The entry says that in the laboratory Pfungst took the horse’s part himself, and that twenty-three people out of twenty-five raised their heads at the number they were thinking of. This piece and the next follow Chapter IV of his book, “Laboratory Tests”, which is where the case stops being about one horse. The experiments were begun in November 1904 at the Psychological Institute of the University of Berlin, while the tests in the courtyard were still running, and went on after von Osten withdrew the horse; the book was held back for them, and Stumpf thought it had “gained in permanent value” by the wait. Every quotation is from Carl Rahn’s English of 1911.

The purpose

Pfungst set out two aims. The first was “to discover whether the expressive movements noted in Mr. von Osten, Mr. Schillings, and others, were to be regarded as typical and to be found in the majority of individuals”. The second was to find out “in how far the psychical processes which I had noted in my own case and which I believed to lie at bottom of these movements, were paralleled in, and confirmed by, the introspections of others.” The conditions were made as like the courtyard as possible, except for one thing that could not be transferred and that he thought was an advantage to lose: the “affective atmosphere”, the crowd and the wonder. “One person undertook the role of questioner, another—myself—that of the horse.” The experiments fell into the same three groups as the horse’s reactions: counting and computation, the “space reactions” of up, down, right, left, yes and no, and fetching or pointing out objects.

Counting

“In the experiments in counting and computation, the questioner, standing at my right, thought with a high degree of concentration of some number (usually between 1 and 10, but sometimes also as high as 100), or of some simple problem in addition. Then I would begin to tap,—but in human fashion with my right hand, rather than with my foot—and continued until I believed that I had perceived a final signal. I thus tested, all in all, twenty-five persons, of every age and sex (including children of five and six years), differing also in nationality and occupation. None of them was aware of the purpose of the experiments. It could not escape them, to be sure, that they were being watched. It was also evident to them that the things noted were certain tensions and movements; but none of my subjects discovered what the particular phenomena were that I was looking for. Only in a few isolated instances did they report that they were conscious of any movements on their part. With the exception of two persons, they all made the same involuntary movements which were described in chapter II, the most important of which was the sudden slight upward jerk of the head when the final number was reached.”

The jerk was not always upward. Its direction depended on the posture the subject had been asked to take at the start. With the head bowed, the release came as an upward jerk; with the head bent back, as a forward movement; with the head to the right, as a movement to the left, and the reverse; lying on the back with the head supported, as “a very slight movement to one side”. Between the postures there was an upright position in which no movement, or only a tremor, could be found. From this Pfungst drew a law: “The release of muscular tension which occurs with the cessation of psychic tension, tends to bring about that position of the head (and body) which, at the time, represents the slightest amount of muscular strain.” The movements “seldom were pronounced enough to be compared to motion through a distance of one millimeter, in a very few cases only did they attain to the magnitude of one or two millimeters.” The two people who made no movement he could find were “two scientific men whose mode of thought was always the most abstract, and one of these was, in spite of repeated attempts, unable to elicit any response whatever on the part of the horse.”

The man playing the horse could do what the horse had done and more. “In the cases of the more suitable subjects I was able to indicate not only the number they had in mind, but also the divisions in which the number was thought, thus 12 as 5 and 5 and 2, or the same number as 2 and 5 and 5, and I was also able to determine the addends in the addition—i. e., whether the problem had been conceived as 3+2=5 or as 2+3=5.” He made the horse’s mistakes: a smaller jerk at a subdivision taken for the final one, so that he gave 4 for 8 and 3 for 9, “just as Hans had so often done”; the number 1 was hard to get, and so were the large numbers; 17 was read in three successive trials as 4, as 9, and as 17; “after some practice I was able to give numbers as high as 58 and 96”; and the errors of one too many and one too few recurred.

The subjects’ own accounts matched his. “The one who took the part of the horse gave three taps and made the following entry: ‘At 3 I saw a slight upward jerk of the head on the part of the questioner’. The questioner however had thought of 4, and made the following note, without knowledge of the other’s entry: ‘I was aware of extreme tension, so that it was impossible for me to get beyond 3’. Or again, the ‘horse’, reacting to a movement on the part of the questioner, stopped at 3, but the latter, having intended to obtain 2, made the following entry: ‘I noted clearly that I ceased thinking of the number too late, and did not put on the brakes, as it were, until I had arrived at 3’.” Every error was the questioner’s, as it had been in the courtyard. “The most valuable feature about these tests was that the mute horse had now been replaced, as it were, by an animal capable of speech, and that it was now possible to follow the same process both from within and from without.”

Up, down, yes, no

In the second group the subject was asked to fix his mind on one of four or six concepts, “up”, “down”, “right”, “left”, “yes”, “no”, in any order he chose, at the signal “Now!”, and sometimes to think of nothing at all; Pfungst stood opposite and named the concept. “With twelve subjects (a total of 350 tests) I made an average of 73% correct responses, and in the more favorable cases I attained even 90 to 100% correct responses. Very slight involuntary movements of the head and eyes, which showed but little individual variation, and always occurred when the subject began to fix upon the concept, were the signs which I used as cues.” “Up” and “down”, “right” and “left” moved head or eyes in those directions; “forward” moved the head forward; “yes” was “a slight nod of the head”; “no” was “two to four rapid turnings of the head to either side”; and “zero” was “a movement of the head describing an oval in the air”, so distinct that “it was even possible to discover whether the subject had conceived of a printed or a written zero.” It was not necessary to look at the subject’s face. Fixing a point to one side, so that the face fell on the edge of his retina, he still made 89 percent correct inferences in twenty tests, “not astonishing after all, when we recall that the periphery of the retina possesses a relatively high sensitivity for movement impressions”.

The subjects could not stop the movements once told of them. “It was very difficult and in some cases almost impossible for those persons whom I had initiated into the secret, to inhibit them voluntarily.” Asked afterwards what cue he had been using, “they invariably responded with probable explanations which were always wide of the mark, and those to whom I disclosed the cue—(after the experiments were completed), were thoroughly astonished.”

The artificial association

The courtyard had posed a puzzle. Hans signalled “no” and “zero” alike, with a swing of the head to the right and then the left, and Pfungst and Schillings, who had both got that answer from him without ever thinking of the horse’s movement, had evidently been making a small version of the horse’s swing in place of their own natural shake. Had the horse’s habit been copied into them without their knowing? Pfungst tried to make it happen on purpose.

He asked a subject, von A., to think of “left” or “right” in any order, and told him that instead of saying the answer he would indicate “right” by moving his arm down and “left” by moving it up, with “a fictitious but plausible reason”. “In the first three tests he moved his eyes to the right when he thought of ‘right’, and to the left when he thought of ‘left’. This was the normal expressive movement. In the fourth test, however, the thought ‘left’ was accompanied by an upward movement of the eyes. Two further tests again showed eye-movements to the right and left. In the seventh test with the idea ‘left’ the eyes moved first to the left and then immediately upward. In the following ten tests the eyes were turned regularly upward at the thought of ‘left’, and downward at the thought of ‘right’, with only one exception which was a normal movement to the left. The normal expressive movements, therefore, were displaced by the artificial, after the seventh test.”

A second subject, B., combined the old movement with the new, so that “up” became up and to the right. A third, Ch., made the head go up for “right” while the eyes still went right, and once the new habit was set Pfungst could read him from the head alone, with the subject blindfolded, 32 times in 40. Then Pfungst reversed the arms, down for “right” and up for “left”, telling the subject it was “an idle whim”; “it was only after the twelfth test that the former ‘association’ which I myself had caused to be established, was completely displaced by the new.” When he stopped moving his arm and simply spoke his guesses, the acquired movements faded and the natural ones came back; when he resumed the arm, the artificial habit came back too, “although not until some 14 tests had been made,—during which the normal movements to the right and left were often inhibited and during which the conditions were, on the whole, chaotic.”

He then did it with words that have no natural gesture at all. Miss St. was asked to think of “Ibis”, “Irbis”, “Kiebitz” and “Kürbis”, ibis, panther, plover and pumpkin, and told he would answer by arm movements forward, back, right and left; 15 of 20 trials succeeded, “without the slightest suspicion on the part of the subject … that she was giving me the necessary directives in the form of very minute movements of the head and eyes to the right and left”. She was astonished he could guess words so alike. In one trial she happened to think of the movement she expected him to make, “became confused, and as a result the number of my successful reactions suddenly fell.” With two trained subjects he made no error in thirty-five trials, and could sometimes name the word before the trial began, because the subject, deciding which to choose, made the movement while choosing. “Nothing surprised a subject more than the remark: ‘You are intending to think of the word “Kürbis”’, or ‘You had thought of concentrating your mind upon “Ibis” but later decided in favor of “Kiebitz”’, yet nothing could be more simple.” A subject who visualised poorly, Miss von L., thinking of “Form”, “Inhalt”, “Mass” and “Zahl”, form, content, measure and number, went from 10 right in the first 20 to 19 in the last 20, and “noted only a few of her upward head-movements, viz.: those that were especially pronounced (movements through about 2 millimeters), but of the others she knew nothing.” “Here our only concern was to show that unconscious change in natural expressive movements and the acquisition of artificial ones are possible in the case of psychically normal subjects trained in introspection.”

Who could work the horse

The human results also explained why some people could work the horse and most could not. The questioner who succeeded had to have “a certain measure of ability and tact in dealing with the horse”, “the power of intense concentration”, “facility of motor discharge”, so that the nervous energy went to the muscles and not to the sweat glands or the heart, and “the power to distribute tension economically”, to hold it long enough and let it go at the right moment. Few were “entirely representative of the type”, and they were “those who are commonly characterized as being of a lively temperament and strongly impulsive.” A crowd helped a questioner like von Osten, whose zeal it raised, and hurt one like Schillings, whom it distracted. “Thus Hans acquired a reputation for ‘Einkennigkeit’, that is, he would accustom himself only to certain persons. Such a reputation was hard to reconcile with his much praised intelligence.” The measuring of the jerk on smoked paper, and the sheets of paper on the floor that stood in for the coloured cloths, are in the next piece, “The smoked paper”.

Sources

• Oskar Pfungst, Clever Hans (The Horse of Mr. von Osten), translated by Carl L. Rahn, New York: Henry Holt, 1911, chapter IV, “Laboratory Tests”, pages 102 to 116, and chapter V, pages 203 to 210; every quotation in this piece is from that translation. archive.org