Part 7 (1/2)
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 as soon as possible after hearing the signal.
The mouth key is figured herewith (Fig. 6).
[Ill.u.s.tration: FIG. 6.--Mouth-key (Isometric drawing) The metallic tongue E swings over the mercury H, making or breaking the circuit A H E D B or C E H A. The tongue is moved by a puff of air through the funnel F. (Devised by Prof. W. Libbey.)]
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 earlier research. In all the cases, again, the results showed that, for speech, the same thing held as for the hand--namely, that the shortest reaction times were secured when the subject paid attention to the cla.s.s 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 to 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 general conclusion very probable--that in the differences in reaction times, as secured by giving the attention this way or that, we have general indications 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 proper courses of treatment, subjects of study, modes of discipline, tendencies to fatigue and embarra.s.sment, and the direction of best progress in education.
This research may be taken to ill.u.s.trate the use of the reaction-time method in investigating such complex processes as attention, temperament, 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 vision 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 report of the following experimental study will have the greater utility, since, apart from any intrinsic novelty or importance the results may prove to have, it shows some of the general bearings of the facts of vision in relation to aesthetics, 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 a.s.similation, which has already been remarked upon. In the latter case it ill.u.s.trates the fact that at any time there is a general disposition 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 working. Nowhere is the matter better ill.u.s.trated than in the sphere of vision. The number of illusions of vision is remarkable. We are constantly taking shapes and forms for something slightly different 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 illusions.
Among these principles one is known as Contrast. 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.
Wis.h.i.+ng to investigate this in a simple way, the following experiment was planned and carried out by Mr. B.
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)[5] 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 window 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 direction; and on the needle was put the armature (A) of an electro-magnet which, when a current pa.s.sed, 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 experimenter, who stands behind the window in the dark room, reads on a scale (mm.) marked in millimetres the exact point at which the needle stops, releases the needle by breaking the current, thus allowing it to return slowly over the line again. This gives the subject another opportunity to 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.
[Footnote 5: This and the following letters in parentheses refer to Fig. 7]
[Ill.u.s.tration: FIG. 7]
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 regularly 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 manner of occupations, ages, and of both s.e.xes, agree in saying that the point lies too far toward the larger square. In reality it is in the exact middle. This is just the opposite of the result of the experiments in the laboratory, where the conditions were the reverse, i. e., to find the middle as it appears to the eye. Here, therefore, we have a complete 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.[6]
[Footnote 6: In redrawing the figure on a larger sheet (which is recommended), 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 II.]
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 distance. 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 considerable difference of size, or between a door (large) and a window (small), it had actually been hung a little nearer to the smaller--toward the small picture 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 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 contrast of ma.s.ses 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 princ.i.p.al laws of aesthetic effect in the matter of right line proportion is the relation of ”one to one,” as it is called, or equal division, to see the wide sphere of application of this illusion. In all such cases the mistake of judgment would have to be allowed for if ma.s.ses of unequal size lie at the ends of the line which is to be divided.
IV. _The Accuracy of Memory._--Another investigation may be cited to ill.u.s.trate quite a different department. It aimed to find out something about the rate at which memory fades with the lapse of time.
Messrs. W., S., and B.[7] 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 investigating memory. These are, first, the method of Reproduction.
The individual is asked to reproduce, 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 examinations, etc. Second, the method of Identification, which calls upon the person to identify a 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.
[Footnote 7: Prof. H. C. Warren, Mr. W. J. Shaw, and the writer.]
The first experiments were made by Messrs. S. and B. in the University of Toronto on a cla.s.s of students numbering nearly three hundred, of whom about one third were women. The instructors showed to the cla.s.s 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 (ill.u.s.trating the method of Identification); third, they were shown a number of squares of slightly different sizes, again at the same intervals, and asked to select from them the ones which they found to be the same size as those originally seen (method of Selection).
The results from all these experiments were combined with those of another series, secured from a large cla.s.s of Princeton students; and the figure (Fig. 8) shows by curves something of the result. The figure is given in order that the reader may understand by its explanation the ”graphic method” of plotting statistical results, which, with various complications, is now employed in psychology as well as in the other positive sciences.
[Ill.u.s.tration: FIG. 8.--Memory curves: I. Method of Selection. II.
Method of Identification.]
Briefly described in words, it was found that the three methods agreed (the curves are parallel)[8] in showing that during the first ten minutes there was a great falling off in the accuracy of memory (slant in the curves from 0 to 10); that then, between ten and twenty minutes, memory remained 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).