus, the mode of reaction, the direction of attention, expectation, distraction, degree of concentration, practice, fatigue, individual différences, mental and physical state of health, the influence of stimulants, the influence of mental encouragement or discouragement, etc.

Take one of thèse, the direction of attention. We find three characteristic types of simple reaction with référence to this: the sensory, in which attention is directed to the stimulus ; the motor, in which attention is directed to the response ; and the central, in which attention is not focused upon either stimulus or response exclusively, but is allowed to oscillate or take a sort of middle ground. The motor is the quickest and most effective form, and there is a tendency to pass f rom the other types to this with practice. ' It may become so simple as to be purely a cérébral reflex.

Or take practice. Practice shortens the reaction-time so rapidly that it becomes a disturbing factor in the

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présent expérimenta. The gain by practice in Exp. 1 c may so reduce the time in Exp. 2 that the additional faetor there involved may not show appreciably in the time. It is customary to distribute the practice evenly among trials which are to be compared. If time had permitted it, that should hâve been done in the présent experiments.

2. Discrimination. — The signal shall be a tap, as in Exp. 1 Cy but it may be given on either shoulder, and the person touched shall respond as soon as he knows which shoulder was touched, but he must détermine beforehand which side he shall touch ; i.e., the signal shall not détermine what the response shall be, but the response shall not be given until the signal has been distinguished as a right-side or a left-side signal. Let each one hold the tip of a finger close to each shoulder of the person in front of him. In other respects proceed as in Exp. 1 c.

This act involves the simple reaction to touch plus discrimination ; to get the discrimination-time, subtract the time in Exp. 1 c f rom the time in this experiment.

3. Choice. — The signal shall be a tap on either shoulder, as in Exp. 2, but the response must be made on the same side as the signal is received, i.e., the person touched must sélect one of two possible responses according to directions after he has received the signal. In other respects proceed as in Exp. 2.

This act involves the reaction after discrimination, as in Exp. 2, plus the sélective choice ; to get the time of the choice, subtract the time in Exp. 2 from this.

Discrimination and choice are common acts in life.

212 KEACTION-TIME

The experiments might hâve been varied as to the number of distinctions or choioes, the degree of similarity of the impressions, the spécifie nature of the impressions, foreknowledge of the conditions, adaptation to the individual, etc.

Discrimination and choice are clearly mental processes. Exps. 2 and 3 illustrate how we may isolate one process after another for the measurement of its duration, for* introspection, and for the building up of a complex mental act of which the éléments are known and under control.

4. Cognîtion. — The signal shall be a word, and the response shall be another word, predetermined, but spoken only as soon as the signal-word has been "cognized''. Each response becomes the signal for the next person. In other respects proceed as in Exp. 1 a.

This act involves reaction after cognition ; to get the cognition-time, subtract the simple reaction to sound (1 fc) from this.

5. Free Association. — The signal shall be a word, and the response shall be another word — the first word which comes to mind upon hearing the signal. Be sure to call out the first word which can possibly be drawn from the imagery suggested by the signal-word ; do not stop to reason or discriminate.* The response becomes the signal for the next, and so on. In other respects proceed as in Exp. 4.

* As in the experiments on the laws of association, it is ailimportant that the response shall be immédiate and unreflective.

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This act involves simple reaction, eognition, and free association ; to get the time of the free association, subtract the time in Exp. 4 from this.

6. Restricted Association: Memory. — The signal shall bè a word, and the response shall be another word which begins with the final letter of the signal. The response becomes the signal for the next, and so on. In other respects proceed as in Exp. 4.

This act involves simple reaction, eognition, and a partially restricted association; to get the time of this association, subtract the time in Exp. 4 from this.

7. Judgment,— The signal shall be the naming of two edibles, and the response shall be the naming of the one of thèse two which is preferred and one other edible thought of beforehand. The response becomes the signal for the next, and so on. In other respects proceed as in Exp. 4.

To get the time of judgment proper, measure the time of simple reaction after eognition when the signal and the response each consist of two words, as above, and subtract that time from the above gross time.

What hâve we measured in thèse complex reactions ? We hâve measured the time of certain purely mental acts of discrimination, choice, eognition, association, memory, and judgment.

But hère a wàming and qualification is necessary. Complex mental acts are not made up of simple acts, each butting end to end against one another in time. The total process is ordinarily a fusion in which, how-

ever, we may trace essential éléments or movements. Thus, although the mode of signaling and the mode of response were identical in Exps. 1 and 2, it is not legitimate to assume that the act of discrimination was sandwiched in between thèse without modifying them, or that the discrimination f oUowed step 2 in the simple reaction without modifying that step. The act of discrimination gradually fused, on the one hand, with the act of perception of the signal and, on the other hand, with the response. The perception-discriminationresponse became one act.

The prooess of élimination which we hâve foUowed therefore does some violence to fact, and many authorities prefer not to use it. For the purpose of most psychological measurements the time of the total complex act is quite as serviceable as the time of an isolated portion of the act. But to measure the time of a mental process strictly, it is necessary to use the method of élimination. And it is justified provided we make no superficial assumptions as to rigid démarcations between mental components of an act and adapt the method to the purpose in hand. Even allowing for a reasonable amount of fusion or overlapping, the time-measurement cannot be far from right. In stating a measurement, the fusion is taken for granted. But it is literally indisputable, e.g., that a given act of discrimination united with a simple reaction lengthens the time by .06 sec.

Someone may contend that thèse are ail purely physiological processes that we hâve measured. Paradoxical though it may seem, we may admit the correctness of the contention. Modem psycbçlogy rests upon

the hypothesis that there is a neural process parallel to every mental process. There is great diversity of opinion as to the nature of the connection, but as to the f act of corrélation ail are agreed. If we are capable of thinking of thèse processes in terms of neural action, it is certainly correct and legitimate to do so. Instead of speaking of the mental acts of choice, memory, and judgment, we are at liberty to speak of thèse acts in terms of their neural concomitants. But what do we know about those ? Express the fact of judgment in terms of neural action if you can ! Try to get any sort of crude conception of it and you f ail. The thing we hâve experienced, the thing we know most concretely, is the mental act. The fact of a neural concomitant is a good hypothesis, but we hâve no direct knowledge of the nature of that neural process. We know infinitely more of the mental than of the physical: and the mental is the object of interest and use, the physical being merely a condition ; hence we prefer to speak in terms of the mental.

Ail the mental processes hère studied are correlated with the neural process mentîoned in step 2 of the outline of simple reaction ; there is only a différence in complexity. But cérébral physiology and physiological psychology hâve very little to tell us in the way of differentiation or description of thèse central processes.

There are three factors in the customary numerical records of reaction-measurements which are often of equal if not greater significance than the average time of the act. Thèse are the mean variation, the number and kind of errors, and the "mode." The mean variation îs a measure of the reliability of the measurement

and the unîf ormity of the act, and the errors are a measure of the quality of the work done. The mode is that record around whieh the other records tend to bunch ; it may or may not be the average. If a séries of records has more than one mode, that indicates that there is some disturbing factor in the measurement. The four factors taken together may measure changes in capacity for quickness, uniformity, and reliability of action.

Knowledge of the time of a mental process is in îtself of little value. The value of mental chronometry lies in its being a means of comparison. But the timemeasurement becomes a sort of scale or foot-rule which may be employed in a great variety of ways. It has probably been used more than any other mode of measurement of its class in psychology. Indeed, in the early period of expérimental psychology, persons would ask if expérimental psychology had anything but reaction-experiments to offer.

It may be employed to measure certain changes in capacity, such as the effect upon mental capacity of drugs, différent types of exercise, rest, practice, fatigue, effort, mental encouragement, health, ideational type, etc. One method of studying fatigue may serve to illustrate this class of applications. The experiment may be so arranged that an individual engages in a chain of reactions. Each response brings out the signal for the next. He must work at maximum speed and without interruption for a long period, say one, two, or three hours. The reaction is the work which fatigues, and the continuons graphie record of the whole séries of re-

action-times contains the measure of capacity for this particular work under various stages of fatigue. The average time in a given minute is the measure of the alertness, the mean variation of the reaction-times during the same period is a measure of the power of application, and the record of the number and kind of errors is a measure of the quality of the work done.

It may be used in the comparison of groups of individuals for statistical, anthropological, educational, commercial, and other purposes. It then shows the minimum time, the variability, and the quality of any act on which we may make the comparison. Do women ordinarily form quicker judgments than men in a given situation ? In either case, which is the more likely to be right? How does readiness in form-discrimination vary with âge, sex, intelligence, race, type of high-school training, etc. ? What élément in form is it that gives one sprinter the advantage over another in the start? Which of several candidates has the best natural ability for bank-teller? Such are some of the questions that may be solved by appropriate reaction-measurements.

It may be used as a measure of discernible différences in any of the sensés ; e.g., to détermine which one of two or more grays differs most from a given standard gray. It has been of good service in determining the relative legibility of différent kinds of printing-type. It may be used as a means of determining individual peculiarities in imagery, in working out laws of association and memory, in studying manifestations of the subconscious, etc. The controUed conditions which it demands are most favorable to a close and intimate view of the inter-

relations of éléments in a complex act. And it is not without value as a rigid discipline in praetical exercises for the development of keenness in perception, memory, reasoning, and action.

Historically, interest in the reaction-measurement haa passed through several phases. It began over a hundred years ago in the study of the personal équation of astronomers. Then the physiologists became interested in the measurement of the speed of the nerve-impulse by this method. This roused the psychologists to the measurement of the time of mental processes. At the présent time the interest of the psychologists centers upon its use as an aid in the analysis and synthesis of action.

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