"In The Mentality of Apes Kohler reports his classic experiments with chimpanzees in Teneriffe, which became one of the foundations of Gestalt psychology. The following account is typical for the discovery of the use of implements by apes:

'Nueva, a young chimpanzee bitch, was treated three days after her arrival. She had not yet made the acquaintance of the other animals but remained isolated in a cage. A little stick is introduced into her cage; she scrapes the ground with it, pushes the banana skins together in a heap, and then carelessly drops the stick at a distance of about three-quarters of a metre from the bars. Ten minutes later, fruit is placed outside the cage beyond her reach. She grasps at it, vainly of course, and then begins the characteristic complaint of the chimpanzee: she thrusts both lips -- especially the lower -- forward, for a couple of inches, gazes imploringly at the observer, utters whimpering sounds, and finally flings herself on to the ground on her back -- a gesture most eloquent of despair, which may be observed on other occasions as well. Thus, between lamentations and entreaties, some time passes, until -- about seven minutes after the fruit has been exhibited to her -- she suddenly casts a look at the stick, ceases her moaning, seizes the stick, stretches it out of the cage, and succeeds, though somewhat clumsily, in drawing the bananas within arm's length. Moreover, Nueva at once puts the end of her stick behind and beyond her objective. The test is repeated after an hour's interval; on this second occasion, the animal has recourse to the stick much sooner, and uses it with more skill; and at a third repetition, the stick is used immediately, as on all subsequent occasions.'

It is obvious that Nueva's accomplishment was not obtained by the trial-and-error method, nor by conditioned reflex. For her behavior, from the moment her eyes fell on the stick, was unwaveringly purposeful; she did not stumble on the solution by poking about aimlessly with the stick beyond the bars, but seized the stick, carried it to the bars, stretched it out of the cage, and placed it behind the banana. This smooth, deliberate sequence of action is something quite different from the behavior of Thorndike's cats in the puzzle box or of rats in a maze....

...The eureka process does not consist in inventing something new out of nothing, but in a bringing together of the hitherto unconnected. Nothing is created that was not already there, in the outside world and its mental reflection. Likewise, the so-called 'revolutions' in thought consist not in destruction, but in synthesis: In connecting the hitherto unconnected."

Wolfgang Kohler's Experiment with Sultan

source: Arthur Koestler, The Act of Creation, New York, 1949, p. 104

    "Nueva's discovery was the use of tools; the next one to be described is the making of tools. Its hero is Sultan, a genius among Kohler's chimpanzees:

    'Beyond some bars, out of arm's reach, lies an objective [a banana]; on this side, in the background of the experiment room, is placed a sawn-off caster-oil bush, whose branches can be easily broken off. It is impossible to squeeze the three through the railings, on accont of its awkward shape; besides, only one of the bigger apes could drag it as far as the bars. Sultain is let in, does not immediately see the objective, and, looking about him indifferently, sucks one of the branches of the tree. But, his attention having been drawn to the objective, he approaches the bars, glances outside, the next moment turns around, goes straight to the tree, seizes a thin slender branch, breaks it off with a sharp jerk, runs back to the bars, and attains the objective. From the turning round upon the tree up to the grasping of the fruit with the broken-off branch, is one single quick chain of action, without the least 'hiatus', and without the slightest movement that does not, objectively considered, fit into the solution described.'

    "Had Sultan known Greek he would certainly have shouted Eureka!...

    "The act of discovery has a disruptive and a constructive aspect. it must disrupt rigid patterns of mental organization to achieve the new synthesis. Sultan's habitual way of looking at the tree as a coherent, visual whole had to be shattered. Once he had discovered that branches can be made into tools he never again forgot it, and we may assume that a tree never again looked the same to him as before. He had lost the innocence of his vision, but from this loss he derived an immense gain: the perception of 'branches' and the manipulation of 'tools' were now combined into a single, sensory-motor skill; and when two matrices have become integrated they cannot again be torn asunder. This is why the discoveries of yesterday are the commonplaces of today, and why we always marvel how stupid we were not to see what post factum appears to be so obvious."

Experiments with Koko [577ff.]

"In the experiment I am going to describe, a young chimpanzee, Koko, was faced with the problem how to get a banana hung high from the wall. The only solution was to push a wooden box underneath the banana and to climb on the box. Though Koko is described by Kohler as 'just as gifted as Sultan', it took him no less than nineteen days to learn this -- whereas he had learned to rake in a banana with a stick in a few minutes. The use of sticks is part of the chimpanzee's repertory of habits -- but there are no wooden boxes lying about in the forest. However, before the experiment was started, Koko was given a small wooden box as a toy; 'he pushed it about and sat on it for a moment'. He was then removed to another cage and in his absence the banana was suspended from the wall, three or four yards away from the wooden box (the italics are Kohler's: by 'objective' he means banana):

'Koko ... first jumped straight upwards several times towards the objective, then took his rope in his hand, and tried to lasso the prize with a loop of it, could not reach so far, and then turned away from the wall, after a variety of such attempts, but without noticing the box. He appeared to have given up his efforts, but always returned to them from time to time. After some time, on turning away from the wall, his eye fell on the box: he approached it, looked straight towards the objective, and gave the box a slight push, which did not, however, move it; his movements had grown much slower; he left the box, took a few paces away from it, but at once returned, and  pushed it again and again with his eyes on the objective, but quite gently, and not as though he really intended to alter its position. He turned away again, turned back at once, and gave the box a third tentative shove, after which he again moved slowly about. The box had now been moved 10 centimetres in the direction of the fruit. The objective was rendered more tempting by the addition of a piece of orange (the non plus ultra of delight!), and in a few seconds Koko was once more at the box, seized it, dragged it in one movement up to a point almost directly beneath the objective (that is, he moved it a distance of at least three metres), mounted it and tore down the fruit. A bare quarter of an hour had elapsed since the beginning of the test.'

"All's well that ends well. But it does not. A few minutes later the experiment was repeated -- after the banana had been moved about three yards from its former position, while the box was left standing where Koko had dragged it. When Koko was led back onto the stage:

'he sprang at the new banana in the same manner as before, but with somewhat less eagerness; at first he ignored the box. After a time he suddenly approached it, seized and dragged it the greater part of the distance towards the new banana, but at a distance of a quarter of a metre he stopped, gazed at the banana, and stood as if quite puzzled and confused. And now began the tale of woe for both Koko and the box. When he again set himself in motion it was with every sign of rage, as he knocked the box this way and that, b ut came no nearer to the objective. After waiting a little the experiment was broken off.'

"This tale of woe continued for nineteen days during which the experiment was repeated at varying intervals; and even afterwards, when the new skill was firmly established at least, its performance still alternated for a while with random trials.

    "Does Koko's behaviour satisfy the descriptive criteria of insight learning?

    (a) Suddenness. yes, it does -- because at the climactic moment of the first experiment, the solution did appear suddenly and all of a piece. No, it does not -- because prior to it Koko had made several half-hearted attempts at the correct solution and yet abandoned them. (b) 'Complete solution with reference to the whole layout of the field'. The answer is, No. (c) 'Smooth, unhesitating, direct and definitive' -- on one occasion, Yes, on the others, No. (d) 'Solution precedes execution of solution' -- yes and no. (e) 'Solution retained after a single performance' -- definitely No. (f) Novelty -- yes.

    "Kohler's own comments on this experiment are revealing. Although in The Mentality of Apes he stresses that the gulf between Trial-and-Error and Insight is unbridgeable ('the contrast if absolute'), his comment on Koko's initial hesitations and fumblings with the box is: 'there is only one expression that really fits his behaviour at that juncture: it's beginning to dawn on him!' Let us note that for about ten days after that first success, Koko kept manipulating the box, sometimes aimlessly, sometimes angrily, and during this whole period 'no trace of a solution appeared, except an equivalent of the words, "there's something about that box".' In another passage Kohler says (italics Kohler's): 'It may happen that the animal will attempt a solution which, while it may not result in success, yet has some meaning in regard to the situation. "Trying around" then consists in attempts at solution in the half-understood situation.'

    "No more need to said to prove that if we apply the descriptive criteria which I have enumerated, we find a graded series from 'trying around', through the 'dawning' of the solution, to the limit case of the sudden solution. But limit cases at the end of a graded series do not require a separate set of postulates to explain them. The break in actual behaviour, the discrete and unitary character of the solution in these cases can be explained in terms which are also applicable to other forms of learning."