Another contribution that provides evidence of cognition in learning is the fascinating study reported by Kohler (1951) in his book entitled, Mentality of Apes. The study was conducted by Kohler off the coast of Africa at the anthropoid station maintained by the Prussian Academy of Science in Tenerife during the years 1913 to 1917. The majority of observations were made in the first six months of 1914 (p. 7). Kohler’s report on these experiments was published in 1917 in Intelligenzenprüfungen an Anthropoiden. The English version, The Mentality of Apes, was published in 1925.

Anthropoids were selected as the subjects of Kohler’s experiments both because of their similarity to man in intelligence and behavior, but simultaneously—and more importantly—because of their subordinate state of intelligence, which makes it possible to observe in the act of learning that which is not possible when observing the human adult:

Even assuming that the anthropoid ape behaves intelligently in the sense in which the word is applied to man, there is yet from the very start no doubt that he remains in this respect far behind man, becoming perplexed and making mistakes in relatively simple situations; but it is precisely for this reason that we may, under the simplest conditions, gain knowledge of the nature of intelligent acts. The human adult seldom performs for the first time in his life tasks involving intelligence of so simple a nature that they can be easily investigated; and when in more complicated tasks adult men really find a solution, they can only with difficulty observe their own procedure. (Kohler, 1951, pp. 1-2)

Kohler operationally defined intelligence as the utilization of roundabout methods—“detours, roundabout ways, paths or routes, circuitous routes and indirect ways” (p. 11)—to overcome obstacles:

As experience shows, we do not speak of behaviour as being intelligent, when human beings or animals attain their objective by a direct unquestionable route which clearly arises naturally out of their organization. But we tend to speak of “intelligence” when, circumstances having blocked the obvious course, the human being or animal takes a roundabout path, so meeting the situation. (Kohler, 1951, pp. 3-4)

All of his experiments were set up in this way, the direct path to the objective—usually a banana—being blocked, but a roundabout way being left open. Kohler was careful to set his experiments so as to require something beyond the roundabout way a chimpanzee might take in its normal behavior:

No one expects a chimpanzee to remain helpless before a horizontal opening in a wall, on the other side of which his objective lies, and so it makes no impression at all on us when he makes as horizontal a shape as he can of himself, and thus slips through. It is only when roundabout methods are tried on the lower animals, and when you see even chimpanzees undecided, nay, perplexed to the point of helplessness, by a seemingly minor modification of the problem—it is only then you realize that circuitous methods cannot in general be considered usual and matter-of-course conduct. (Kohler, 1951, p. 13)

He also set the experiments in such a way as to be able to distinguish between chance behavior that brings the subject in contact with the objective, and genuine achievement:

As chance can bring the animals into more favourable spots, it will also occasionally happen that a series of pure coincidences will lead them from their starting-point right up to the objective, or at least to points from which a straight path leads to the objective. This holds in all intelligence tests (at least in principle: for the more complex the problem to be solved, the less likelihood is there that it will be solved wholly by chance); and, therefore, we have not only to answer the question whether an animal in an experiment will find the roundabout way (in the wider meaning of the word) at all, we have to add the limiting condition, that results of chance shall be excluded. (Kohler, 1951, p. 16)

 

The genuine achievement takes place as a single continuous occurrence, a unity, as it were, in space as well as in time; in our example as one continuous run, without a second’s stop, right up to the objective. A successful chance solution consists of an agglomeration of separate movements, which start, finish, start again, remain independent of one another in direction and speed, and only in a geometrical summation start at the starting-point, and finish at the objective. The experiments on hens illustrate the contrast in a particularly striking way, when the animal, under pressure of the desire to reach the objective, first flies about uncertainly (in zigzag movements which are shown in Fig. 4a but in not nearly great enough confusion), and then, if one of these zigzags leads to a favourable place, suddenly rushes along the curve in one single unbroken run. (Kohler, 1951, pp. 16-17)

To separate problem solving behavior from normal or chance behavior, Kohler designed series of experiments that required the use of implements such as strings, sticks and boxes in order to obtain the objective. In these experiments, the banana could not be reached by making a detour, or by the body of the animal being adapted to the shape of its surroundings, but instead required the chimpanzee to make use of available objects as intermediaries. For example, in one series of experiments food was placed outside of the animal’s reach, but a string was fastened to it, the end of which was placed within reach. In this simple case, none of the animals ever hesitated to pull the string to draw the food to them (Kohler, 1951, p. 26). In a more complicated variation, multiple strings were used, sometimes crossing each other, with only one of the strings attached. In these experiments no conclusion could be drawn as to whether or not the chimpanzee actually recognized the “right” string or not. Consistently the animal would take a position behind the bars of the cage as close as possible to the objective, and begin pulling in rapid succession, starting with the closest string, until the food was obtained. In another variation, where only one string was used, but was not attached to the food, only placed in a position closer or farther from it, it was found that the animal would always pull the string if it visibly touched the objective. If the distance between the objective and the end of the string was wide, the chimpanzee would generally not pull the string, unless he was interested in the string itself, or wanted to use it in some other way (p. 30).

In yet another series of experiments, the objective was not connected in any way with the animals’ room but was only obtainable by means of pulling it in with a stick. Kohler’s description of one of his subjects, Tschego, is representative of the pattern he observed with other chimpanzees:

Tschego first tries to reach the fruit with her hand; of course, in vain. She then moves back and lies down; then she makes another attempt, only to give it up again. This goes on for more than half-an-hour. Finally she lies down for good, and takes no further interest in the objective. The sticks might be non-existent as far as she is concerned, although they can hardly escape her attention as they are in her immediate neighbourhood. But now the younger animals, who are disporting themselves outside in the stockade, begin to take notice, and approach the objective gradually. Suddenly Tschego leaps to her feet, seizes a stick, and quite adroitly, pulls the bananas till they are within reach. In this maneuver, she immediately places the stick on the farther side of the bananas. She uses first the left arm, then the right, and frequently changes from one to the other. She does not always hold the stick as a human being would, but sometimes clutches it as she does her food, between the third and fourth fingers, while the thumb is pressed against it, from the other side. (Kohler, 1951, pp. 31-32)

Another of Kohler’s examples clearly demonstrated how knowledge of the lay of the land known beforehand might be used to plan an indirect circuit through it:[1]

One room of the monkey-house has a very high window, with wooden shutters, that looks out on the playground. The playground is reached from the room by a door, which leads into the corridor, a short part of this corridor, and a door opening on to the playground. All the parts mentioned are well known to the chimpanzees, but animals in that room can see only the interior. I take Sultan with me from another room of the monkey-house, where he was playing with the others, lead him across the corridor into that room, lean the door to behind us, go with him to the window, open the wooden shutter a little, throw a banana out, so that Sultan can see it disappear through the window, but, on account of its height, does not see it fall, and then quickly close the shutter again (Sultan can only have seen a little of the wire-roof outside). When I turn round Sultan is already on the way, pushes the door open, vanishes down the corridor, and is then to be heard at the second door, and immediately after in front of the window. I find him outside, eagerly starching underneath the window; the banana has happened to fall into the dark crack between two boxes. Thus not to be able to see the place where the objective is, and the greater part of the possible indirect way to it, does not seem to hinder a solution; if the lay of the land be known beforehand, the indirect circuit through it can be apprehended with ease. (Kohler, 1951, pp. 20-21)

Kohler also found that an increase in motivation could be used to help the tiring chimpanzee persist and succeed:

The improvement of the objective by the addition of further items is a method which can be employed over and over again with success when the animal is obviously quite near to a solution, but, in the case of a lengthy experiment, there is the risk that fatigue will intervene and spoil the result. (pp. 42-43)

Some of the most well-known experiments in the study were those involving boxes, which the animals must use in order to obtain access to an objective fastened high above the ground and unobtainable by any circuitous routes. In setting up these experiments Kohler noted that “the possibility of utilizing old methods generally inhibits the development of new ones” (p. 39) and directed that all sticks should be removed before experiments with boxes were conducted. One such experiment is described as follows:

The six young animals of the station colony were enclosed in a room with perfectly smooth walls, whose roof—about two metres in height—they could not reach. A wooden box (dimensions fifty centimetres by forty by thirty), open on one side, was standing about in the middle of the room, the one open side vertical, and in plain sight. The objective was nailed to the roof in a corner, about two and a half metres distant from the box. All six apes vainly endeavored to reach the fruit by leaping up from the ground. Sultan soon relinquished this attempt, paced restlessly up and down, suddenly stood still in front of the box, seized it, tipped it hastily straight towards the objective, but began to climb upon it at a (horizontal) distance of half a metre, and springing upwards with all his force, tore down the banana. About five minutes had elapsed since the fastening of the fruit; from the momentary pause before the box to the first bite into the banana, only a few seconds elapsed, a perfectly continuous action after the first hesitation. Up to that instant none of the animals had taken any notice of the box; they were all far too intent on the objective; none of the other five took any part in carrying the box; Sultan performed this feat single-handed in a few seconds. (pp. 39-40)

Not all of the apes employed the boxes so quickly. For example, Koko took several weeks to learn to use the box (Kohler, 1951, pp. 39-45). However, once he figured it out, and successfully obtained the banana several times using the box as a platform, he would “turn towards the box and seize it as soon as anyone came in sight carrying edibles” (p. 45).

Kohler’s (1951) experiments also included situations in which the objective was obtained through use of a ladder or box brought in by the ape from outside the room in which the objective had been hung (p. 51); situations in which the apes positioned and climbed swinging doors to reach the objective (pp. 53-57); and even situations in which the apes used other apes, their keeper, or the observer as a means to reach the objective (p. 48). There were also experiments in which the apes could only reach the fruit by moving a large box (pp. 59-66), or by detouring from their purpose to obtain a stick, a piece of wire, a stone, or a rope that can be used as a tool (pp. 101- 119). In some situations the apes had to remove stones from boxes to make them light enough to move (pp. 119-120) or connect two short sticks together to make one stick long enough to reach the banana (p. 125). Problems were also set in which the apes must stack multiple boxes on top of each other (pp. 135-154), and combine this with the use of a reaching stick in order to get the fruit.

The purpose behind all of Kohler’s experiments was to determine whether or not apes “behave with intelligence and insight” and “to ascertain the degree of relationship between anthropoid apes and man” (1951, p. 1). His conclusion was that chimpanzees do, in fact, “manifest intelligent behavior of the general kind familiar in human beings,” so long as the experimental test are carefully designed to include only those limits of difficulty and functions within which “the chimpanzee can possiblyshow insight” and cautioned that “in general, the experimenter should recognize that every intelligence test is a test, not only of the creature examined, but also of the experimenter himself” (p. 265).

[1] cf. Tolman’s notion of cognitive maps. Note also that Kohler’s experiments were published prior to Tolman’s and that Tolman, as evident by his many references to Kohler in Purposive Behavior in Animals and Men (1932), was well aware of Kohler’s experiments.

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