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The Mental Life of Monkeys and Apes - A Study of Ideational Behavior
by Robert M. Yerkes
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The Mental Life of Monkeys and Apes: A Study of Ideational Behavior

ROBERT M. YERKES Harvard University



BEHAVIOR MONOGRAPHS Volume 3, Number 1, 1916 Serial Number 12 Edited by JOHN B. WATSON The Johns Hopkins University

WITH SIX PLATES AND FIVE TEXT FIGURES



CONTENTS

I. Interests, opportunity and materials

II. Observational problems and methods

III. Results of multiple-choice experiments:

1. Skirrl, Pithecus irus 2. Sobke, Pithecus rhesus 3. Julius, Pongo pygmaeus

IV. Results of supplementary tests of ideational behavior:

1. Julius, Pongo pygmaeus: Box stacking experiment Box and pole experiment Draw-in experiment Lock and key test 2. Skirrl, Pithecus irus: Box stacking experiment Box and pole experiment Draw-in experiment Hammer and nail test Other activities 3. Sobke, Pithecus rhesus: Box stacking experiment Draw-in experiment Box and pole experiment Other activities

V. Miscellaneous observations:

1. Right- and left-handedness 2. Instinct and emotion: Maternal instinct Fear Sympathy

VI. Historical and critical discussion of ideational behavior in monkeys and apes:

1. Evidences of ideation in monkeys 2. Evidences of ideation in apes

VII. Provision for the study of the primates and especially the monkeys and anthropoid apes

VIII. Bibliography



I

INTERESTS, OPPORTUNITY AND MATERIALS

Two strong interests come to expression in this report: the one in the study of the adaptive or ideational behavior of the monkeys and the apes; and the other in adequate and permanent provision for the thorough study of all aspects of the lives of these animals. The values of these interests and of the tasks which they have led me to undertake are so widely recognized by biologists that I need not pause to justify or define them. I shall, instead, attempt to make a contribution of fact on the score of each interest.

While recognizing that the task of prospecting for an anthropoid or primate station may in its outcome prove incomparably more important for the biological and sociological sciences and for human welfare than my experimental study of ideational behavior, I give the latter first place in this report, reserving for the concluding section an account of the situation regarding our knowledge of the monkeys, apes, and other primates, and a description of a plan and program for the thorough-going and long continued study of these organisms in a permanent station or research institute.

In 1915, a long desired opportunity came to me to devote myself undividedly to tasks which I have designated above as "prospecting" for an anthropoid station and experimenting with monkeys and apes. First of all, the interruption of my academic duties by sabbatical leave gave me free time. But in addition to this freedom for research, I needed animals and equipment. These, too, happily, were most satisfactorily provided, as I shall now describe.

When in 1913, while already myself engaged in seeking the establishment of an anthropoid station, I heard of the founding of such an institution at Orotava, Tenerife, the Canary Islands, I immediately made inquiries of the founder of the station, Doctor Max Rothmann of Berlin, concerning his plans (Rothmann, 1912).[1] As a result of our correspondence, I was invited to visit and make use of the facilities of the Orotava station and to consider with its founder the possibility of cooeperative work instead of the establishing of an American station. This invitation I gratefully accepted with the expectation of spending the greater part of the year 1915 on the island of Tenerife. But the outbreak of the war rendered my plan impracticable, while at the same time destroying all reasonable ground for hope of profitable cooeperation with the Germans in the study of the anthropoids. In August, 1915, Doctor Rothmann died. Presumably, the station still exists at Orotava in the interests of certain psychological and physiological research. So far as I know, there are as yet no published reports of studies made at this station. It seems from every point of view desirable that American psychologists should, without regard to this initial attempt of the Germans to provide for anthropoid research, further the establishment of a well equipped American station for the study not only of the anthropoid apes but of all of the lower primates.

[Footnote 1: See bibliography at end of report.]

In the early months of the war while I was making every effort to obtain reliable information concerning conditions in the Canary Islands, I received an urgent invitation from my friend and former student, Doctor G. V. Hamilton, to make use of his collection of animals and laboratory at Montecito, California, during my leave of absence from Harvard. This invitation I most gladly accepted, and in February, 1915, I established myself in Santa Barbara, in convenient proximity to Doctor Hamilton's private laboratory where for more than six months I was able to work uninterruptedly under nearly ideal conditions.

Doctor Hamilton without reserve placed at my disposal his entire collection of animals, laboratory, and equipment, provided innumerable conveniences for my work, and in addition, bore the entire expense of my investigation. I cannot adequately thank him for his kindness nor make satisfactory acknowledgment here of his generous aid. Thanks to his sympathetic interest and to the courtesy of the McCormick family on whose estate the laboratory was located, my work was done under wholly delightful conditions, and with assistance from Ramon Jimenez and Frank Van Den Bergh, Jr., which was invaluable. The former aided me most intelligently in the care of the animals and the construction of apparatus; and the latter, especially, was of very real service in connection with many of my experiments.

The collection of animals which Doctor Hamilton placed at my disposal consisted of ten monkeys and one orang utan. The monkeys represented either Pithecus rhesus Audebert (Macacus rhesus), Pithecus irus F. Cuvier (Macacus cynomolgos), or the hybrid of these two species (Elliot, 1913). There were two eunuchs, five males, and three females. All were thoroughly acclimated, having lived in Montecito either from birth or for several years. The orang utan was a young specimen of Pongo pygmaeus Hoppius obtained from a San Francisco dealer in October, 1914 for my use. His age at that time, as judged by his size and the presence of milk teeth, was not more than five years. So far as I could discover, he was a perfectly normal, healthy, and active individual. On June 10, 1915, his weight was thirty-four pounds, his height thirty-two inches, and his chest girt twenty-three inches. On August 18 of the same year, the three measurements were thirty-six and one-half pounds, thirty-three inches, and twenty-five inches.

For the major portion of my experimental work, only three of the eleven animals were used. A growing male, P. rhesus monkey, known as Sobke; a mature male, P. irus, called Skirrl; and the young orang utan, which had been named Julius. Plates I and II present these three subjects of my experiments in characteristically interesting attitudes. In plate I, figure 1, Julius appears immediately behind the laboratory seated on a rock, against a background of live oaks. This figure gives one an excellent idea of the immediate environment of the laboratory. Figure 2 of the same plate is a portrait of Julius taken in the latter part of August. By reason of the heavy growth of hair, he appeared considerably older as well as larger at this time than when the photograph for figure 1 was taken. In plate II, figure 3, Julius is shown in the woods in the attitude of reaching for a banana, while in figure 4 of the same plate he is represented as walking upright in one of the cages.

Likenesses of Sobke are presented in figures 5 and 6 of plate II. In the latter of these figures he is shown stretching his mouth, apparently yawning but actually preparing for an attack on another monkey behind the wire screen. Figure 7 of this plate indicates Skirrl in an interesting attitude of attention and with an obvious lack of self-consciousness. The same monkey is represented again in figures 8 and 9 of plate II, this time in the act of using hammer and saw.

EXPLANATION OF PLATE II

FIGURE 3.—Orang utan, Julius, reaching for banana.

FIGURE 4.—Julius walking across his cage.

FIGURE 5.—P. rhesus, Sobke.

FIGURE 6.—Sobke stretching his jaws (yawn?) preparatory to a fight.

FIGURE 7.—P. irus, Skirrl.

FIGURE 8.—Skirrl using hammer and nail.

FIGURE 9.—Skirrl using a saw.



All of the animals except the orang utan had been used more or less for experiments on behavior by Doctor Hamilton, but this prior work in no way interfered with my own investigation. Doctor Hamilton has accumulated a large mass of the most valuable and interesting observations on the behavior of monkeys, and he more thoroughly understands them than any other observer of whom I have knowledge. Much to my regret and embarrassment in connection with the present report, he has thus far published only a small portion of his data (Hamilton, 1911, 1914). In his most recent paper on "A study of sexual tendencies in monkeys and baboons," he has given important information concerning several of the monkeys which I have observed. For the convenience of readers who may make use of both his reports and mine, I am designating the animals by the names previously given them by Hamilton. The available and essential information concerning the individuals is presented below.



List of animals in collection

Skirrl. Pithecus irus. Adult male.

Sobke. P. rhesus. Young adult male.

Gertie. P. irus-rhesus. Female. Born November, 1910.

Maud. P. rhesus. Young adult female.

Jimmy II. P. irus. Adult male.

Scotty. P. irus (?). Adult male.

Tiny. P. irus-rhesus. Female. Born August, 1913.

Chatters. P. irus. Adult eunuch.

Daddy. P. irus. Adult eunuch.

Mutt. P. irus. Young adult male. Born August, 1911.

Julius. Pongo pygmaeus. Male. Age, 4 years to 5 years.



When I arrived in Santa Barbara, Doctor Hamilton was about to remodel, or rather reconstruct, his animal cages and laboratory. This gave us opportunity to adapt both to the special needs of my experiments. The laboratory was finally located and built in a grove of live oaks. From the front it is well shown by figure 10 of plate III, and from the rear, by figure 11. Its location was in every way satisfactory for my work, and in addition, the spot proved a delightful one in which to spend one's time.



Figure 12 is a ground plan, drawn to scale, of the laboratory and the adjoining cages, showing the relations of the several rooms of the laboratory among themselves and to the nine cages. Although the construction was throughout simple, everything was convenient and so planned as to expedite my experimental work. The large room A, adjoining the cages, was used exclusively for an experimental study of ideational behavior by means of my recently devised multiple-choice method. Additional, and supplementary, experiments were conducted in the large cage Z. Room D served as a store-room and work-shop.

The laboratory was forty feet long, twenty-two feet wide, and ten feet to the plate. Each small cage was six, by six, by twelve feet deep, while the large compartment into which each of the smaller cages opened was twenty-four feet long, ten feet wide, and twelve feet deep.



II

OBSERVATIONAL PROBLEMS AND METHODS

My chief observational task in Montecito was the study of ideational behavior, or of such adaptive behavior in monkeys and apes as corresponds to the ideational behavior of man. It was my plan to determine, so far as possible in the time at my disposal, the existence or absence of ideas and the role which they play in the solution of problems by monkeys and apes. I had in mind the behavioristic form of the perennial questions: Do these animals think, do they reason, and if so, what is the nature of these processes as indicated by the characteristics of their adaptive behavior?

My work, although obviously preliminary and incomplete, differs from most of the previous studies of the complex behavior of the infrahuman primates in that I relied chiefly upon a specially devised method and applied it systematically over a period of several months. The work was intensive and quantitative instead of more or less incidental, casual, and qualitative as has usually been the case. Naturally, during the course of my special study of ideational behavior observations were made relative to various other aspects of the life of my subjects. Such, for example, are my notes on the use of the hands, the instincts, the emotions, and the natural aptitudes of individuals. It is, indeed, impossible to observe any of the primates without noting most interesting and illuminating activities. And although the major portion of my time was spent in hard and monotonous work with my experimental apparatus, I found time each day to get into intimate touch with the free activities of my subjects and to observe their social relations and varied expressions of individuality. As a result of my close acquaintance with this band of primates, I feel more keenly than ever before the necessity of taking into account, in connection with all experimental analyses of behavior, the temperamental characteristics, experience, and affective peculiarities of individuals.

The light which I have obtained on the general problem of ideation has come, first, through a method which I have rather inaptly named the multiple-choice method, and second, and more incidentally, through a variety of supplementary methods which are described in Section IV of this report. These supplementary methods are simple tests of ideation rather than systematic modes of research. They differ from my chief method, among other respects, in that they have been used by various investigators during the past ten or fifteen years. It was not my aim to repeat precisely the observations made by others, but instead to verify some of them, and more especially, to throw additional light on my main problem and to further the analysis of complex behavior.

What has been referred to as the multiple-choice method was devised by me three years ago as a means of obtaining strictly comparable objective data concerning the problem-solving ability of various types and conditions of animals. The method was first tried with human subjects in the Psychopathic Hospital, Boston, with a crude keyboard apparatus which, however, proved wholly satisfactory as a means of demonstrating its value. It has since been applied by means of mechanisms especially adapted to the structure and activities of the organisms, to the study of the behavior of the crow, pig, rat, and ringdove (Yerkes, 1914; Coburn and Yerkes, 1915; Yerkes and Coburn, 1915). The method has also been applied with most gratifying results to the study of the characteristics of ideational behavior in human defectives,—children, and adults,—and in subjects afflicted with various forms of mental disease. It is at present being tried out as a practical test in connection with vocational guidance and various forms of institutional examination, such as psychopathic hospital and court examinations.

As no adequate description of the method has yet been published to which I can here refer, it will be necessary to present its salient characteristics along with a description of the special form of apparatus which was found suitable for use with monkeys and apes.

The method is so planned as to enable the observer to present to any type or condition of organism which he wishes to study any one or all of a series of problems ranging from the extremely simple to the complex and difficultly soluble. All of the problems, however, are completely soluble by an organism of excellent ideational ability. For the human subject, the solution of the easiest problem of all requires almost no effort, whereas even moderately difficult problems may require many repetitions of effort and hours or days of application to the task. In each case, the solution of the problem depends upon the perception of a certain constant relation among a series of objects to which the subject is required to attend and respond. Such relations are, for example, secondness from one end of the group, middleness, simple alternation of ends, or progressive movement by constant steps from one end of a group to the other.

It is possible to present such relational problems by means of relatively simple reaction-mechanisms. In their essential features, all of the several types of multiple-choice apparatus designed by the writer and used either by him or by his students and assistants are the same. They consist of a series of precisely similar reaction-devices, any one or all of which may be used in connection with a given observation. These reaction-mechanisms are so chosen as to be suited to the structure and action-system of the animal to be studied. For the human being the mechanism consists of a simple key and the total apparatus is a bank of keys, with such electrical connections as are necessary to enable the observer to obtain satisfactory records of the subject's behavior. Let us suppose the bank of keys, as was actually the case in my first form of apparatus, to consist of twelve separate reaction-mechanisms; and let us suppose, further, the constant relation (problem) on the basis of which the subject is required to react to be that of middleness. It is evident that in successive trials or experiments the keys must be presented to the subject in odd groups, the possibilities being groups of 3, 5, 7, 9, or 11. If for a particular observation the experimenter wishes to present the first three keys at the left end of the keyboard, he pushes back the remaining nine keys so that they cannot be operated and requires the subject to select from the group of three keys the one which on being pressed causes a signal to appear. It is of course the clearly understood task of the subject to learn to select the correct key in the group on first trial. This becomes possible only as the subject observes the relation of the key which produces the desired effect to the other keys in the group. On the completion of a subject's reaction to the group of three keys, a group of seven keys at the opposite end of the keyboard may, for example, be presented. Similarly, the subject is required to discover with the minimum number of trials the correct reaction-mechanism. Thus, time after time, the experimenter presents a different group of keys so that the subject in no two successive trials is making use of the same portion of the keyboard. It is therefore impossible for him to react to spatial relations in the ordinary sense and manner, and unless he can perceive and appropriately respond to the particular relation which constitutes the only constant characteristic of the correct reaction-mechanism for a particular problem, he cannot solve the problem, or at least cannot solve it ideationally and on the basis of a small number of observations or trials.

For the various infrahuman animals whose ideational behavior has been studied by means of this method, it has been found eminently satisfactory to use as reaction-mechanisms a series of similar boxes, each with an entrance and an exit door. An incentive to the selection of the right box in a particular test is supplied by food, a small quantity of which is placed in a covered receptacle beyond the exit door of each of the boxes. Each time an animal enters a wrong box, it is punished for its mistake by being confined in that box for a certain period, ranging from five seconds to as much as two minutes with various individuals or types of organism. This discourages random, hasty, or careless choices. When the right box is selected, the exit door is immediately raised, thus uncovering the food, which serves as a reward. After eating the food thus provided, the animal, according to training, returns to the starting point and eagerly awaits an opportunity to attempt once more to find the reward which it has learned to expect. With this form of the apparatus, the boxes among which choice may be made are indicated by the raising (opening) of the front door.

Since with various birds and mammals the box form of apparatus had proved most satisfactory, I planned the primate apparatus along similar lines, aiming simply to adapt it to the somewhat different motor equipment and destructive tendencies of the monkeys. I shall now briefly describe this apparatus as it was constructed and used in the Montecito laboratory.



EXPLANATION OF PLATE IV

FIGURE 13.—Multiple-choice apparatus, showing observer's bench and writing stand. FIGURE 14.—Apparatus as seen from observer's bench. FIGURE 15.—Entrances to multiple-choice boxes as seen from the response-compartment. FIGURE 16.—Apparatus as seen from the rear, showing exit doors, food receptacles, and covers for same.



The apparatus was built in room A (figure 12), this room having been especially planned for it with respect to lighting as well as dimensions and approaches. It was unfortunately impossible to obtain photographs showing the whole of the apparatus, but it is hoped that the four partial views of plate IV may aid the reader who is unfamiliar with previously described similar devices to grasp readily the chief points of construction. In this plate, figure 13 shows the front of the complete apparatus, with the alleyway and door by way of which the experimenter could enter. The investigator's observation-bench and record-table also appear in this figure, together with weighted cords used to operate the various doors and the vertically placed levers by means of which each pair of doors could be locked. Figure 14 is the view presented to the observer as he stood on the bench or observation stand of figure 13 and looked over the entire apparatus. Three of the entrance doors are shown at the right of this figure as raised, whereas the remainder of the nine entrance doors of the apparatus are closed. Figure 15 is a view of the entrance doors from below the wire roof of the apparatus. Again, two of the doors are shown as raised, and three additional ones as closed. The rear of the apparatus appears in figure 16, in which some of the exit doors are closed and others open. In the latter case, the food receptacles appear, and on the lower part of the raised doors of the corresponding boxes may be seen metal covers for the food receptacles projecting at right angles to the doors, while on the lower edge of each door is an iron staple used to receive a sliding bar which could be operated from the observer's bench as a means of locking the doors after they had been closed. The space beyond the exit doors was used as an alleyway for the return of the animals to the starting point.

It will be necessary at various points in later descriptions to refer to these several figures. But further description of them will be more readily appreciated after a careful examination of the ground plan of the apparatus presented as figure 17 In accordance with the labelling of this figure, the experimenter enters the apparatus room through doorway 16, passes thence through doorways 17 and 10 to the large cage Z, from which he has direct access to the animals and can bring them into the apparatus. The multiple-choice mechanism proper, consisting of nine similar boxes (nine were used instead of twelve as a matter of convenience of construction, not because this smaller number is otherwise preferable) is labelled F. These boxes are numbered 1 to 9, beginning at the left. This numbering was adhered to in the recording of results throughout the investigation. The other important portions of the apparatus are the runway D, from which the subject at the experimenter's pleasure could be admitted through doorway 12 to the large response-chamber E; the alleyways G, H, and I, by way of which return to the starting point was possible; the observation bench C, with its approach step 13; and the observer's writing table A.

In the construction of this large apparatus, it was necessary to make provision for the extremely destructive tendencies of monkeys and anthropoid apes,—hence the apparent cumbersomeness of certain portions. It was equally necessary to provide for the protection of the observer and the prevention of escape of the subjects by completely covering the apparatus and alleyways with a heavy wire netting.

Each of the eighteen doors of the multiple-choice boxes, and in addition doors 11, 12, and 15 of the runway D, were operated by the observer from his bench C by means of weighted window cords which were carried by pulleys appropriately placed above the apparatus. Each weight was so chosen as to be just sufficient to hold its door in position after the experimenter had raised it. For the convenience of the experimenter in the rapid operation of the twenty-one doors, the weights for the doors of runway D were painted gray, those for the entrance doors, white, and those for the exit doors, black.

In each entrance door, as is shown in figure 15 of plate IV, a window was cut so that the experimenter might watch the animal after it had entered a given box, and especially note when it left the box after having received its reward. This window was covered with wire netting. No such windows were necessary in the exit doors, but to them were attached heavy galvanized iron flanges which served to cover the food receptacles. One of these flanges is labelled o in figure 17. The food receptacles were provided by boring holes in a 2 by 4 inch timber securely nailed to the floor immediately outside of the exit doors. Into these holes aluminum cups fitted snugly, and the iron flanges, when the doors were closed, fitted so closely over the cups that it was impossible for the animals to obtain food from them.



As originally constructed, no provision was made in the apparatus for locking the entrance and exit doors of the several boxes when they were closed. But as two of the subjects after a time learned to open the doors from either outside or inside the boxes, it became necessary to introduce locking devices which could be operated by the experimenter from the observation bench. This was readily accomplished by cutting holes in the floor, which permitted an iron staple, screwed to the lower edge of each door, to project through the floor. Through these staples by means of a lever for each of the nine boxes, the observer was able to slide a wooden bar, placed beneath the floor of the room, thus locking or unlocking either the entrance door, the exit door, or both, in the case of any one of the nine boxes.

Since figure 17 is drawn to scale, it will be needless to give more than a few of the dimensions of the apparatus. Each of the boxes was 42 inches long, 18 inches wide, and 72 inches deep, inside measurements. The alleys D, I, and H were 24 inches, and G 30 inches wide, by 6 feet deep. The doors of the several boxes were 18 inches wide, by 5 feet high, while those in the alleyways were 24 inches wide by 6 feet high. The response-compartment E of figure 17 was 14 feet 4 inches, by 8 feet, by 6 feet in depth. In order that the apparatus might be used with adult human subjects conveniently, if such use should prove desirable, the depth throughout was made 6 feet, and it was therefore possible for the experimenter to walk about erect in it.

The experimental procedure was briefly as follows: A small quantity of food having been placed in each of the food cups and covered by the metal flanges on the exit doors, the experimenter raised door 11 of figure 17 and then opened door 10 and the door of the cage in which the desired subject was confined. After the latter, in search of food, had entered the runway D, the experimenter lowered door 11 to keep it in this runway, and immediately proceeded to set the reaction-mechanisms for an experiment (trial). Let us suppose that the first setting to be tried involved all of the nine boxes. Each of the entrance doors would therefore be raised. Let us further suppose that the right door is defined as the middle one of the group. With the apparatus properly set, the experimenter next raises door 12, thus admitting the animal to the response-compartment E. Any one of the nine boxes may now be entered by it. But if any except number 5, the middle member of the group, be entered, the entrance door is immediately lowered and both the exit and entrance doors locked in position so that the animal is forced to remain in the box for a stated period, say thirty seconds. At the expiration of this time the entrance door is raised and the animal allowed to retrace its steps and make another choice. When the middle box is chosen, the entrance door is lowered and the exit door immediately raised, thus uncovering the food, which the animal eats. As a rule, by my monkeys and ape the reward was eaten in the alleyway G instead of in the multiple-choice box. As soon as the food has been eaten, the exit door is lowered by the experimenter, and the animal returns by way of G and H to runway D, where it awaits its next trial.

As rewards, bananas and peanuts were found very satisfactory, and although occasionally other foods were supplied in small quantities, they were on the whole less constantly desired than the former.

Four problems which had previously been presented to other organisms were in precisely the same form presented to the three primates. These problems may be described, briefly, by definition of the right reaction mechanism, thus: problem 1, the first mechanism at the subject's left; problem 2, the second mechanism at the subject's right (that is, from the end of the series at the subject's right); problem 3, alternately, the first mechanism at the subject's left and the first at its right; problem 4, the middle mechanism of the group.

It was my intention to present these four problems, in order, to each of the three animals, proceeding with them as rapidly as they were solved. But as it happened, only one of the three subjects got as far as the fourth problem. When observations had to be discontinued, Sobke was well along with the last, or fourth problem; Skirrl was at work at the third problem; and Julius had failed to solve the second problem.

For each of the problems, a series of ten different settings of the doors was determined upon in advance. These settings differ from those employed in a similar investigation with the pig only in that the numbering of the doors is reversed. In the present apparatus, the boxes as viewed from the front (entrance) are numbered from the left to the right end, whereas those of the pig apparatus were numbered from the right end to the left end.

Below are presented for each of the several problems (1) the numbers of the settings presented in series; (2) the numbers of the doors open; (3) the number of doors open in each setting and for the series of ten settings; and (4) the number of the right door.



PROBLEM 1. First mechanism at left of group

Doors No. of No. of Settings open doors open right door 1..................1.2.3......................3..................1 2..................8.9........................2..................8 3..................3.4.5.6.7..................5..................3 4..................7.8.9......................3..................7 5..................2.3.4.5.6..................5..................2 6..................6.7.8......................3..................6 7..................5.6.7......................3..................5 8..................4.5.6.7.8..................5..................4 9..................7.8.9......................3..................7 10..................1.2.3......................3..................1 — Total 35

PROBLEM 2. Second mechanism from the right end of group

Doors No. of No. of Settings open doors open right door 1..................7.8.9......................3..................8 2..................1.2.3.4....................4..................3 3..................2.3.4.5.6.7................6..................6 4..................1.2.3.4.5.6................6..................5 5..................4.5.6.7.8..................5..................7 6..................1.2.3......................3..................2 7..................2.3.4.5....................4..................4 8..................1.2.3.4.5.6.7.8.9..........9..................8 9..................1.2.3.4....................4..................3 10..................3.4.5.6.7.8................6..................7 — Total 50

PROBLEM 3. Alternately the first mechanism at the left and the first at the right end of the group

Doors No. of No. of Settings open doors open right door 1..................5.6.7......................3..................5 2..................5.6.7......................3..................7 3..................1.2.3.4.5.6................6..................1 4..................1.2.3.4.5.6................6..................6 5..................4.5.6.7.8..................5..................4 6..................4.5.6.7.8..................5..................8 7..................2.3.4.5....................4..................2 8..................2.3.4.5....................4..................5 9..................3.4.5.6.7.8.9..............7..................3 10..................3.4.5.6.7.8.9..............7..................9 — Total 50

PROBLEM 4. Middle mechanism of the group

Doors No. of No. of Settings open doors open right door 1..................2.3.4......................3..................3 2..................5.6.7.8.9..................5..................7 3..................1.2.3.4.5.6.7..............7..................4 4..................7.8.9......................3..................8 5..................4.5.6.7.8..................5..................6 6..................1.2.3.4.5.6.7.8.9..........9..................5 7..................1.2.3......................3..................2 8..................2.3.4.5.6..................5..................4 9..................3.4.5.6.7.8.9..............7..................6 10..................6.7.8......................3..................7 — Total 50



It was found desirable after a problem had been solved to present a new and radically different series of settings in order to determine to what extent the subject had learned to choose the correct door by memorizing each particular setting. These supplementary observations may be known as control experiments, and the settings as supplementary settings. In case of these, as for the original settings, the essential facts are presented in tabular arrangement.



Settings for Control Experiments

PROBLEM 1. First at left end

Doors No. of No. of Settings open doors open right door 1..................2.3.4......................3..................2 2..................6.7.8.9....................4..................6 3..................3.4.5......................3..................3 4..................4.5.6.7.8.9................6..................4 5..................6.7.8.9....................4..................6 6..................1.2.3.4.5..................5..................1 7..................2.3.4.5.6.7.8..............7..................2 8..................3.4.5.6.7.8................6..................3 9..................5.6.7......................3..................5 10..................1.2.3.4.5.6.7.8.9..........9..................1

PROBLEM 2. Second from right end

Doors No. of No. of Settings open doors open right door 1..................5.6.7.8....................4..................7 2..................2.3.4.5.6..................5..................5 3..................1.2.3.4.5.6.7.8.9..........9..................8 4..................5.6.7......................3..................6 5..................1.2.3.4....................4..................3 6..................4.5.6......................3..................5 7..................2.3.4.5....................4..................4 8..................1.2.3......................3..................2 9..................1.2.3.4.5.6.7..............7..................6 10..................2.3.4.5.6.7.8.9............8..................8

PROBLEM 3. Alternate left and right ends

Doors No. of No. of Settings open doors open right door 1..................5.6........................2..................5 2..................5.6........................2..................6 3..................4.5.6.7.8.9................6..................4 4..................4.5.6.7.8.9................6..................9 5..................1.2.3.4.5..................5..................1 6..................1.2.3.4.5..................5..................5 7..................2.3.4.5.6.7................6..................2 8..................2.3.4.5.6.7................6..................7 9..................3.4.5.6.7.8................6..................3 10..................3.4.5.6.7.8................6..................8

PROBLEM 4. Middle

Doors No. of No. of Settings open doors open right door 1..................4.5.6.7.8..................5..................6 2..................1.2.3......................3..................2 3..................1.2.3.4.5.6.7.8.9..........9..................5 4..................2.3.4.5.6..................5..................4 5..................6.7.8......................3..................7 6..................3.4.5.6.7.8.9..............7..................6 7..................7.8.9......................3..................8 8..................1.2.3.4.5.6.7..............7..................4 9..................2.3.4......................3..................3 10..................3.4.5.6.7..................5..................5



It was my aim so far as possible to present to a given subject each day the ten settings under a given problem in order, without interruption. If for any reason the series of observations had to be interrupted, it was resumed at the same point subsequently. Occasionally it was found desirable or necessary to present only five of the series of ten settings in succession and then to interrupt observations for an interval of a few minutes or even several hours. But as a rule it was possible to present the series of ten settings. All things being considered, it proved more satisfactory to give only ten trials a day to each subject. Frequently twenty and rarely thirty trials were given on the same day. In such cases the series of settings was simply repeated. The only pause between trials was that necessary for resetting the entrance doors and replenishing the food which served as a reward for success.



III

RESULTS OF MULTIPLE-CHOICE EXPERIMENTS

1. Skirrl, Pithecus irus

Problem 1. First at the Left End

Systematic work with the multiple-choice apparatus and method described in the previous section was undertaken early in April with Skirrl, Sobke, and Julius. The results for each of them are now to be presented with such measure of detail as their importance seems to justify.

Skirrl had previously been used by Doctor Hamilton in an experimental study of reactive tendencies. He proved so remarkably inefficient in the work that Doctor Hamilton was led to characterize him as feeble-minded, and to recommend him to me for further study because of his mental peculiarities. With me he was from the first frank, aggressive, and inclined to be savage. It was soon possible for me to go into the large cage, Z, with him and allow him to take food from my hand. He was without fear of the experimental apparatus and it proved relatively easy to accustom him to the routine of the experiment. Throughout the work he was rather slow, inattentive, and erratic.

Beginning on April 7, I sought to acquaint him with the multiple-choice apparatus by allowing him to make trips through the several boxes, with the reward of food each time. Thus, for example, with the entrance and exit doors of box 7 raised, the monkey was allowed to pass into the reaction-compartment E and thence through box 7 to the food cup. As soon as he had finished eating, he was called back to D by the experimenter and, after a few seconds, allowed, similarly, to make a trip by way of one of the other boxes. By reason of this preliminary training he soon came to seek eagerly for the reward of food.

On April 10 the apparatus was painted white in order to increase the lightness and thus render it easier for the experimenter to observe the animal's movements, and when on April 12 Skirrl was again introduced to it for further preliminary training, he utterly refused to enter the boxes, giving every indication of extreme fear of the white floors and even of the sides of the boxes. Finally, the attempts to induce him to enter the boxes had to be given up, and he was returned to his cage unfed. The following day I was equally unsuccessful in either driving or tempting him with food into the apparatus. But on April 14 he was so hungry that he was finally lured in by the use of food. He cautiously approached the boxes and attempted to climb through on the sides instead of walking on the floor. It was perfectly evident that he had an instinctive or an acquired fear of the white surfaces. As the matter was of prime importance for the success of my work, I inquired of Doctor Hamilton, and of the men in charge of the cages, for any incident which might account for this peculiar behavior, and I learned that some three months earlier, while the animal cages were being whitewashed, Skirrl had jumped at one of the laborers who was applying a brush to the framework of one of the cages and had shaken some lime into his eyes. He was greatly frightened and enraged. Evidently he experienced extreme discomfort, if not acute pain, and there resulted an association with whiteness which was quite sufficient to cause him to avoid the freshly painted apparatus.

Having obtained an adequate explanation of this monkey's peculiar behavior, I proceeded with my efforts to induce him to work smoothly and rapidly, and on April 15, by covering the floor with sawdust, I so diminished the influence of the whiteness as to render the preliminary training fairly satisfactory. At the end of two more days everything was going so well that it seemed desirable to begin the regular experiment.

On the morning of April 19, Skirrl was introduced to the apparatus and given his first series of ten trials on problem 1. This problem demanded the selection of the first door at the left in any group of open doors. The procedure was as previously described in that the experimenter raised the entrance doors of a certain group of boxes, admitted the animal to the reaction-chamber, punished incorrect choices by confining the animal for thirty seconds, and rewarded correct choices by raising the exit door and thus permitting escape and the obtaining of food. The trials were given in rapid succession, and the total time required for this first series of ten trials was thirty-five minutes. Skirrl worked faithfully throughout this interval and exhibited no marked discouragement. When confined in a box he showed uneasiness and dissatisfaction by moving about constantly, shaking the doors, and trying to raise them in order to escape.

For the series of settings used in connection with problem 1, the reader is referred to page 18. In the first setting, the doors numbered 1, 2, and 3, were opened. As it happened, the animal when admitted to the reaction-chamber immediately chose box l. Having received the reward of food, he was called back to D, and doors 8 and 9 having been raised in preparation for the next trial, he was again admitted to the reaction-chamber. This time he quickly chose box 9 and was confined therein for thirty seconds. On being released, he chose after an interval of four minutes, box 8, thus completing the trial.

As it is highly important, not only in connection with the present description of behavior, but also for subsequent comparison of the reactions of different types of organism in this experiment, to present the detailed records for each trial, tables have been constructed which offer in brief space the essential data for every trial in connection with a given problem.

Table 1 contains the results for Skirrl in problem 1. It is constructed as follows: the date of a series of trials appears in the first vertical column; the numbers (and number) of the trials for the series or date appear in column 2; the following ten columns present respectively the results of the trials for each of the ten settings. Each number, in these results, designates a box entered. At the extreme right of the table are three columns which indicate, first, the number of trials in which the right box was chosen first, column headed R; and second, the number of trials in which at least one incorrect choice occurred, column headed W. In the last column, the daily ratio of these first choices appears.

Taking the first line of table 1 below the explanatory headings, we note on April 19 ten trials, numbered 1 to 10, were given to Skirrl. In trial 1, with setting 1, he chose correctly the first time, and the record is therefore simply 1. In trial 2, setting 2, he incorrectly chose box 9, the first time. At his next opportunity, he chose box 8, which was the right one. The record therefore reads 9.8. In trial 3, setting 3, he chose incorrectly twice before finally selecting the right box. The record reads 6.7.3, and so on throughout the ten trials which constitute a series. The summary for this series indicates three right and seven wrong first choices, that is, three cases in which the right box was entered first. The ratio of right to wrong first choices is therefore 1 to 2.33. Since the total number of doors open in the ten settings is thirty-five, and since in each of the ten settings one door is describable as the right door, the probable ratio, apart from the effects of training, of right to wrong first choices is 1 to 2.50. It is evident, therefore, that Skirrl in his first series of trials closely approximated expectation in the number of mistakes.



TABLE 1

Results for Skirrl, P. irus, in Problem 1

========+========+======+========+==========+============+==========+==========+==========+============+==========+==========+==+==+======== No. S.1 S.2 S.3 S.4 S.5 S.6 S.7 S.8 S.9 S.10 Ratio Date of R W of trials 1.2.3 8.9 3.4.5.6.7 7.8.9 2.3.4.5.6 6.7.8 5.6.7 4.5.6.7.8 7.8.9 1.2.3 R to W + + -+ -+ -+ -+ -+ -+ -+ -+ -+ -+ -+ -+ April 19 1- 10 1 9.8 6.7.3 9.7 6.2 7.8.6 {6.7.7.7 4 7 2.3.3.1 3 7 1:2.33 {6.5 20 11- 20 3.2.1 9.8 5.3 7 4.2 8.8.6 5 8.4 7 3.1 3 7 1:2.33 21 21- 30 3.1 8 3 8.7 6.2 6 5 6.4 9.7 1 5 5 1:1.00 22 31- 40 1 9.8 3 7 6.2 6 6.7.5 5.8.4 9.8.9.8.7 2.1 4 6 1:1.50 23 41- 50 2.3.1 8 5.7.3 7 4.2 6 5 7.8.4 7 3.1 5 5 1:1.00 24 51- 60 1 8 4.5.7.3 9.7 5.6.2 6 6.7.5 6.4 8.9.7 1 4 6 1:1.50 26 61- 70 1 8 6.7.4.7.3 7 4.5.6.2 6 5 8.4 7 3.2.3.1 6 4 1: .67 27 71- 80 3.1 8 3 9.7 4.6.2 7.6 6.5 5.8.4 7 1 4 6 1:1.50 28 81- 90 2.3.1 8 3 7 4.5.6.2 6 5 5.8.4 7 1 7 3 1: .43 29 91- 100 1 8 3 9.7 6.2 6 5 4 7 1 8 2 1: .25 30 101- 110 1 8 4.3 7 5.6.2 6 5 4 7 2.3.1 7 3 1: .43 May 1 111- 120 2.3.2.1 8 3 7 2 6 5 4 7 1 9 1 1: .11 3 121- 130 1 8 5.6.3 7 4.5.2 6 5 4 7 1 8 2 1: .25 4 and 5 131- 140 3.2.1 8[1] 3 7 2 6 5 4 7 1 9 1 1: .11 5 141- 150 1 8 4.3 7 2 6 5 4 7 1 9 1 1: .11 + + -+ -+ -+ -+ -+ -+ -+ -+ -+ -+ -+ -+ 2.3.4.5 1.2.3.4.5 2.3.4 6.7.8.9 3.4.5 4.5.6.7.8.9 6.7.8.9 1.2.3.4.5 6.7.8 3.4.5.6.7.8 5.6.7 6.7.8.9 + -+ -+ -+ -+ -+ -+ -+ -+ -+ -+ -+ -+ 6 1- 10 2 6 3 4 6 3.2.1 6.2 5.6.7.8.3 5 6.1 6 4 1: .67 ======+========+========+========+==========+============+==========+==========+==========+============+==========+==========+==+==+========

[Footnote 1: End of series on May 4.]



By reading downward in any particular column of results, one obtains a description of the changes in the animal's reaction to a particular setting of the doors. Thus, for instance, in the case of setting 1, which was presented to the animal in trials numbered 1, 11, 21, and so on to 141, it is clear from the records that no definite improvement occurred. But oddly enough, in the case of setting 10, which presented the same group of open doors, almost all of the reactions are right in the lower half of the column. For setting 2, it is evident that mistakes soon disappeared.

Comparison of the data of table 1 indicates that the number of correct first choices is inversely proportional to the number of doors in use, while the number of choices made in a given trial is directly proportional to the number of doors in use.

During the first week of work on this problem, Skirrl improved markedly. His performance was somewhat irregular and unpredictable, but on the whole the experiment seemed fairly satisfactory. Cold, cloudy, or rainy days tended to diminish steadiness and to increase the number of mistakes. Similarly, absence of hunger was unfavorable to continuous effort to find the right box.

The period of confinement, as punishment for wrong choices, was increased from thirty seconds to sixty seconds on April 26. But there is no satisfactory evidence that this favored the solution of the problem. Work on May 4 was interrupted by a severe storm, the noise of which so distracted the monkey that he ceased to work. Consequently, observations were interrupted on the completion of trial 132, and on May 5, the series was begun with setting 3. On this date, eighteen trials were given in succession, and in only one of them did a mistake occur. Since the ten trials numbered 133 to 142 were correct, Skirrl was considered to have solved problem 1, and systematic training was discontinued.

On the following day, as a measure of the extent to which the animal had learned to select the first door at the left no matter what its position or the number of doors in the group presented, a control series was given in which the settings differed from the regular series of settings. These supplementary settings are presented at the bottom of table 1 together with the records of reaction in ten trials.

Since in only six of these ten control settings was the first choice correct, it is scarcely fair to insist that the animal was reacting on the basis of an ideational solution of the problem. Rather, it would seem that he had learned to react to particular settings. A careful study of all of the data of response, together with notes on the varied behavior of the animal during the experiments, justifies the statement that Skirrl's solution of problem 1 was incomplete and unreliable. It was highly dependent upon the particular situation, or even the particular door at the left end of the group, and slightly if at all dependent upon anything comparable to the human idea of first at the left of the group.

This particular series of observations has been described and discussed in some detail in order to make the chief points of method clear. It will be needless, hereafter, to refer explicitly to many of the characteristics of reaction or to the important points in the construction of tables which have been mentioned.

A graphic representation of Skirrl's learning process in problem 1 is presented in figure 18. The irregularities are most striking, and fairly indicate the erraticness of the animal. The curve is based upon the data in next to the last column of table 1, that is, the column presenting the errors or wrong first choices in each series of trials.

Unquestionably, the form of such a curve of learning should be considered in connection with the method or methods of selecting the right box employed by the animal during the course of experimentation. It appears from an analysis of the behavior of Skirrl in problem 1 that there developed a single definite and persistent method, namely, that of going to one box in the group, and in case it happened to be a wrong one, of choosing, on emergence from it, the next toward the right end of the group, and so on down the line. Having reached the extreme right end, the tendency was to follow the side of the reaction-chamber around to the opposite end and to enter the first box at the left end of the group, which was, of course, the right one. This method appears, with certain slight variations, in approximately ninety per cent of the trials which involved incorrect choices. Thus, in the case of trials 121 to 130, of which eight exhibit right first choices, the remaining two exhibit the method described above except that the final member at the right end of the group was in each case omitted.



On the whole, Skirrl's behavior in connection with this problem appears to indicate a low order of intelligence. He persisted in such stupid acts as that of turning, after emergence from the right box, toward the right and passing into the blind alley I, instead of toward the left, through G and H, to D. In contrast with the other animals, he spent much time before the closed doors of the boxes, instead of going directly to the open doors, some one of which marked the box in which the reward of food could be obtained. It is, moreover, obvious that his responses, as they appear in table 1, are extremely different from those of a human being who is capable of bringing the idea of first at the left end to bear upon the problem in question.

Problem 2. Second from the Right End

Following the series of control trials of problem 1 given to Skirrl on May 6, a period of four days was allowed during which the animal was merely fed in the boxes each day. This was done in order that he should partially lose the effects of his previous training to choose the first box at the left before being presented with the second problem, the second box from the right.

On May 11 regular experimentation was begun with problem 2. Naturally the situation presented unusual difficulties to the monkey because of his previously acquired habit, and on the first day it was possible to give only five trials, in all except the first of which Skirrl had to be aided by the experimenter to find the right box. He persistently, as appears in the first line of records of table 2, entered the first box at the left. The series was continued on May 13, but with very unsatisfactory results, since he apparently had been greatly discouraged by the unusual difficulties previously met. Only four trials could be given, and in these the showing made was very poor. It is noteworthy, however, that in trials 6, 7, and 8, May 13, there was no marked tendency to choose the first box at the left. Thus quickly had the force of the previous habit been broken.

For problem 2, the total number of open doors in the ten settings is fifty, as appears from the data on page 18, and as ten of these fifty open doors may be defined as right ones, the expected ratio of right to wrong first choices in the absence of previous training is 1 to 4. The actual ratio for the first series given in problem 2 is 1 to 8, while in the second series it is 0 to 10.

On the morning of May 13, work was interrupted in the ninth trial by what seemed at the moment a peculiarly unfortunate accident, but in the light of later developments, an incident most fruitful of valuable results.

Skirrl, in trial 9, directly entered box 1. Since this was not the right box, he was punished by being confined in it for ten seconds. While in the box he howled and when the entrance door was raised for him to retrace his steps, he came out with a rush, showing extreme excitement and either rage or fear, I could not be sure which. At intervals he uttered loud cries, which I am now able to identify as cries of alarm. Repeatedly he went to the open door of box 1 and peered in, or peered down through the hole in the floor which received the staple on the door. He refused to enter any one of the open boxes and continued, at intervals of every half minute or so, his cries. For thirty minutes I waited, hoping to be able to induce him to complete the series of trials, but in vain. Although it was obvious that he was eager to escape from the apparatus, he would not enter any of the boxes even when the exit doors were raised. Instead, he gnawed at the door (12 in fig. 17) to the alleyway D and attempted to force his way through, instead of taking the easy and clear route to the alleys, through one of the boxes. His behavior was most surprising and puzzling. Finally, I gave up the attempt to complete the series and returned him to his cage by way of the entrance door to the response-compartment E.

I then entered the apparatus to seek some explanation of the animal's behavior, and my search was rewarded by the finding of two sharp pointed nails which protruded for an inch or more in the middle of the floor of box 1. My assistant, who had been charged with the task of installing the locks for the several doors, had used nails instead of screws for attaching staples underneath the floor and had neglected to clinch the nails. Skirrl, in the dim light of the box, doubtless stepped upon one of the nails and inflicted a painful, although not serious, injury upon himself. It was impossible for him to see clearly the source of his injury. He was greatly frightened and expressed the emotion most vigorously. His behavior strongly suggested a superstitious dread of some unseen danger. It may be that the instinctive fear of snakes, so strong in monkeys, was partly responsible for his response.

The first result of this accident was that more than two weeks were lost, for it was impossible, during the next few days, to induce the animal to enter any of the multiple-choice boxes voluntarily. From May 14 to May 24, I labored daily to overcome his newly acquired fear. The usual procedure was to coax him through one box after another by standing at the exit door with some tempting morsel of food. After several days of this treatment, he again trusted himself to the boxes, although very circumspectly and only when both entrance and exit doors were raised. Not until May 24 was it possible to resume regular experimentation, and on that day it was found necessary to indicate the right box by raising the exit door slightly and then immediately lowering it. Trials in which this form of aid was given are indicated in table 2 by a star following the last choice.

Gradually, Skirrl regained his confidence in the apparatus and began to work more naturally. For a long time he would not stand punishment, and it was necessary for the experimenter to be very careful in locking the doors, since the sound of the bar sliding beneath the floor often frightened and caused him to quit work. Day after day the tendency to peer through the holes in the floor at the entrance to the boxes rendered it clear that the animal feared some danger from beneath the floor. This behavior was so persistent that much time was wasted in the experiments.

On the last day of May, punishment by confinement for ten seconds in wrong boxes was introduced, but since this tended to discourage the monkey, there was substituted for it on June 1 the punishment of forcing him to work his way out of each wrong box by raising the entrance door which had been closed behind him. This he could fairly readily do, and his stay in a box rarely measured more than ten seconds.

As a variation in the mode of procedure, confinement for thirty seconds was tried on June 5, but it worked unsatisfactorily and had to be abandoned. During this series, the animal was startled by the sound from one of the sliding bars under the floor, and in the sixth trial he refused to work.

As improvement was very slow, varied modes of rewarding and punishing the animal were tried in the hope of discovering a means of facilitating the work. Among the former are the use of banana, grapes, peanuts, and other eagerly sought foods in varying quantities, and in the latter are included periods of confinement ranging from ten seconds to sixty seconds. In the end, confinement of about thirty seconds, combined with a small quantity of food which was much to the monkey's taste, gave most favorable results.

All this time Skirrl's attention to the task in hand was seldom good. He was easily diverted and even when extremely hungry, often stopped work in the middle of an early trial, yawned repeatedly and finally sat down to wait for release from the apparatus.

The results obtained during the long continued trials with this animal in problem 2 are presented in table 2, which differs from the previously described table, first, in that several of the trials are followed by an asterisk to indicate that aid was given by the experimenter, and second, in that two additional columns, headed, respectively, R and W, are presented. These give the right and wrong first choices for each day, whereas the two columns preceding them give the same data for each series of ten trials. Similarly, the ratio of right to wrong choices is presented for each day in table 2, instead of for each series of ten trials as in table 1.

From the results of table 2, several peculiarly interesting facts appear. In the first place the influence of the habit of choosing the first box at the left disappears with surprising suddenness, and in the second place, there are remarkable contrasts in the results for different settings as they appear in their respective vertical columns. Thus, in the case of setting 1, after the first trial mistakes became relatively infrequent, whereas in setting 6, which involved the same number of doors, mistakes continued to be the rule until nearly a thousand trials had been given. The most likely explanation of this difference is that for some reason the animal avoided box 9.

The reactive tendencies, or better, the methods of reaction which manifested themselves during this long series of observations may be described as follows: (a) choice of the first box at the left; (b) random choice with tendency to choose first, a box near the middle of the group; (c) choice of first box at the right followed by the one next to it on the left; (d) direct choice of the right box.



TABLE 2

Results for Skirrl, P. irus, in Problem 2

========================================================================================================================================= No. S.1 S.2 S.3 S.4 S.5 S.6 S.7 S.8 S.9 S.10 Ratio Date of 1.2.3.4.5 R W R W of trials 7.8.9 1.2.3.4 2.3.4.5.6.7 1.2.3.4.5.6 4.5.6.7.8 1.2.3 2.3.4.5 6.7.8.9 1.2.3.4 3.4.5.6.7.8 R to W - - - - - May 11&13 1- 9 7.7.9.7.8 {1.2.2.1.4.1 {2.3.2.3.2.5 {4.6.1.4.1.1 4.4.7 3.1.2 4 4.1.8 1 1 8 1 8 1: 8.00 {2.1.2.1.3 {2.3.2.5.6 {2.6.1.6.5 24 11- 20 8*[1] 2.4.3* 4.5.6* 2.2.5* 5.6.6.7* 3.1.2 {5.2.3.5.3.2 4.6.8* 4.4.3* 5.5.6.7* 0 10 0 10 0:10.00 {3.5.2.4* 25 21- 30 8* 4.4.3* 5.6 {6.6.2.3.4 6.7 2 4 5.6.3.8 4.4.3 6.4.6.8.7 2 8 2 8 1: 4.00 {6.6.5* 26 31- 40 8 4.3 6 4.5 6.7 3.2 5.4 5.8 4.3 5.3.8.7 2 8 2 8 1: 4.00 27 41- 50 8 4.4.3 6 5 6.8.6.8.7 3.3.3.2 5.4 {6.5.4.3 4.3 5.4.8.7 3 7 3 7 1: 2.33 {2.1.5.8 28 51- 60 8 4.4.3 7.6 5 5.6.7 3.3.3.2 4 {5.4.3 4.3 {5.4.3.3.4.5 3 7 3 7 1: 2.33 {3.6.8 {6.4.3.5.7 29 61- 70 8 4.3 6 6.6.5 7 3.3.3.2 5.4 7.6.4.7.6.8 4.3 7 4 6 4 6 1: 1.50 31 71- 80 8 4.4.4.3 6 6.5 6.8.7 3.2 5.4 {6.7.6.4.3 4.3 6.7 2 8 2 8 1: 4.00 June {2.6.3.7.8 {6.8.6.5.4 1 81- 90 8 4.3 6 5 {6.5.6.5.8 3.1.3.2 5.4 8 4.3 7 5 5 {5.4.6.4.7 " 91- 100 9.7.8 4.2.4.3 7.5.6 5 6.8.7 3.3.1.2 5.3.4 8 4.3 6.8.7 2 8 7 13 1: 1.86 2 101- 110 8 4.3 6 5 7 3.2 5.4 7.8 4.3 6.8.6.5.7 4 6 " 111- 120 8 4.3 7.3.5.7.6 {6.2.3.6.4 7 3.2 {5.2.3.5.3.2 9.6.4.7.8 {4.1.2 6.8.7 2 8 6 14 1: 2.33 {3.6.2.5 {3.5.2.3.4 {4.2.3 {6.8.6.3 3 121- 130 8 4.4.3 6 5 6.7 3.2 {5.3.2.3 8 4.2.3 {5.4.5.8.8 4 6 {5.2.5.4 {6.3.8.7 " 131- 140 8 4.3 5.7.3.2.6 4.5 5.7 1.3.2 5.3.4 6.7.8 4.2.1.3 7 2 8 6 14 1: 2.33 4 141- 150 8 4.3 7.6 6.5 7 2 {5.3.2.3 6.8 4.1.3 5.6.7 3 7 {5.5.4 " 151- 160 8 4.3 6 5 6.7 2 4 5.6.7.8 4.3 5.6.8.7 5 5 8 12 1: 1.50 5 161- 170 8 4.3 7.6 6.5 6.8.7 3.2 5.3.2.3.5.4 8 4.3 6.7 2 8 " 171- 176 8 2.4.3 7.6 6.5* 8.7 3.2* 1 5 3 13 1: 4.33 7 177- 180 5.4 8 4.4.3 8.7 1 3 " 181- 190 8 4.3 7.6 6.5 7 3.2 5.3.2.5.4 8 4.3 7 4 6 5 9 1: 1.80 8 191- 200 8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.3 8.7 2 8 " 201- 210 8 4.3 6 6.4.6.5 8.7 3.2 5.4 8 4.3 7 4 6 6 14 1: 2.33 9 211- 220 8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.3 8.6.7 2 8 " 221- 230 9.8 4.3 7.6 6.5 6.7 3.2 5.4 7.6.8 4.3 7 1 9 3 17 1: 5.67 10 231- 240 8 4.3 7.6 6.5 6.7 3.2 5.4 {3.2.3.2.4.3 4.3 7 2 8 2 8 1: 4.00 {2.5.4.7.8 11 241- 250 8 4.3 7.6 6.6.5 8.7 3.2 5.4 8 4.3 8.7 2 8 2 8 1: 4.00 12 251- 260 8 4.3 6 6.5 6.7 3.3.2 5.4 {7.6.7.7 3 3.7* 3 7 3 7 1: 2.33 {6.9.8* 14 261- 270 8 3 6 6.5 7 3.2 5.4 {5.3.4.3 3 {3.3.3.3.4 5 5 5 5 1: 1.00 {9.8* {4.6.4.7* 15 271- 280 7.9.8 4.2.3 3.4.3.7.6 6.5 8.7 3.2 5.4 8 4.3 8.7 1 9 " 281- 290 8 4.3 7.6 6.5 7 3.2 5.4 7.8 4.3 7 3 7 4 16 1: 4.00 {4.3.2.3 16 291- 300 7.8 {4.4.4 6 6.5 7 3.3.2 5.4 {6.5.4.3 4.3 6.7 2 8 {4.4.3 {5.6.7.8 " 301- 310 8 4.4.3 7.6 6.5 7 3.3.2 5.5.4 {7.6.5.4.6 4.3 7 3 7 5 15 1: 3.00 {5.7.9.8 17 311- 320 7.8 4.3 7.6 6.6.5 7 3.2 5.4 7.6.7.6.7.8 4.3 7 2 8 " 321- 330 8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.3 6.7 2 8 4 16 1: 4.00 18 331- 340 7.7.8 4.3 6 6.5 7 3.2 5.4 8 4.3 7 4 6 " 341- 350 8 4.3 7.6 6.6.5 8.7 3.2 5.4 8 4.3 7 3 7 7 13 1: 1.86 19 351- 360 8 4.3 7.6 6.5 6.5.6.5.7 3.2 5.4 8 4.3 7 3 7 " 361- 370 8 4.3 7.6 6.4.3.6.5 7 3.2 5.4 9.8 4.3 7 3 7 6 14 1: 2.33 21 371- 380 8 4.3 7.6 6.5 7 3.2 5.4 7.8 4.3 8.7 2 8 " 381- 390 8 4.3 7.6 6.5 7 3.2 5.4 8 4.3 7 4 6 6 14 1: 2.33 22 391- 400 8 4.3 7.6 6.5 6.5.4.6.7 3.3.3.2 5.4 6.7.8 4.4.3 7 2 8 " 401- 410 8 3 7.6 6.5 8.7 2 5.4 6.7.7.8 3 7 5 5 7 13 1: 1.86 23 411- 420 8 4.4.3 7.6 6.5 8.7 3.2 5.4 {7.6.7.6 4.3 7 2 8 2 8 1: 4.00 {6.7.8 24 421- 430 8 4.3 6 6.5 7 3.2 5.4 8 3 7 6 4 " 431- 440 8 3 7.6 6.5 7 3.3.2 5.4 8 4.3 7 5 5 11 9 1: 0.82 25 441- 450 7.8 4.4.3 7.6 6.5 6.5.7 3.3.2 5.5.4 7.8 4.3 7 1 9 1 9 1: 9.00 26 451- 460 7.8 4.3 7.6 6.5 7 3.2 5.4 8 4.3 7 3 7 " 461- 470 8 4.3 7.6 6.5 7 3.2 5.4 8 4.3 8.7 3 7 6 14 1: 2.33 28 471- 480 8 4.4.3 7.6 6.5 7 3.2 5.4 9.8 3 8.7 3 7 3 7 1: 2.33 29 481- 490 8 4.3 7.7.6 6.5 7 3.2 5.4 8 4.3 8.7 3 7 3 7 1: 2.33 30 491- 500 7.9.8 4.3 7.6 6.5 7 3.2 5.4 8 4.3 7 3 7 " 501- 510 8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.4.3 8.7 2 8 5 15 1: 3.00 July 1 511- 520 8 4.3 7.6 6.5 7 3.2 5.4 8 4.3 7 4 6 4 6 1: 1.50 2 521- 530 8 4.3 7.6 6.5 7 3.2 5.4 {7.6.5.6.5 4.4.3 7 3 7 {6.5.6.8 " 531- 540 8 4.3 7.6 6.5 7 3.2 5.4 8 4.3 7 4 6 7 13 1: 1.86 3 541- 550 7.8 4.4.3 6 6.5 7 3.2 5.4 8 4.3 5.5.7 3 7 " 551- 560 7.8 4.3 6 6.5 7 3.2 5.4 8 3 7 5 5 8 12 1: 1.50 5 561- 570 7.7.8 4.3 6 6.5 6.7 3.3.2 5.4 8 4.3 7 3 7 " 571- 580 8 4.3 6 6.5 7 3.2 5.4 7.8 4.3 7 4 6 7 13 1: 1.86 {6.5.4.6.5 6 581- 590 7.8 4.3 7.6 6.6.5 {5.4.5.4.4 2 3.4 6.5.4.3.7.8 3 7 3 7 3 7 1: 2.33 {6.5.6.5.8.7 7 591- 600 8 4.3 6 6.5 7 3.2 5.4 7.8 4.3 8.7 3 7 " 601- 610 7.8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.3 8.7 1 9 4 16 1: 4.00 8 611- 620 8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.3 8.7 2 8 " 621- 630 8 4.3 7.6 6.5 8.7 3.2 5.4 9.8 4.3 8.7 1 9 " 631- 640 8 4.4.3 7.7.6 6.5 8.7 3.2 4 8 4.3 8.7 3 7 6 24 1: 4.00 9 641- 650 7.8 4.3 7.6 6.5 6.7 3.2 {3.2.5.3 7.6.5.4.8 3 8.7 1 9 1 9 1: 9.00 {2.5.4 {6.5.4.3.7 10 651- 660 7.8 4.3 6 6.5 7 3.2 5.4 {6.5.4.7.6 4.3 7 3 7 {5.4.8 10 661- 670 8 3 7.6 5 7 3.2 5.4 8 3 8.7 6 4 9 11 1: 1.22 12 671- 680 7.8 3 6 6.5 7 3.2 5.4 6.5.4.7.8 4.3 8.7 3 7 3 7 1: 2.33 13 681- 690 8 3 7.6 6.5 {6.5.4 3.2 4 6.7.8 3 {6.5.4.5 4 6 {6.5.7 {6.5.8.7 " 691- 700 8 3 6 5 7 3.2 5.4 8 3 7 8 2 12 8 1: 0.67 14 701- 710 8 3 7.6 6.5 {6.5.4.5 2 3.5.4 8 3 7 6 4 {4.6.8.7 " 711- 720 8 3 6 5 7 2 5.4 6.5.4.8 3 6.5.7 7 3 13 7 1: 0.54 15 721- 730 7.8 3 6 6.5 7 3.2 5.4 8 4.3 7 5 5 " 731- 740 8 3 7.6 6.5 7 3.2 5.4 8 3 7 6 4 11 9 1: 0.82 16 741- 750 7.8 3 6 6.5 7 3.2 4 8 3 7 7 3 " 751- 760 7.8 3 7.6 6.5 7 2 4 7.8 4.3 7 5 5 12 8 1: 0.67 17 761- 770 8 4.3 6 5 8.7 3.2 5.4 8 4 7 6 4 " 771- 780 8 2.2.3 7.6 6.5 7 3.2 5.4 7.8 4.3 7 3 7 9 11 1: 1.22 19 781- 790 8 3 7.6 5 7 3.2 3.4 7.6.5.8 3 7 6 4 " 791- 800 7.8 3 6 5 7 2 5.4 8 3 6.5.6.7 7 3 " 801- 810 8 2.3 6 5 6.5.7 2 5.4 8 3 7 7 3 20 10 1: 0.50 20 811- 820 7.8 3 7.6 5 7 3.3.2 5.4 8 2.2.3 7 5 5 " 821- 830 8 3 6 6.5 7 3.2 4 8 2.3 8.7 6 4 11 9 1: 0.82 21 831- 840 8 3 5.4.5.6 5 7 2 4 6.7.8 3 8.7 7 3 " 841- 850 8 3 7.6 5 7 3.2 3.2.4 8 3 7 7 3 14 6 1: 0.43 22 851- 860 8 4.3 6 5 7 3.2 3.5.4 8 3 8.7 6 4 " 861- 870 7.8 4.3 7.6 6.5 8.7 3.2 4 8 3 8.7 3 7 " 871- 880 8 4.3 7.6 6.5 8.7 3.2 5.4 8 4.3 8.7 2 8 11 19 1: 1.73 23 881- 890 8 3 7.6 6.5 8.7 3.2 5.4 8 3 8.7 4 6 " 891- 900 8 3 7.6 6.5 7 3.3.2 5.4 8 4.3 7 5 5 9 11 1: 1.22 24 901- 910 8 4.3 7.6 6.5 7 3.2 5.4 8 3 8.7 4 6 " 911- 920 8 3 7.6 5 7 3.2 5.4 8 3 7 7 3 11 9 1: 0.82 26 921- 930 7.8 3 7.6 5 7 3.2 5.4 8 2.2.3 8.7 4 6 " 931- 940 8 3 7.6 6.5 8.7 3.2 5.5.4 8 4.3 8.7 3 7 7 13 1: 1.86 27 941- 950 8 3 6 6.5 7 3.2 5.4 8 3 7 7 3 7 3 1: 0.43 28 951- 960 8 3 7.6 6.5 5.4.7 2 5.5.4 8 3 7 6 4 6 4 1: 0.67 29 961- 970 8 3 7.6 5 8.7 2 4 8 3 7 8 2 8 2 1: 0.25 30 971- 980 8 3 4.3.2.6 5 {6.5.4.6 2 5.5.4 8 3 7 7 3 7 3 1: 0.43 {6.5.7 31 981- 990 8 3 6 6.5 8.7 2 4 8 3 7 8 2 8 2 1: 0.25 August 2 991-1000 8 3 7.6 5 7 2 {2.3.5.3 7.6.8 3 7 7 3 7 3 1: 0.43 {2.3.3.4 3 1001-1010 8 3 7.6 5 7 2 4 7.6.5.6.7.8 3 5.4.3.4.3.7 7 3 " 1011-1020 8 2.3 5.6 3.2.3.6.5 7 2 5.4 9.8 2.1.3 7 4 6 11 9 1: 0.82 4 1021-1030 7.8 3 5.4.3.7.6 6.5 {6.5.6 3.2 5.4 8 {2.2.4.2 8.7 2 8 {5.6.7 {4.2.3 " 1031-1040 7.8 3 6 6.4.3.6.5 7 2 3.5.4 8 2.3 8.7 5 5 7 13 1: 1.86 5 1041-1050 8 3 6 2.3.2.6.5 8.7 2 4 8 2.2.4.3 {8.8.6.8.4 6 4 6 4 1: 0.67 {6.5.8.7 6 1051-1060 8 3 6 4.2.6.5 7 3.2 5.4 8 3 8.7 6 4 6 4 1: 0.67 7 1061-1070 8 3 5.4.3.6 4.5 {6.5.6.5 2 4 8 3 7 7 3 7 3 1: 0.43 {4.8.7 9 1071-1080 8 3 6 5 7 2 4 8 3 7 10 0 10 0 1: 0.00 - - - - - 1.2.3.4.5 1.2.3.4 2.3.4.5 5.6.7.8 2.3.4.5.6 6.7.8.9 5.6.7 1.2.3.4 4.5.6 2.3.4.5 1.2.3 5.6.7 6.7.8.9 - - - - - 10 1- 10 6.5.7 3.2.6.5 8 6 2.4.3 5 5.4 2 7.5.2.7.6 8 5 5 5 5 1: 1.00 11 11- 20 7 3.6.5 8 6 3 6.5 4 3.2 7.6 8 6 4 6 4 1: 0.67 {3.2.3.5.3 12 21- 30 7 2.2.6.5 7.8 6 3 5 {2.5.3.2 2 6 8 7 3 7 3 1: 0.43 {5.3.2.5 {2.5.5.4 =====================================================================================================================================================

[Footnote 1: First choices correct by reason of aid from the experimenter are not counted as correct (R) in the summary.]

[Footnote *: Aided by experimenter.]

The method of choosing the first box at the right end and then the one next to it developed in the case of all except two of the ten settings. The time of appearance is worth noting. In setting 1, it failed to appear; in setting 2, it developed early,—after about one hundred trials; in setting 3, after about one hundred and fifty trials; in setting 4, after about one hundred and fifty trials; in setting 5, after about one hundred and seventy trials; in setting 6, after about one hundred trials; in setting 7, after about fifty trials; in setting 8, it never developed; in setting 9, after about fifty trials; and in setting 10, it developed very late,—after about four hundred and seventy trials.

This method of reaction, although inadequate, proved remarkably persistent, and it is doubtful whether it had been wholly overcome at the conclusion of the experiment. In the case of the series of trials given on June 8, numbered 191 to 200, the method used was either that of the first at the right and then the next, or direct choice of the right box.

Throughout the trials with this problem, the end boxes, numbers 1 and 9, were avoided. This is at least partially explained by the fact that they never existed, and obviously never could appear, in problem 2, as right boxes. In trials 601 to 610, given on July 7, there occurred partial return to the formerly established method of choosing the first door at the right. This relapse was characteristic of what happened during the many days which intervened between the definite appearance of this habit and the final solution of the problem.

Especially in connection with such relapses, Skirrl showed extreme fatigue or ennui and often would refuse to work and simply sit before the open doors yawning. This happened even when he was extremely hungry and evidently eager enough for food.

From July 12 on the hunger motive was increased by feeding the monkey only in the apparatus and by so regulating the amount of food given in each trial that he should obtain barely enough to keep him in good physical condition. An increase in the number of correct choices promptly resulted, and continued until on July 14 the ratio of choices was 1 to .54. It appeared from these data that a relatively small number of choices, say not more than ten a day, the rewards in connection with which supplied the only food received by the animal, yielded most favorable results.

On July 16, the period of confinement in wrong boxes was increased to sixty seconds, and it was so continued for a number of days. But in the end, it became clear that the period of thirty seconds, combined with a liberal reward in the shape of desired food and a single series of ten trials per day, was most satisfactory. The detailed data of table 2 indicate that at this time Skirrl was making his choices by memory of the particular setting.

Skirrl, on July 17 was evidently hungry and eager to locate food, but seemingly unable to select the right box. In trial 5 (765th) of the series, he was punished by confinement in box 8. When the doors were unlocked in order that the entrance door might be raised to release him, the lock-bar, sliding under the floor, made a slight grating noise, and the instant the entrance door was opened, he jumped out excitedly. He made no outcry, but as soon as he was out of the box, sat down, and taking up his right hind foot, examined it for a few seconds. Having apparently assured himself that nothing serious had happened, he went on unconcernedly about his task. The presumption is that the sound of the lock-bar, associated as it was with his painful experience in box 1, revived the strongly affective experience of stepping on the nail. Psychologically described, the sound induced an imaginal complex equivalent to the earlier painful experience. The behavior seems to the writer a most important bit of evidence of imagery in the monkey. Finally, on August 9, after ten hundred and seventy trials, Skirrl succeeded in choosing correctly in the ten trials of a series, and he was therefore considered to have solved the problem of the second door from the right end of the group.

On the following day, he was given a control series with the settings which are presented on page 19 and also at the bottom of table 2. In this series he chose correctly five times,—in other words, as often correctly as incorrectly. An analysis of the choices indicates, however, that two of the five correct choices were made in box 8, which, as it happened, had proved a peculiarly easy one for him throughout the training, since from the first he tended to avoid door 9. Consequently, it is only fair to conclude, from the results for this control series and for those given on August 11 and 12, that the animal chose not on the basis of anything remotely resembling a general idea of secondness from the right end, but instead on the basis of gradually acquired modes of reaction to the particular settings. This conclusion is strengthened by the fact that he had failed to learn to react appropriately and readily to most of the settings of the regular series.

The curve which represents the course of the learning process in this problem is presented in figure 19. For this and all other curves which involve more than a single series of observations a day, the method of construction was as follows: The first series for each day of training is indicated on the curve by a dot, while the second or third series on a given day, although space is allowed for them, are not so indicated. Consequently, the form of the curve is determined chiefly by the first series per day. The extreme irregularities of this curve are most interesting and puzzling, as are also the variations in the daily ratios of right to wrong first choices. Three times in the course of the training, this ratio rose to 1 to 9, or higher. The causes for such extreme variations are not easily enumerated, but a few of the most obvious contributory causes are variations in the weather, especially cloudiness or fogginess, which rendered the apparatus dark; variations in the degree of hunger or eagerness for food; differences in the activities of the animals in the cages outside of the laboratory (sometimes they were noisy and distracted the subject), and finally, differences in the physical fitness and attitude of the animal from day to day.

The more or less incidental behavior in connection with this experiment more strongly than the statistical results of the work on problem 2 indicate the existence of imagery. That ideas played a part in the solution of the problem is probable, but at best they functioned very ineffectively. The small number of methods used in the selection of the right box, and the slight variations from the chief method, that of choosing the first box at the right end and then the one next to it, apparently justify Doctor Hamilton's characterization of this monkey as defective.



Problem 3. Alternately First at Left and First at Right

Following the control series given in connection with problem 1, an interval of rest lasting from August 12 to August 19 was allowed in order that Skirrl might in part at least lose the effects of his training and regain his customary interest in the apparatus by being allowed to obtain food easily instead of by dint of hard labor,—labor which was harder by far, apparently, than physical activity because it demanded of the animal certain mental processes which were either lacking or but imperfectly functional. The difficultness of the daily tasks appears to be reliably indicated by the tendency to yawn.

Systematic work on problem 3, which has been defined as alternately the first door at the left and the first door at the right of the group, was begun August 19, and for nine days a single series of ten trials per day was given. Work then had to cease because of the experimenter's return to Cambridge.

The results of the work on this problem demand but brief analysis and comment. The expected ratio of one right to four wrong choices per series appears (see table 3) for the first series of trials, and this in spite of the fact that Skirrl had been trained for several weeks to choose the second door from the right end. One would ordinarily have predicted a much larger number of incorrect choices. The right choices were due to the monkey's strong tendency to go first to the first door at the right and thence to the one next to it. Indeed in the series given on August 24; this method was followed without variation. In other words, in every one of the ten trials Skirrl entered first the box at the extreme right end of the group. This necessarily resulted in as many right as wrong first choices. Consequently, the ratio reads 1 to 1. But the method was not adhered to, and at no time either before or after that date did he succeed in equalling this achievement. There was, as a matter of fact, no steady improvement, and so far as one may judge from the records which were obtained, the course of events in the solution of this problem would have been similar to those in problem 2.



TABLE 3

Results for Skirrl, P. irus, in Problem 3

========================================================================================================================================= Date No. of S.1 S.2 S.3 S.4 S.5 S.6 S.7 S.8 S.9 S.10 R W R W Ratio of trials 5.6.7 5.6.7 1.2.3.4.5.6 1.2.3.4.5.6 4.5.6.7.8 4.5.6.7.8 2.3.4.5 2.3.4.5 3.4.5.6.7.8.9 3.4.5.6.7.8.9 R to W __ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ _ _ _ _ __ August {6.5.4.6 {8.7.6.5 19 1- 10 7.5 6.7 {3.2.6.4 5.3.6 {7.8.7.6 8 4.3.5.4.5.2 5 9.8.7.6.4.3 {4.5.8.7 2 8 2 8 1:4.00 {3.6.1* {8.6.4 {6.5.9* {5.4.6.5 {8.7.6.7 20 11- 20 7.6.5 {6.5.6.5 {4.6.5.3 5.3.2.4.6 {7.5.8.8 8 5.4.3.2 4.5 8.7.6.5.4.3 {8.7.6.8.3 1 9 1 9 1:9.00 {7 {2.5.1* {7.6.4* {7.6.4.3.9 {6.2.5.6 {5.3.5.4 21 21- 30 7.6.7.6.5 7 {5.3.6.5 2.5.5.6 8.6.5.4 8 {3.5.3.5 5 {9.8.7.6 8.9 3 7 3 7 1:2.33 {4.3.1* {4.3.2* {5.4.3 23 31- 40 7.6.5 6.5.7 {6.4.3.2 3.2.6 8.7.6.4 8 5.4.5.3.2 5.2 8.7.3 9 2 8 2 8 1:4.00 {5.6.2.1 24 41- 50 7.6.5 7 {6.2.5 6 {8.7.8.7 8 5.3.2 5 {9.8.7.6 9 5 5 5 5 1:1.00 {4.3.1 {5.7.5.4 {5.4.3 {8.7.3.6 25 51- 60 7.6.5 6.5.7 5.2.1 6 8.5.4 8 2 2.5 9.8.7.4.3 {8.7.5.3 3 7 3 7 1:2.33 {8.7.9* 26 61- 70 7.6.5 6.5.7 1 2.1.6 8.7.6.4 8 2 3.2.5 9.8.7.5.3 {3.6.8.3 3 7 3 7 1:2.33 {4.7.9 {8.6.3.3 27 71- 80 7.6.5 7 2.1 1.5.6 8.7.6.4 8 2 5 9.8.7.6.3 {7.5.3.8 4 6 4 6 1:1.50 {3.6.9* 28 81- 90 7.6.7.5 7 3.1 6 8.6.4 4.8 2 2.4.5 8.7.4.3 3.8.9 3 7 3 7 1:2.33 =====================================================================================================================================================

[Footnote *: Aided by experimenter.]



2. Sobke, Pithecus rhesus

Problem 1. First at the Left End

Sobke was somewhat afraid of the experimenter when the investigation was undertaken, and instead of willingly coming out of his cage when the door was raised, he often had to be coaxed out and lured into the apparatus with food. Whereas Skirrl was frank and rather aggressive, Sobke was stealthy in his movements, furtive, and evidently suspicious of the experimenter as well as of the apparatus. He was perfectly safe to approach, but would not permit anyone to touch him. After a few days, he began to take food from the hands of the experimenter.

Preliminary work to acquaint this monkey with the routine of the experiment was begun on April 13. As in the case of Skirrl, he was lured into the apparatus and was taught the route through the boxes to the starting point by being allowed to obtain food once each day in each of the nine boxes. The procedure was simple. The entrance door and the exit door of a particular box were raised and the animal admitted to the reaction-compartment and permitted to pass through the box whose doors stood open, take its food, and return to the starting point. Sobke very quickly learned the route perfectly and came to work steadily and rapidly. After five days of preliminary work of this sort, he was so thoroughly accustomed to the apparatus that it was evidently desirable to begin with regular training experiments.

The first series of trials was given on April 19. Both punishment and reward were employed from the first. The punishment consisted of confinement for thirty seconds in each wrong box, and the reward of a small piece of banana, usually not more than a tenth of a medium sized banana for each correct choice. The total time for the first series of trials was fourteen minutes. This indicates that Sobke worked rapidly. My notes record that he worked quickly though shyly, wasted almost no time, made few errors of choice, and waited quietly during confinement in the boxes. In this, also, he differed radically from Skirrl who was restless and always tried to escape from confinement.

Throughout the work on problem 1, punishment and reward were kept constant. Everything progressed smoothly; there were no such irregularities of behavior as appeared in the case of Skirrl, and consequently the description of results is a relatively simple matter. Sobke invariably chose the end boxes. His performance was in every way superior to that of Skirrl.

As previously, the detailed results are presented in tabular form (table 4). From this table it appears that, whereas the expected ratio of right to wrong first choices for this problem is 1 to 2.5, the actual ratio for Sobke's first series was 1 to .67. This surprisingly good showing is unquestionably due to his marked tendency to choose the end box of a group; and this tendency, in turn, may in part be the result of the preliminary training, for during that only one box was open each time. But, if the preliminary training were responsible for Sobke's tendency, it should be noted that it had very different effect upon Skirrl, and, as will be seen later, upon Julius.

The results for the ten different settings of the doors for problem 1 as they appear in table 4 are of interest for a number of reasons. In the first place, the setting 1. 2. 3 appearing twice,—at the beginning of the series and again at the end—yielded markedly different results in the two positions. For whereas no mistakes were made in the case of setting 1, there were fifty per cent of incorrect first choices for setting 10. Again, satisfactory explanation is impossible. It is conceivable that fatigue or approaching satiety may have had something to do with the failures at the end of the series, but as a rule, as is indicated by settings 1, 2, and 6, if correct choices were made at the beginning, they continued throughout the day's work.

In this problem, Sobke's improvement was steady and fairly rapid, and in the eighth series, trials 71 to 80, only correct first choices appear. Consequently, seventy trials were required for the solution of the problem. This number is in marked contrast with Skirrl's one hundred and thirty-two trials.

Immediately following the first perfect series, Sobke was given two series of control tests on April 28. Conditions were unfavorable, since the day was stormy and the rain pattering on the sheet-iron roof made a great din. Nevertheless, he worked steadily and well up to the sixth trial, which was preceded by a slight delay because of the necessity of refilling some of the food boxes. After this interruption, wrong choices occurred in trial 6. And again after trial 9, there was brief interruption, followed by wrong choices in trial 10. The ratio of right to wrong choices for this first control series was therefore 1 to .25.



TABLE 4

Results for Sobke, P. rhesus, in Problem 1

========+==========+============+==========+==========+==========+==========+==========+==========+==========+==========+============+==+==+==+==+======= No. S.1 S.2 S.3 S.4 S.5 S.6 S.7 S.8 S.9 S.10 Ratio Date of R W R W of trials 1.2.3 8.9 3.4.5.6.7 7.8.9 2.3.4.5.6 6.7.8 5.6.7 4.5.6.7.8 7.8.9 1.2.3 R to W + -+ + + + + + + + + + + -+ -+ -+ -+ April 19 1-10 1 8 3 9.7 6.2 6 7.5 4 9.7 1 6 4 6 4 1:0.67 20 11-20 1 8 3 7 2 6 7.5 8.4 9.9.7 1 7 3 7 3 1:0.43 21 21-30 1 8 4.3 9.7 2 6 5 8.4 7 1 7 3 7 3 1:0.43 22 31-40 1 8 3 7 6.2 6 6.5 4 7 3.1 7 3 7 3 1:0.43 23 41-50 1 8 3 7 2 6 5 4 9.7 3.1 8 2 8 2 1:0.25 24 51-60 1 8 3 9.7 2 6 5 4 7 2.1 8 2 8 2 1:0.25 26 61-70 1 8 3 7 2 6 5 4 7 3.1 9 1 9 1 1:0.11 27 71-80 1 8 3 7 2 6 5 4 7 1 10 0 10 0 1:0.00 + -+ + + + + + + + + + + -+ -+ -+ -+ 2.3.4 1.2.3.4.5 2.3.4 6.7.8.9 3.4.5 4.5.6.7.8.9 6.7.8.9 1.2.3.4.5 5.6.7.8 3.4.5.6.7.8 5.6.7 6.7.8.9 + + + + + + + + + + + 28 1-10 2 6 3 4 6 5.4.1 2 3 5 5.4.2.1 8 2 " 11-20 2 6 3 4 6 2.1 2 3 5 1 9 1 17 3 1:0.18 =====+========+============+============+============+============+============+============+============+============+============+============+==+==+==+==+========

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