Elementary experiments in psychology

Preface

Tuis manual is designed to meet the requirements for a series of individual experiments in the first course in psychology. It makes individual experiments, as opposed to class demonstrations, practicable, regardless of laboratory facilities or the size of the class. The student 1s given means and encouragement for pursuing each problem intensively in order that he may acquire independence of thought and action, realize the actuality of mental processes, and get here and there a vision of the vastness, the orderliness, the practical signifieance, and the charms of mental life.

No laboratory facilities are required. In this there is a triple gain: it saves the manifolding of equipment, it frees the student from the technicalities incidental to the manipulation of apparatus at a time when his energies need to be conserved for the grasping of the psychological problem, and it saves time for the class period, the experiments being adapted for outside assignments. The apparatus other than that ordinarily at the disposal of students is supplied with the book in the accompanying envelope.*

* The president of a college asked a distinguished psychologist how much money his board ought to appropriate for the equipment of a fair elementary laboratory. The reply came: “Three thousand dollars a year for a good instructor and one dollar for paper and pins.” This manual supplies the paper and pins and, in part, the instructor.

lil iv PREFACE

The experiments are independent and self-explanatory. Provided the manual is used in connection with the customary elementary text-book or lectures, the experiments require no introduction; the directions are adequate, and the*running comment furnishes the setting for each step and enables the student to see the significance of the results. The beginner needs much help in his experiments in psychology, and there is no more practical way of giving it than through a manual.

This is not a laboratory manual. It is a manual of experiments which the student should perform before he is admitted to the laboratory, or in case he does not intend to pursue the subject beyond one course. It is not a text-book by itself, but a supplement to any good text-book. It does not review the field of psychology, but simply furnishes the intensive, individual, experimental part of the instruction. It does not furnish technical instruction on methods of experimenting, but, like the conversational method of teaching language, everywhere encourages right procedure. It does not purport to cover the most important matters; sometimes an almost insignificant topic (for example, the subject of the first chapter) is chosen for the purpose of deepening insight. It by no means supplants the class demonstrations and experiments, except in the few topics selected, and even here the instructor may profitably supplement and show how the same experiments may be performed by the usual laboratory apparatus.

The manual presupposes such knowledge of the nervous system as is imparted by the text-books most used in psychology. It aims to retain the most generally ac-

PREFACE Vv cepted classifications and terms, to introduce those experiments which have come into most general favor, and to leave untouched those fields in which experiment has been of doubtful value. The discussion on each topic is limited to the bearings of the experiment.

As to the method of using the book, each instructor will naturally adopt that best suited to his situation.. If space is available, the students should be encouraged to perform the experiments in the rooms of the department during certain open hours, and under the general supervision of an assistant. There should be sufficient time allowed in the recitation-period for special suggestions and directions to the students, and for reports upon the completed experiment. The students’ notes on each topic must be collected and checked rigorously ; for, no matter how explicit the directions may be, the quality of the work must be passed upon by the instruetor. It is profitable to require the students to take turns in working over the reports to show difficulties, original observations, special demonstrations, ete. Ordinarily each experiment will take two hours. The first experiment should be divided into two assignments, on account of the newness of the work and in order to avoid fatigue.

Titchener’s monumental four-volume set of laboratory manuals is a most valuable compendium.* It contains bibliographies, besides technical discussions of nearly every topic in this course. Sanford’s,f Wit-

*Titchener, “Experimental Psychology”: Qualitative (I) Student’s Manual and (II) Instructor’s Manual; Quantitative (IIT) Student’s Manual and (IV) Instructor’s Manual.

+ Sanford, “Experimental Psychology.”

vi PREFACE mer’s,* and Judd’st manuals are helpful references. Baldwin’s dictionary of Philosophy and Psychology should also be on the reference-table, together with the most approved elementary texts.

The author has gleaned material from many sources and wishes here to acknowledge his grateful obligations to those who find themselves contributors to this volume. He has had the benefit of helpful advice from many psychologists of experience ; several of them have kindly read the manuscript and made valuable suggestions. He is especially indebted to his colleague Dr. Mabel Clare Willams for cooperation.

*Witmer, “Analytical Psychology.”

+Judd, “Laboratory Manual of Psychology” and “Laboratory Equipment for Psychological Experiments.”

Contents

CHAPTER PAGE PREFACE : : ‘ : : ; : ‘ rem uil INTRODUCTION : ‘ ‘ : : : : Aaa 0:4

I. VisuaL AFTER-IMAGES ; : ; ; ‘ ‘ 1

II. Visuat CONTRAST ; ‘ ; : : 5 poms II. Tar VisuaL FIELD : ; ? : ‘ : . 28 IV. VisuaL SPACE ; ‘ § ‘ : : : ~ , 209 V. Aupirory SPACE . ‘ ; ‘ ; : : 1 1-05 Vis TActTuas, Space. : : ‘ 3 : ‘ af ea VII. Curanrots SENSATIONS : : . ‘ : a) Se VUI. Weser’s Law A : : : ‘ : ; ah Oi IX. MentrTAL IMAGES . : ‘ ‘ : : ‘ wo i04 X. ASSOCIATION . : : i ‘ ; 2 ‘ yas XI. MrEmMory : : : : ‘ ‘ ‘ : 2 ded wit: APPERCEPTION . ‘ : ‘ ; , : . 144 XITT ATTENTION . 3 ‘ : ‘ 3 ‘ : 1 os XIV. Norma. ILLUSIONS : é : ‘ : : ae

Introduction

To the Student:

PsycuoLocy is a systematic study of mental life. You now turn from the study of physical forces, rocks, flowers, and animal tissues, in nature without, to a study of your own mind. You are to perform experiments upon yourself.

The experimental method enables you to analyze and reduce a mental process to its simplest elements; to control, repeat, and vary the conditions systematically ; to record the results; to trace interrelations and explanations of known phenomena; and to discover new facts and problems.

This manual is so arranged as to furnish set exercises in which directions, aids, and explanations are given in the order needed. Only a few of the most general suggestions for your guidance need be given here.

Finish as you go along. The paragraph is the unit; always read a paragraph at a time and perform the experiment, write the report, or master the explanation before you read the next. This is mandatory, because glancing ahead would often vitiate the experiment.

Take systematic notes. The directions for notes are specific in certain minimum requirements. These notes are not primarily for the information of the instructor, or for reviews and examinations, but for the purpose ix x INTRODUCTION of clinching the observed facts and gaining practice in the recording of the results, which is an essential step in an experiment. Use loose-leaf note-books; hand in the report for each experiment to the instructor for ispection; and file the notes as they are returned.

Work intensively. Seek the most thorough insight into the problem under consideration; note new observations, test ideas suggested to you, verify and check as much as time permits. Jteason, and thus develop confidence in your own judgment and power of observation. But always adhere to the set topic. Do not ramble, or follow up the countless fascinating side lnes which come to view. Follow the directions closely, then develop your original ideas.

Apply what you learn. You will learn, for example, many laws of mental economy in this course. When you have discovered and demonstrated such laws, use them. Economize mental energy! Psychologize in your history lesson, your literature, your material science, your athletics,—wherever you are concerned with mental processes. To educate, to heal, to govern, to please, to interpret the efforts and products of the human mind; to understand inclinations, proclivities, and capacities of your own and other minds, involves knowledge of mind, which is psychology.*

*“Only with the aid of psychology can one to the fullest possible extent reap the benefits of the study of other forms of science. Language cannot be understood, literature cannot be appreciated, read, and interpreted, art cannot be profoundly comprehended, and even the natural sciences cannot have their full import revealed, without a knowledge of the mind of man.

And, indeed, how could this be otherwise, since all science itself is only the product of the human mind?” (Ladd.)

INTRODUCTION | xi

Be impartial: be not self-centered. You will be ealled upon to exhibit and measure your mental capacities In various ways, and it requires the integrity and courage of a scientist to observe and report these without bias.

Go only as far in an assignment as you can go thoroughly. One student may be able to proceed two or three times as fast as another. If you find that the lesson is too long for you, do not skim over any part, but proceed as far as you can and record the time limit.

In the experiments that follow, “For one” means that the experiments so headed may be performed by one person alone. “For two” means that two must work together, one acting as experimenter (E) and the other as observer (O). Shift in each experiment so that each one may serve in turn both as experimenter and as observer. Record which one served as observer first. Each should keep the notes which naturally go into his book according to the directions. Record also the date, the hour of the beginning of the experiment, interruptions, and any general conditions which might influence the results. Use terse language.

To experiment is to ask questions of nature. Do not simply repeat the set questions of the book, but let them open deeper and more serviceable inquiries into your mental nature. Your primary aim in this course should be, not to collect facts, but to acquire training. Carry habits of introspection, precision, analysis, and natural explanation into life and you will realize the force of our motto: Not psychology, but to psychologize.

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CHAPTER f

VISUAL AFTER-IMAGES For One.*

Most of us have observed that, if we look for a moment at a light as it is being turned out, we see an image of it a while afterward. That image is an after-image, or after-sensation. Such images manifest themselves according to traceable laws and play an important, though seldom recognized, role in our experience. We shall now make a study of some of their characteristic modes of behavior.

Success in this experiment depends mainly upon concentration of attention and economy in the use of the eyes. The eyes should not be allowed to wander aimlessly over the figures, and it 1s well to close them for rest as often as possible. Clear images can be obtained only after steady fixation. It is easier to get the after-image with one eye alone, but in the long run it is more restful to use the two eyes together.

1. Existence. a. Brightness.—Place the black square at the center of the upper half of a white sheet of paper; fixate the center of it (i.e., look intently and

*Take from the envelope the large black and gray squares, and the following small squares: black, gray, white, red, blue, yellow, green, violet, and orange. Make a pinhole at the center of each of these squares.

steadily at the pinhole) for about fifteen seconds ;* then look at the center of the lower half of the sheet of white paper and you will see a bright square, which is the after-image. Record your estimate of its relative size and duration.

b. Color.—Try the red square in the same manner. Record the color of the after-image.

An after-image is a sensory image which occurs as the result of the stimulation of a sense-organ but not until after the stimulus has been withdrawn. It is a sort of echo and bears certain relations to the object of which it is a copy as regards space, duration of the primary impression, sense quality, and intensity. Thus, in this experiment, you saw, on the surface of the blank paper, copies of the squares possibly like the original in every respect except brightnesst and color. After-images combine certain characteristics of sensations and mental images and might equally well be called after-sensations.

The causes of after-images are present in all our vision and tend to modify practically all that we see. Yet many persons live long and happily without making allowance for their distortions or even discovering the existence of them. Every object that we see leaves an impression which may bob up as an after-image, if sufficiently strong and isolated. We look at a piece of black paper and the next moment we see a copy

* A fixation-time of fifteen seconds is too long for some and too short for other observers; each will soon determine what time is most favorable for his eyes.

+ Black, white, and all the intervening grays are called brightnesses. Brightness is also present in color.

of it wherever we cast our eyes; the same is true about a light, a color, an apple, a man, a tree, a book, a house— any object which may impress the eye. The after-images in themselves are not useful, and it is fortunate that we have the instinctive power to disregard them as effectively as we do. But even though we disregard them, they modify our sensory experience and continually tone the colors, hghts, and shades of our environment.

After-images occur in all the senses, but the visual are the most conspicuous.

2, Setting.—Repeat Exp. 1 a and observe that, when the light after-image appears, there is a change in the white surface surrounding it.* Describe the change.

When we look at an object we may secure an after-image not only of that object but also of its surroundings within a limited field of vision. This complexity of the impression is one of the reasons why specific after-images are so difficult to detect and so easy to disregard.

After-images are local effects of the adaptation of the eye to changes in brightness and color. When we enter a dark room, it seems at first intensely dark, but later it assumes gray or color effects. When we pass from a dark into a light room, the light at first is dazzling, but the eye soon adapts itself so that after a while the hght does not seem so bright. During adaptation all brightnesses and all colors tend toward

*Tf the white sheet is placed against a dark background, the outline of the whole sheet may be seen in the after-image.

gray. In the above experiment a square portion of the retina is adapted to dark and the surrounding portion to light.

3. Color.—In successive trials, produce after-images of the five colors, blue, green, yellow, violet, and orange. Record the dominating color in each after-image.* Can you formulate a law for this order of color? If so, state it.

The after-image of any color goes through a series of rapid changes, possibly covering the whole spectrum ; but there is always one particular color which dominates by being the most distinct and by persisting the longest. This color is complementary to the color of the stimulus.t Of course it is modified, according to certain laws, by the color and the brightness of the background upon which it is projected.

The after-image of the dark stimulus in the first experiment was light; that is, antagonistic. We may therefore combine the observations on brightness and on color and say that the dominant color and brightness of an after-image are antagonistic to the color and brightness of the stimulus. All color after-images also involve brightness-effects. Colors are often seen in the after-images of non-colored objects.

4, Projection-background. a. Brightness-effect on Brightness.—Repeat Exp. 1 a in six successive trials

* Do not try these in too rapid succession; it may be well to intersperse them with following experiments. Beware of looking at the colors out of mere curiosity or aimlessness!

+Every color has a complementary, i.e., an opposite or antagonistic color. Colors are said to be complementary if they neutralize each other and produce gray when mixed. | under uniform conditions, except that you project the image upon different backgrounds; * namely, white, gray, and black, in the double-fatigue order.f Record the relative effectiveness of the three backgrounds.

The clearness of an image depends upon the brightness-difference between it and its projection-backeround. When projected upon the white ground, in this experiment, the hght of the image is intensified and the darkness of the surroundings is reduced by the white; on the black ground, the light of the image is minimized and the darkness of the surroundings is enhanced by the black; while, on the gray, there is a moderate interference with both image and surroundings. Hence brightness of the background makes comparatively little difference in the effectiveness of the after-image, although the brightness of the three images varies greatly. For a dark object the white projection-background is, however, usually more effective, because here the white enhances the image of the object itself, whereas on a black projection-background it is the background of the object that is enhanced.

b. Brightness-effect on Color—Repeat Exp. 1 6 in three successive trials, projecting the image upon white, eray, and black backgrounds respectively. Record the effect of the background upon the color of the after-image.

*Use the two large squares for gray and black projection-backgrounds.

+ Double-fatigue order is the technical term for the giving of a series of trials in one order and repeating them in the reverse order; thus, white, gray, black; black, gray, white. The theory is that such factors as fatigue and practice tend to even up by this order.

There is a distinct effect upon the brightness of the color; the actual color of the image mixes with the brightness of the background.

c. Color-effect on Color.—Project the after-image of the red square, in successive trials, upon the yellow, the blue, and the red square itself. Record the resulting color-effects.

The color of the after-image mixes with the color of the background. Thus, the result on the yellow is a greenish yellow; on the blue, a greenish blue; and on the red a tendency toward gray. This last trial—red upon red—explains why colors change and blur when we look intently at them; the after-image of the red disk is a pale green, and if it were projected upon a pale red of the same strength, the result would be to cancel both colors, according to the law of complementaries.

d. Absence of Background.—Fixate the black square as before, and then put your hands over your eyes and you will see the image projected somewhere into space.” Record your estimate of its size and distance and the relative effectiveness of this and the foregoing modes of projection.

The image may be projected anywhere—upon any color or brightness, upon any form, at any distance within sight. A glance at the setting sun produces shifting color-effects upon the object we look at immediately afterward; the after-image of the green leaf in

*It is usually better to keep the eyes open when covered by the hands; still, it makes but little difference whether they are open or closed, provided the covering is adequate.

a woman’s hat may be taken for a rosy blush upon her cheek.

5, Negative and Positive.—Look at a lighted lamp * for half a second, and then instantly cover the eyes and observe the radical changes in color of the after-image. Record the two dominant colors in the order of their appearance. t

The positive after-image has the same relations of brightness as the stimulus, as in a photographie positive. The negative after-image has the relations of lght and shade reversed, as in the photographic negative. The after-image may be of the same color as the stimulus, or it may be other-colored. There are positive same-colored and positive other-colored, negative same-colored and negative other-colored after-images. Generally, however, positive after-images are same-colored and negative other-colored are complementary.

The positive after-image appears first and is usually very short in duration and difficult to detect. To make it conspicuous, one must employ a strong stimulus, as in this experiment. After some training one may see the positive after-image before the negative in the exposure of ordinary objects of moderate intensity.

* Any kind: daylight does not interfere seriously.

+ Positive after-images of brightness without color may be demonstrated as follows: Face some distant object, as the branching limb of a tree outlined against a clear sky; close the eyes and cover with the hands for a minute; then open the hands and eyes for a fraction of a second, and observe, immediately after closing the eyes again, an image like the object in brightness. This is the positive after-image.

6. Size and Distance.—In three successive trials project an after-image of the black square, as in Exp. 1a, upon backgrounds at different distances from the eye; e.o;, 1 ft, 3 fti, and 10° ft. Formulate a law ot the relation between size and distance.

This variation of the size with distance shows that the after-image follows the same optical principles of projection as the normal retinal image in perception.

7. Relief.—Project an after-image of a hat, a lampglobe, or any other object that presents relief or volume. Is there any suggestion of relief or volume in the after-image ¢

The perception of relief depends upon the differences between the images in the two eyes, delicate gradations in brightness, and eye-movements, among other data. The blurred edges, the reversal of brightness, and the confusion of eye-muscle sensations militate against the perceptions of relief in the after-image. Ordinarily the after-image presents only the outline and does not suggest relief, but training and care may enable one to identify marks of relief.

8. Plasticity.—Project an after-image of the black square into an upper corner of the room. Record whether the image adapts itself to the ceiling and wallsurfaces, or retains its flat form.

It may do either; which it shall do is a matter of apperception. Usually it adapts itself plastically to the surfaces. This is particularly true if the image is projected upon some familiar surface, as the sleeve or the hand.

9. Movement.—Fixate the black square, as in Exp. 1 a, and project the image with eyes closed and covered by the hands, and try to keep the after-image directly before you. Does the image seem to move irresistibly ? If so, in what direction ?

It is clear by this time that the after-image moves with the eyes; with the eyes open, we see it in whatever direction we look. But when the eyes are closed, and we are not aware of their movement, most observers find that the image has a curiously irresistible tendency to move upward.

10. Latent Period, Duration, and Clearness.—I[n each of the following four experiments record (1) the approximate latent time,* (2) duration, and (3) relative clearness.

a. Tvme.—Project the after-image of the black square first after a fixation of five seconds and then after a fixation of. ten seconds, allowing due time for recovery between the two.

b. Brightness.—Place the black and the gray squares edge to edge upon the white sheet; fixate the adjoining edges and project the double image upon a white background. |

c. Color.—Place the red, the green, the yellow, and the blue squares in a cluster upon the white sheet ; mark

*The latent time of an after-image is the time which elapses between the withdrawal of the stimulus and the beginning of the appearance of the after-image.

+ This time should be adapted to the individual needs, the requirement being that a relatively short exposure-time shall be compared with a longer one.

a point in the center of the cluster; fixate the central point and project the four-colored after-image upon a white background.

d. Area.—Cut a piece of white paper about eight millimeters square and place it and the white square five millimeters apart upon the large black square; fixate a middle point and project the double image upon a white background.*

Long stimulation, large brightness-difference between the object and its background, and a moderately large area are conducive to a short latent time, long duration, and clearness of the after-image.t These laws are, however, subject to numerous qualifications.

These experiments merely show how it is possible to work out laws of the relation between stimuli and after-images.{ The rule is to study one factor at a time and keep all other conditions constant. The factor which is studied may be varied, as in the above separating of time, brightness, and area under controllable conditions, and the effect of such variations may be measured.

The certainty that the image shall appear depends mainly upon the exposure-time, the area, and the brightness of the stimulus, but also upon such subjective conditions as are mentioned in the following paragraph.

* A millimeter scale is printed on the last page of this book. Fold the margin of that page so as to bring the scale marking to the edge of the page.

+ The variations with color are perhaps essentially due to the difference in the brightness of the color. For this reason blue is the most effective color in this group on a white background.

t See Franz, “After-images,” The Psychological Review Monograph Supplement, Vol. ILI, No. 12.

If any one of these is inadequate the image fails to appear. As a rule, the after-image may be produced if the object is presented under such conditions as to be clearly perceptible. Thus, an electric spark, which endures only for an infinitesimal part of a second, may produce an after-image; in the present experiments the observer may not have noticed the after-image of the. white seen through the pinhole, but objects of that size may produce after-images under favorable conditions ; and one may not be able to get a distinct image of a white plate upon a white tablecloth because the brightness-difference is too small.

The duration of the after-image varies within wide limits. In extreme cases the impression has been known to persist for days and months, as with Newton, who looked at the sun with his right eye and then saw the sun continually before him for many days. The ordinary duration is, however, limited to a few seconds, and the image passes away gradually. In addition to such objective conditions as exposure-time, area, and brightness which we have noted, there are subjective factors, such as practice, expectation, attention, etc., which condition the duration.