Mr. B. wished to inquire further into a fact found out by several persons by this method: the fact that there is an important difference in the length of a person's reaction time according to the direction of his attention during the experi- ment. If, for example, Mr. X. be tested, it is pos- sible that he may prefer to attend strictly to the signal, letting his finger push the key without direct care and supervision. If this be true, and we then interfere with his way of proceeding, by telling him that he must attend to his finger, and allow the signal to take care of itself, we find that he has great difficulty in doing so, grows embarrassed, and his reaction time becomes very irregular and much longer. Yet another person, say Y, may show just the opposite state of things; he finds it easier to pay attention to his hand, and when he does so he gets shorter and also more regular times than when he attends to the signal-sound.
It occurred to Mr. B. that the striking differ- ences given by different persons in this matter of the most favourable direction of the attention might be connected with the facts brought out by the physiological psychologists in connection with speech; namely, that one person is a " vis- ual," in speaking, using mainly sight images of * The writer.
* The writer.
HOW WE EXPERIMENT ON THE MIND. 129 words, while another is a "motor," using mainly muscular images, and yet another an "auditive," using mainly sound images. If the differences are so marked in the matter of speech, it seemed likely that they might also extend to other func- tions, and the so-called " type " of a person in his speech might show itself in the relative lengths of his reaction times according as he attended to one class of images or another.
Calling this the " type theory " of reaction times, and setting about testing four different persons in the laboratory, the problem was di- vided into two parts; first, to direct all the indi- viduals selected to find out, by examining their mental preferences in speaking, reading, writing, dreaming, etc., the class of images which they or- dinarily depended most upon; and then to see by a series of experiments whether their reac- tion times to these particular classes of im- ages were shorter than to others, and especially whether the times were shorter when attention was given to these images than when it was given to the muscles used in the reactions. The mean- ing of this would be that if the reaction should be shorter to these images than to the correspond- ing muscle images, or to the other classes of images, then the reaction time of an individual would show his mental type and be of use in testing it. This would be a very important matter if it should hold, seeing that many questions both in medicine and in education, which involve the ascertaining of the mental character of the individual person, would profit by such an exact method.
The results on all the subjects confirmed the supposition. For example, one of them, Mr. C., found from an independent examination of him- 130 THE STORY OF THE MIND.
self, most carefully made, that he depended very largely upon his hearing in all the functions mentioned. When he thought of words, he re- membered how they sounded; when he dreamed, his dreams were full of conversation and other sounds. When he wrote, he thought continually of the way the words and sentences would sound if spoken. Without knowing of this, many series of reaction experiments were made on him; the result showed a remarkable difference between the lengths of his reactions, according as he di- rected his attention to the sound or to his hand; a difference showing his time to be one half shorter when he paid attention to the sound. The same was seen when he reacted to lights; the attention went preferably to the light, not to the hand; but the difference was less than in the case of sounds. So it was an unmistakable fact in his case that the results of the reaction experiments agreed with his independent decision as to his mental type.
In none of the cases did this correspondence fail, although all were not so pronounced in their type preferences as was Mr. C.
The second part of the research had in view the question whether reaction times taken upon speech would show the same thing; that is, whether in Mr. C.'s case, for example, it would be found that his reaction made by speaking, as soon as he heard the signal or saw the light, would be shorter when he paid attention to the signal than when he gave attention to his mouth and lips. For this purpose a mouth key was used which made it possible for the subject simply by emitting a puff of breath from the lips, to break an electric current and thus stop the chronoscope HOW WE EXPERIMENT ON THE MIND. 131 as soon as possible after hearing the signal. The mouth key is figured herewith (Fig. 6).
This experiment was also carried out on all the subjects, none of them having any knowledge of the end in view, and the experimenters also not having, as yet, worked out the results of the ear- lier research. In all the cases, again, the results FlG. 6. — Mouth-key (Isometric drawing). The metallic tongue E swings over the mercury H, making or breaking the circuit AHEDB or CEHA. The tongue is moved by a puff of air through the funnel F. (Devised by Prof. W. Libbey.)
showed that, for speech, the same thing held as for the hand — namely, that the shortest reaction times were secured when the subject paid atten- tion to the class of images for which he had a general preference. In Mr. C.'s case, for example, it was found that the time it took him to speak was much shorter when he paid strict attention tc?
132 THE STORY OF THE MIND.
the expected sound than when he attended to his vocal organs. So for the other cases. If the individual's general preference is for muscular images, we find that the quickest time is made when attention is given to the mouth and lips. Such is the case with Mr. B.
The general results go to show, therefore — and four cases showing no exception, added to the indications found by other writers, make a gen- eral conclusion very probable — that in the differ- ences in reaction times, as secured by giving the attention this way or that, we have general indi- cations of the individual's temperament, or at least of his mental preferences as set by his education. These indications agree with those found in the cases of aphasia known as "motor," "visual," "auditory," etc., already mentioned. The early examination of children by this method would probably be of great service in determining prop- er courses of treatment, subjects of study, modes of discipline, tendencies to fatigue and embar- rassment, and the direction of best progress in education.
This research may be taken to illustrate the use of the reaction-time method in investiga- ting such complex processes as attention, tem- perament, etc. The department which includes the various time measurements in psychology is now called Mental Chronometry, the older term, Psychometry, being less used on account of its ambiguity.
III. An Optical Illusion. — In the sphere of vi- sion many very interesting facts are constantly coming to light. Sight is the most complex of the senses, the most easily deranged, and, withal, the most necessary to our normal existence. The HOW WE EXPERIMENT ON THE MIND. 133 report of the following experimental study will have the greater utility, since, apart from any in- trinsic novelty or importance the results may prove to have, it shows some of the general bear- ings of the facts of vision in relation to ^Esthetics, to the theory of Illusions, and to the function of Judgment.
Illusion of the senses is due either to purely physiological causes or to the operation of the principle of Assimilation, which has already been remarked upon. In the latter case it illustrates the fact that at any time there is a general dis- position of the mind to look upon a thing under certain forms, patterns, etc., to which it has grown accustomed; and to do this it is led sometimes to distort what it sees or hears unconsciously to itself. So it falls into errors of judgment through the trap which is set by its own manner of work- ing. Nowhere is the matter better illustrated than in the sphere of vision. The number of illusions of vision is remarkable. We are constantly tak- ing shapes and forms for something slightly differ- ent from what, by measurement, we actually find them to be. And psychologists are attempting — with rather poor success so far — to find some general principles of the mechanism of vision which will account for the great variety of its illu- sions.
Among these principles one is known as Con- trast. It is hardly a principle as yet. It is rather a word used to cover all illusions which spring up when surfaces of different sizes and shapes, looked at together or successively, are misjudged with reference to one another. Wishing to investigate this in a simple way, the following experiment was planned and carried out by Mr. B.
134 THE STORY OF THE MIND.
He wished to find out whether, if two detached surfaces of different sizes be gazed at together, the linear distances of the field of vision (the whole scene visible at once) would be at all misjudged. To test this, he put in the window (W) * of the dark room a filling of white cardboard in which two square holes had been cut (S S'). The sides of the squares were of certain very unequal lengths. Then a slit was made between the middle points of the sides of the squares next to each other, so that there was a narrow path or trough joining the squares between their adjacent sides. Inside the dark room he arranged a bright light so that it would illuminate this trough, but not be seen by a person seated some distance in front of the win- dow in the next room. A needle (D) was hung on a pivot behind the cardboard, so that its point could move along the bright trough in either di- rection; and on the needle was put the armature (A) of an electro-magnet which, when a current passed, would be drawn instantly to the magnet (E), and so stop the needle exactly at the point which it had then reached. A clock motor (Cm) was arranged in such a way as to carry the needle back and forth regularly over the slit; and the electro-magnet was connected by wires with a punch key (K) on a table beside the subject in the next room. All being now ready, the subject, Mr. S., is told to watch the needle which appears as a bead of light travelling along the slit, and stop it when it comes to the middle point of the line, by pressing the electric key. The experi- menter, who stands behind the window in the dark room, reads on a scale (mm.) marked in millime- * This and the following letters in parentheses refer to Fig. 7 HOW WE EXPERIMENT ON THE MIND. 135 tres the exact point at which the needle stops, re- leases the needle by breaking the current, thus allowing it to return slowly over the line again. This gives the subject another opportunity to 136 THE STORY OF THE MIND.
stop it at what he judges to be the exact middle of the line, and so on. The accompanying figure (Fig. 7) shows the entire arrangement.
A great many experiments performed in this way, with the squares set both vertically and horizontally, and with several persons, brought a striking and very uniform result. The point selected by the subject as the middle is regu- larly too far toward the smaller square. Not a little, indeed, but a very appreciable amount. The amount of the displacement, or, roughly speaking, of the illusion, increases as the larger square is made larger and the smaller one smaller; or, put in a sentence, the amount varies directly with the ratio of the smaller to the larger square side.
Finding such an unmistakable illusion by this method, Mr. B. thought that if it could be tested by an appeal to people generally, it would be of great gain. It occurred to him that the way to do this would be to reverse the conditions of the experiment in the following way: He prepared the figures given in Plate I, in which the two squares are made of suitable relative size, a line is drawn between them, and a point on the line is plainly marked. This he had printed in a weekly journal, and asked the readers of the journal to get their friends, after merely looking at the figure (i. e., without knowing the result to be expected), to say — as the reader may now do before reading further — whether the point on the line (Plate I) is in the middle or not; and if not, in which direction from the true middle it lies. The results from hundreds of persons of all man- ner of occupations, ages, and of both sexes, agree in saying that the point lies too far toward the o HOW WE EXPERIMENT ON THE MIND. 137 larger square. In reality it is in the exact middle. This is just the. opposite of the result of the ex- periments in the laboratory, where the conditions were the reverse, i. e., to find the middle as it ap- pears to the eye. Here, therefore, we have a com- plete confirmation of the illusion; and it is now fully established that in all cases in which the conditions of this experiment are realized we make a constant mistake in estimating distances by the eye.* For instance, if a town committee wish to erect a statue to their local hero in the public square, and if on two opposite sides of the square there are buildings of very different heights, the statue should not be put in the exact middle of the square, if it is to give the best effect from a dis- tance. It should be placed a little toward the smaller building. A colleague of the writer found, when this was first made public, that the pictures in his house had actually been hung in such a way as to allow for this illusion. Whenever a picture was to be put up between two others of considera- ble difference of size, or between a door (large) and a window (small), it had actually been hung a lit- tle nearer to the smaller — toward the small pic- ture or toward the window — and not in the true middle.
It is probable that interesting applications of this illusion may be discovered in aesthetics. For wherever in drawing or painting it is wished to indicate to the observer that a point is midway * In redrawing the figure on a larger sheet (which is rec- ommended), the connecting line may be omitted, only the mid-point being marked. Some get a better effect with two circles, the intervening distance being divided midway by a dot, as in Plate IL 138 THE STORY OF THE MIND.
between two lines of different lengths, we should find that the artist, in order to produce this effect most adequately, deviates a little from the true middle. So in architecture, the effect of a con- trast of masses often depends upon the sense of bilateral balance, symmetry, or equality, in which this visual error would naturally come into play. Indeed, it is only necessary to recall to mind that one of the principal laws of aesthetic effect in the matter of right line proportion is the rela- tion of "one to one," as it is called, or equal divi- sion, to see the wide sphere of application of this illusion. In all such cases the mistake of. judg- ment would have to be allowed for if masses of unequal size lie at the ends of the line which is to be divided.
IV. The Accuracy of Memory. — Another in- vestigation may be cited to illustrate quite a dif- ferent department. It aimed to find out some- thing about the rate at which memory fades with the lapse of time. Messrs. W., S., and B.* began by formulating the different ways in which tests may be made on individuals to see how accurate their memories are after different periods of time. They found that three different tests might be employed, and called them "methods" of investi- gating memory. These are, first, the method of Reproduction. The individual is asked to re- produce, as in an oral or written examination, what he remembers of something told him a certain time before. This is the ordinary method of the schools and colleges, of civil-service examina- tions, etc. Second, the method of Identifica- tion, which calls upon the person to identify a * Prof. H. C. Warren, Mr. W. J. Shaw, and the writer.
HOW WE EXPERIMENT ON THE MIND. 139 thing, sentence, report, etc., a second or third time, as being the same in all respects as that which he experienced the first time it appeared. Third, the method of Selection, in which we show to the person a number of things, sentences, reports, descriptions of objects, etc., and require him to select from them the ones which are exactly the same as those he has had before. These methods will be better understood from the account now to be given of the way they were carried out on a large number of students.
The first experiments were made by Messrs. S. and B. in the University of Toronto on a class of students numbering nearly three hundred, of whom about one third were women. The in- structors showed to the class certain squares of cardboard of suitable size, and asked them to do the following three things on different days: First, to reproduce from memory, with pencil on paper, squares of the same size as those shown, after intervals of one, ten, twenty, and forty minutes (this gives results by the method of Reproduction); second, to say whether a new set of squares, which were shown to them after the same intervals, were the same in size as those which they had originally seen, smaller, or larger (illustrating the method of Identification); third, they were shown a number of squares of slightly different sizes, again at the same inter- vals, and asked to select from them the ones which they found to be the same size as those ori- ginally seen (method of Selection).
The results from all these experiments were combined with those of another series, secured from a large class of Princeton students; and the figure (Fig. 8) shows by curves something of the THE STORY OF THE MIND.
result. The figure is given in order that the read- er may understand by its explanation the " graphic method " of plotting statistical results, which, with various complications, is now employed in psy- chology as well as in the other positive sciences.
FIG. 8. — Memory curves: I. Method of Selection. Identification.
"fr II. Method of Briefly described in words, it was found that the three methods agreed (the curves are paral- lel)* in showing that during the first ten minutes there was a great falling off in the accuracy of memory (slant in the curves from o to 10); that then, between ten and twenty minutes, memory re- mained relatively faithful (the curves are nearly level from 10 to 20), and that a rapid falling off in accuracy occurred after twenty minutes (shown by the slant in the lines from 20 to 40).
Further, the different positions qf the curves show certain things when properly understood. The curve secured by the method of Reproduction (not given in the figure) shows results which are least accurate, because most variable. The rea- son of this is that in drawing the squares to re- produce the one remembered, the student is in- * This figure shows curves for two of the methods only, Selection and Identification.
HOW WE EXPERIMENT ON THE MIND. 141 fluenced by the size of the paper he uses, by the varying accuracy of his control over his hand and arm (the results vary, for example, according as he uses his right or left hand), and by all sorts of associations with square objects which may at the time be in his mind. In short, this method gives his memory of the square a chance to be fully assimilated to his current mental state during the interval, and there is no corrective outside of him to keep him true.
That this difficulty is a real one no one who has examined students will be disposed to deny. When we ask them to reproduce what the text- book or the professor's lectures have taught, we also ask them to express themselves accurately. Now the science of correct expression is a thing in which the average student has had no training. With his difficulty in remembering is connected his difficulty of expression; and with it all goes a certain embarrassment, due to responsibilty, per- sonal fear, and dread of disgrace. So the results finally obtained by this method are really very complex.
One of the curves, that given by the method of Selection (I), also shows memory to be inter- fered with by a certain influence. We saw in con- nection with the experiments reported above that, even in the most elementary arrangements of squares in the visual fields, an element of contrast comes in to interfere with our judgment of size. This we find confirmed in these experiments when the method of Selection is used. By this method we show a number of squares side by side, asking the individual to select the one he saw before. All the squares, being shown at once, come into contrast with one another on the background; and 142 THE STORY OF THE MIND.
so his judgment of the size of the one he remembers is distorted. This, again, is a real influence in our mental lives, leading to actual illusion. An un- scrupulous lawyer may gradually modify the story which his client or a witness tells by constantly adding to what is really remembered, other details so expertly contrasted with the facts, or so neatly interposed among them, that the witness gradually incorporates them in his memory and so testifies more nearly as the lawyer desires. In our daily lives another element of contrast is also very strong — that due to social opinion. We constantly modify our memories to agree more closely with the truths of social belief, parin'g down uncon- sciously the difference between our own and oth- ers' reports of things. If several witnesses of an event be allowed to compare notes from time to time, they will gradually come to tell more nearly the same story.
. The other curve (II) in the figure, that secured by the method of Identification, seemed to the investigators to be the most accurate. It is not subject to the errors due to expression and to contrast, and it has the advantage of allowing the subject the right to recognise the square. It is shown to him again, with no information that it is the same, and he decides whether from his remem- brance of the earlier one, it is the same or not. The only objection to this method is that it re- quires a great many experiments in order to get an average result. To be reliable, an average must be secured, seeing that, for one or two or a few trials, the student may guess right without remembering the original square at all. By taking a large number of persons, such as the three hun- dred students, this objection may be overcome.
HOW WE EXPERIMENT ON THE MIND. 143 Comparing the averages, for example, of the re- sults given by the men and women respectively, we found practically no difference between them. This last point may serve to introduce a dis- tinction which is important in all work in ex- perimental psychology, and one which is recog- nised also in many other sciences — the distinction between results obtained respectively from one individual and from many. Very often the only way to learn truth about a single individual is to investigate a number together. In all large classes of things, especially living things, there are great individual differences, and in any particular case this personal variation may be so large that it ob- scures the real nature of the normal. For exam- ple, three large sons may be born to two small parents; and from this case alone it might be in- ferred that all small parents have large sons. Or three girls might have better memories than three boys in the same family or school, and from this it might be argued that girls are better endowed in this direction than boys. In all such cases the proper thing to do is to get a large number of cases and combine them; then the preponderance which the first cases examined may have shown, in one direction or the other, is corrected. This gives rise to what is called the statistical method; it is used in many practical matters, such as life insurance, but its application to the facts of life, mrnd, variation, evolution, etc., is only begun. Its neglect in psychology is one of the crying defects of much recent work. Its use in complicated problems involves a mathematical training which people generally do not possess; and its misuse through lack of exactness of observation or igno- rance of the requirements is worse than its neglect.
144 THE STORY OF THE MIND.
Another result came out in connection with these experiments on memory, which, apart from its practical interest, may serve to show an addi- tional resource of experimental psychology. In making up the results of a series of experiments it is very important to observe the way in which the different cases differ from one another. Some cases may be so nearly alike that the most extreme of them are not far from the average of them all; as we find, for example, if we measure a thousand No. 10 shot. But now suppose we mix in with the No. 10 some No. 6 and some No. 14, and then take the average size; we may now get just the same average, and we can tell that this pile is different from the other only by observing the individual measurements of the single shot and setting down the relative frequency of each particular size. Or, again, we may get a different average size in one of two ways: either by taking another lot of uni- form No. 14 shot, let us say, or by mixing with the No. 10 a few very large bullets. Which is actually the case would be shown only by the examination of the individual cases. This is usually done by comparing each case with the average of the whole lot, and taking the average of the differences thus secured — a quantity called the "mean variation."
In the case of the experiments with the squares, the errors in the judgments of the students were found to lie always in one direction. The answers all tended to show that they took, for the one originally shown, a square which was really too large. Casting about for the reason of this, it was considered necessary to explain it by the supposi- tion that the square remembered had in the inter- val become enlarged in memory. The image was larger when called up after ten or twenty min- HOW WE EXPERIMENT ON THE MIND. 145 utes than it was before. This might be due to a purely mental process; or possibly to a sort of spreading out of the brain process in the visual centre, giving the result that whenever, by the re- vival of the brain process, the mental image is brought back again to mind, this spreading out shows itself by an enlargement of the memory image. However it may be explained, the indica- tions of it were unmistakable — unless, of course, some other reason can be given for the uniform direction of the errors; and it is further seen in other experiments carried out by Messrs. W. and B. and by Dr. K.* at a later date.