FOOTNOTES:

Some tried to explain the whole thing on the basis of purely mechanical memory and would thus allow the title "learned" but not "intelligent" Hans. If, for instance, he was able to indicate the component of a clang of three tones, it was not because he had the power to analyze the tone-complex, but because he was able to see the stops of the harmonica and was accustomed to give one tap for every stop which was closed. If he was able to tell time by the watch, it was not because he read it, but because he was always asked at the same hour of the day (which, of course, was contrary to fact) and because he had learned by heart the necessary number of taps. They also said that his manifold arithmetical achievements were merely the expression of a remarkable memory; that in the animal brain, lying fallow for centuries, there was stored up a tremendous amount of energy, which here had been suddenly released. They justified their point by calling to mind, in this connection, the wonderful memory of primitive races. The authors of the two monographs already mentioned, Zell and Freund, adopted this 'mnemotechnic' interpretation, and the latter considered that he had disposed definitely of the problem in designating the horse—a "four-legged computing machine."

Another group would not even allow Hans the glory of a wonderful memory. He knew nothing. Rather was he to be regarded as a stupid Hans, and totally dependent upon signs or helps given by his master. Only a very few believed, however, that such signs—the nature of which was quite unknown or regarding which only vague unsubstantiated suppositions were advanced—were given unintentionally. Most of the critics openly averred that we here had to do with intentional control,in other words, with tricks. But not only did stupid orthodoxy dispose of the matter in this way, but also the enlightened, who believe everything unusual to be contrary to reason. They put the Hans problem on a level with spiritualism, and were convinced that if the veil were removed a crass imposition would be revealed. Professional trainers who regarded themselves as well informed did not hesitate to give expression to this same view, even though they had observed Hans inadequately or not at all.

The defenders of this second point of view were not at a loss to point out the signs supposed to be given to Hans. One of these believed he had discovered the primary means for giving these signs in the slouch hat of Mr. von Osten. It was no accident, they said, that Mr. Schillings wore a slouch hat when he experimented with the horse. It is sufficient to note that Mr. Schillings was usually bare-headed or wore only a cap when he tested the horse. Another accused, in like fashion, the long coat of the experimenter; a third, who "had had opportunity to observe Hans on several occasions," declared with equal certainty that the cue lay in the movements of the hand as it was thrust into the pocket filled with carrots. One circus-star declared, that the trick lay in eye movements, another such star declared it lay in the movements of the hand. A sixth discovered that the signs were "manifold" and adds, "to be sure, the trainer must have a fund of such signs in order to prevent embarrassment." Such a hypothesis is itself, it would seem, one of embarrassment. On the other hand, there were many first-class observers who vainly tried to discover regularly recurring signs; among them the only professional trainer,—who had devoted any satisfactorylength of time to the horse and had also sought diligently for the signs in question—said, "I was fully convinced that I would be able to explain the problem in this way, but I was mistaken." The president of the "Internationale Artisten Genossenschaft," a person who knew all the usual means of control in trick performances, went over to the other side as a result of his observations.

There were others who sought for auditory signs. The opinion was expressed that "Hans was unable to answer the simplest question such as 'What is two plus three?' whenever the questioner's tone of voice differed from that of the master's." Another put chief stress upon the changing inflection; furthermore, a "high degree of auditory sensitivity" was often offered in explanation.

The sense of smell was also made to bear some burdens. With its help, for instance, Hans was believed to be able to recognize the photograph of some one present, supposing, of course, that the person had carried the picture about with him, thus allowing it to be impregnated with his peculiar personal odor. One even suggested that the heat radiating from the questioner's body and the electric stimulus conducted underground to Hans's foot were sufficient explanation for his remarkable feats.

Even the so-called N-rays, of one-day fame, which were supposed to radiate from the human brain when in activity, were offered as a solution. A similar thing may have been in the mind of the "natural philosopher" who even after the publication of the December report, wrote as follows in one of the journals: "On the basis of most careful control, I have come to the conclusion, that the brain of the horse receives the thought-waves which radiate from the brain of his master; for mental work is,according to the judgment of science, physical work." Of the same character are the explanations of two others, one of whom declares that Hans was acting "under the magnetic influence of man", while the other declared that "hypnotic suggestion is involved", and, ignoring attested facts, tells us that, "The horse can execute the commands of another only when the master, with whom it is 'en rapport', wills that it shall obey." We may close the catalogue of explanations with one more, which, in spite of its vagueness, found many defenders, viz: suggestion. Without defining this conception more specifically and without the slightest notion of the peculiar difficulties which it involves (L. Loewenfeld in his "Handbuch des Hypnotismus" [Wiesbaden, 1901, pp. 35ff.] cites twenty different definitions of the term given by as many authors) a critic writes: "The astounding phenomenon of an animal apparently possessing human reason is to be attributed solely to suggestion". Having referred to a dog trained for the vaudeville-stage, the gentleman concludes that, "our intelligent horse, as well as the dog, is simply of fine nervous organization and hence highly susceptible to suggestions".

What was to be done, with this mass of conflicting explanations? Everyone considered his own opinion the only correct one, without, however, being able to convince anyone else. The need here was not simple affirmation, but proof.

FOOTNOTES:[A]"Frankfurter Zeitung" of September 22, 1904: "Concerning the question whether the horse was given some sort of aid, Professor Stumpf expressed himself freely. He said: 'We were careful to state in our report that the intentional use of the (actual) means of training, on the part of the horse's teacher, is out of the question, ... nor are there involved any of the known kinds of unconscious, involuntary aids. Our task was completed after we had ascertained that no tricks or aids of the traditional sort were being employed'." After some remarks on unconscious habituation and self-training on the part of animals, the writer arrives at the conclusion that "the horse of Mr. von Osten has been educated by its master in the most round-about way, in accordance with a method suited for the development of human reasoning powers, hence in all good faith, to give correct responses by means of tapping with the foot. But what the horse really learned by this wearisome process was something quite different, something that was more in accord with his natural capacities,—he learned to discover by purely sensory aids which are so near the threshold that they are imperceptible for us and even for the teacher, when he is expected to tap with his foot and when he is to come to rest."[B]"From the productions of the 'thought-readers' we see how slight and seemingly insignificant the unconscious movements may be, which serve as signs for a sensitive re-agent. But in this case no contact is necessary. There would have to be some sort of visible or audible expression on the part of the questioner. No proof for this has as yet been advanced."How any one possessing the power of logical thought could possibly infer from these words of mine (published in the above-mentioned article in the "Tag"), that I denied the possibility of the occurrence of visual signs, is to me incomprehensible. What I did deny, and still deny, is that up to that time any had been proven to occur.[C]Since the present treatise is intended for the larger public, this brief resumé will probably be welcome to many.[D]Ideas are copies of former sensations, feelings and other psychic experiences and retain also the accidental signs which belonged to those earlier experiences. They are images in the concrete, such as the memory of a certain horse in a certain definite situation ... say a well fed, long-tailed one standing at a manger. A concept, on the other hand, is a mental construct which has its rise in ideas, or memory-images, in that their essential characteristics are abstracted. For this reason the concept has not a definite image-content. (Thus the thought of "horse" in general, is a concept. Not so the thought of a certain individual horse,——that is an idea, with a definite image-content.)[E]All examples mentioned are cited from extant works of various observers.[F]The works referred to in the text are to be found listed onpages 267 ff.

[A]"Frankfurter Zeitung" of September 22, 1904: "Concerning the question whether the horse was given some sort of aid, Professor Stumpf expressed himself freely. He said: 'We were careful to state in our report that the intentional use of the (actual) means of training, on the part of the horse's teacher, is out of the question, ... nor are there involved any of the known kinds of unconscious, involuntary aids. Our task was completed after we had ascertained that no tricks or aids of the traditional sort were being employed'." After some remarks on unconscious habituation and self-training on the part of animals, the writer arrives at the conclusion that "the horse of Mr. von Osten has been educated by its master in the most round-about way, in accordance with a method suited for the development of human reasoning powers, hence in all good faith, to give correct responses by means of tapping with the foot. But what the horse really learned by this wearisome process was something quite different, something that was more in accord with his natural capacities,—he learned to discover by purely sensory aids which are so near the threshold that they are imperceptible for us and even for the teacher, when he is expected to tap with his foot and when he is to come to rest."

[B]"From the productions of the 'thought-readers' we see how slight and seemingly insignificant the unconscious movements may be, which serve as signs for a sensitive re-agent. But in this case no contact is necessary. There would have to be some sort of visible or audible expression on the part of the questioner. No proof for this has as yet been advanced."How any one possessing the power of logical thought could possibly infer from these words of mine (published in the above-mentioned article in the "Tag"), that I denied the possibility of the occurrence of visual signs, is to me incomprehensible. What I did deny, and still deny, is that up to that time any had been proven to occur.

How any one possessing the power of logical thought could possibly infer from these words of mine (published in the above-mentioned article in the "Tag"), that I denied the possibility of the occurrence of visual signs, is to me incomprehensible. What I did deny, and still deny, is that up to that time any had been proven to occur.

[C]Since the present treatise is intended for the larger public, this brief resumé will probably be welcome to many.

[D]Ideas are copies of former sensations, feelings and other psychic experiences and retain also the accidental signs which belonged to those earlier experiences. They are images in the concrete, such as the memory of a certain horse in a certain definite situation ... say a well fed, long-tailed one standing at a manger. A concept, on the other hand, is a mental construct which has its rise in ideas, or memory-images, in that their essential characteristics are abstracted. For this reason the concept has not a definite image-content. (Thus the thought of "horse" in general, is a concept. Not so the thought of a certain individual horse,——that is an idea, with a definite image-content.)

[E]All examples mentioned are cited from extant works of various observers.

[F]The works referred to in the text are to be found listed onpages 267 ff.

Theobservations on the horse under ordinary conditions would have been quite insufficient for arriving at a decision as to the tenability of the several possible explanations. For this purpose experimentation with controlled conditions was necessary.

It was necessary, first, that the place in which the experiments were performed should be guarded against sources of error and interruptions. Several difficulties stood in the way of the removal of the horse to a more convenient place. Therefore, a large canvas tent was erected within the courtyard of Mr. von Osten. This afforded the necessary isolation without hindering the free movements of the horse. After the essential part of the experiment had been completed and the problem had been practically solved, experimentation was sometimes conducted in the open courtyard. A number of the experiments were also performed in the horse's stall.

The choice of proper persons to experiment with the horse required careful consideration. In so far as observations were to be made upon the questioner, Mr. von Osten was of course indispensable. But to obviate every objection he, as well as Mr. Schillings, had to be excluded from the greater part of the experiments, andother persons had to be selected who could learn to handle the horse. Now one would have thought that the horse would respond to any moderately efficient examiner. But as a matter of fact it was found that the horse would not react at all in the case of the greater number of persons. Again, in the case of others he would respond once or twice, but would then cease. All told, Hans responded more or less readily to forty persons, but it was only when he worked with Mr. von Osten or with Mr. Schillings, that his responses were at all dependable. For this reason I undertook to befriend the horse, and by happy chance it came to pass in a short time he responded as readily to my questions as to those of the two gentlemen. In a few of these experiments the Count zu Castell, Count R. von Matuschka and Mr. Schillings undertook the rôle of questioner. Where these are not mentioned in the results here published, I myself did the questioning.

With regard to the number of experiments and their performance, the following precautions were observed. A sufficiently large number of tests was made in each series in order to obviate the possibility of the contention that the horse's errors were due to chance. The conditions of experimentation were such that the further contention that he happened to be tired or otherwise indisposed, whenever the reactions seemed to be inadequate, could not be offered. The possibility of confusing the horse by means of unwonted conditions also had to be avoided. For this reason it was necessary to alternate the trial in which procedure was with the knowledge of the answer on the part of the questioner, with the trial in which the procedure was without such knowledge. Such precautions had hitherto been neglected, and therefore those negative results which had been occasionally obtained in single trials, could not claim objective validity, even though the persons making the tests were subjectively convinced.

The course of the experiments was determined by the nature of the problem itself. By means of a very simple test it was possible to discover whether or not Hans was able to think independently. He was confronted with problems in which the procedure was without knowledge of the answer on the part of the questioner. If under these conditions he could respond with the correct answer—which could be the result of a rational process only—then the conclusion that he could think independently, was warranted. The examination would be closed and Mr. von Osten would be justified in all he claimed for the horse. If, however, Hans should fail in this test, then the conclusion that he could think was by no means warranted, but rather the inference that he was dependent upon certain stimuli received from the questioner or the environment. Further investigation would be for the purpose of discovering the nature of these stimuli.

To ascertain by means of which sense organ or organs the horse might receive these necessary stimuli, the method of elimination was employed. We began by excluding visual stimuli by means of a pair of very large blinders. Should this investigation be without results, then we would proceed to test the sense of hearing. The elimination of auditory stimulations would be more difficult, because ear-caps or the closing of the passage by means of cotton would not give sufficient assurance that the sound-waves were being interrupted, even if the horse were docile enough to suffer these appliances. Thereupon would follow the testing of the sense of smell and of the skin-senses. And finally there might be involvedanother still unknown sense, such as seems to exist in the lower animal-forms. The reader therefore can readily see that the investigation might possibly have become very complex, and that the investigator had to be prepared for all of these possibilities.

The results of the experiments and the essential circumstances under which they were conducted, were in every case recorded immediately.

It goes without saying that in the final formulation of the results, all values—including those which were not consonant with the majority—were to be used.

During the course of these experiments Hans wore his accustomed trappings, i. e., a girdle, light headgear and snaffle, and he either stood alone, untied, or was held loosely by the bridle either by the questioner or (though only in a few instances) by his attendant. The questioner always stood to the right of the horse, as Mr. von Osten had been accustomed to do. As reward for correct responses Hans received from the questioner[G]—and from him only—a bit of bread or carrot, and at times also a square of sugar. Never was a whip applied. From time to time the horse was led about the courtyard or was allowed to run loose in order to secure the needful respite. Besides myself there was usually present Prof. Stumpf and Dr. von Hornbostel, who kept the records, and frequently also Mr. von Osten. Several times I worked alone with the horse. The results obtained in the horse's stall were in no respect different from those got in thecourse of the experiments carried on in the courtyard. Whenever a doubt arose as to the number of taps made by the horse (though this did not frequently occur), then the series in question was immediately repeated.

In this report of the results of our experiments, the reader must bear in mind that it was impossible to adhere to that order and distribution of tests which we are wont to require in the case of psychophysical experiments conducted under regular laboratory conditions. All sorts of difficulties had to be overcome: unfavorable weather, the crowds of curious ones, certain peculiarities of the horse—such as shying whenever the wind rippled the canvas of the tent—and last but not least, the idiosyncrasies of Mr. von Osten who repeatedly attempted to interrupt the progress of the experiments.

Since it was evident that different kinds of processes were involved in solving the problems and since the solutions would be indicated by tapping, or by movements of the head, or by walking over to the object to be designated, the results of these three sets of experiments have been grouped under three corresponding heads.

The following tests were made in which the method was such that when the problem was presented to the horse, the correct solution was known to none of those present, least of all to the questioner. This method we shall designate in the following report as "procedure without knowledge" whereas we shall call the method in which the answer was known to the questioner, "procedure with knowledge".

In order to discover if the horse could read numbers,a series of cards on which numerals were blazoned, were exposed to the horse's view in such a way that none of those present was able to see them, and the horse was asked to tap the numbers as they were shown. This experiment was repeated at different times and in all there were 49 tests in which procedure was without knowledge, and 42 in which procedure was with knowledge. In the case of the former there were 8% correct responses, whereas in the case of the latter 98% of the answers were right. As an example of the course which the series tended to take, we insert the following, in which Mr. von Osten himself acted as questioner.

Method.No. exposed.No. tapped.Withoutknowledge814With"88Without"48With"44Without"79With"77Without"1017With"1010Without"39With"33etc.

Whenever the questioner knew the solution, nearly all of the horse's answers were correct; but when the answers were unknown to the questioner, the horse's responses were, with only a few exceptions, quite unsuccessful. Since the few exceptional cases must be regarded as fortuitous, the conclusion is warranted that the horse was unable to read numerals without assistance.

In order to discover whether the horse could read words such as "Hans" or "Stall" or the names of colors, they were written upon placards and hungup in a row before the horse in such a way that the questioner could see the individual word but could not immediately recognize the particular place that each one occupied in the series. The horse was then asked: "Upon which placard is the word'Hans'?", "On which is the word 'Stall'?", etc. In order to make sure, he was required to repeat each answer.

Then the experimenter would determine for himself the place of the word in the series and would ask the question again. Fourteen such tests, in which the procedure was with knowledge on the part of the questioner, were interspersed with twelve in which the procedure was without such knowledge. With the latter there were no correct responses, whereas in the cases of procedure with knowledge 100% of the answers were correct. Evidently the horse could not read words.

Three words were thereupon whispered in his ear, which he was asked to spell in accordance with the method described onpage 21. Since he had to indicate first the row, and then the place in the row occupied by the letter, it took two answers to indicate the position of each letter. I acted as questioner. The ordering of the table of letters was unknown to me, except the position of the letter "a", which naturally came first, and the place of the letter "s", concerning whose position I had purposely inquired. The words chosen for this experiment were "Arm", "Rom" (Rome) and "Hans". The horse responded incorrectly in the case of every letter which was unknown to the questioner. "A" and "s" alone were given correctly. Thus in spelling the word "Rom" the horse responded with the series 3, 4; 3, 4; 5, 4; 5, 4; i. e. "jjst", instead of the correct series: 4, 6; 4, 2; 3, 7. I later selected three other words, the spelling of which involved the tapping of thirty-two numbers on the part of Hans, and whose position I had carefully ascertained beforehand. When these were given to the horse to spell, he responded promptly without a single error. Evidently Hans was unable to spell without assistance of some sort from the questioner.

The horse's reputed aptitude in computation was tested in the following way. Mr. von Osten whispered a number in the horse's ear so that none of the persons present could hear. Thereupon I did likewise. Hans was asked to add the two. Since each of the experimenters knew only his own number, the sum, if known to anyone, could be known to Hans alone. Every such test was immediately repeated with the result known to the experimenters. In 31 tests in which the method was procedure without knowledge, 3 of the horse's answers were correct, whereas in the 31 tests in which the method was procedure with knowledge, 29 of his responses were correct. Since the three correct answers in the cases in which procedure was without knowledge evidently were accidental, the results of this series of experiments show that Hans was unable to solve arithmetical problems.

For the purpose of discovering whether the horse could at least count, the Russian kindergarten device, which Mr. von Osten had used in training, was utilized. The machine was placed before the horse, but the experimenter turned his back upon it. Before each test, a number of balls were pushed to one side and Hans's problem was to indicate the number thus separated. Each test was repeated with procedure with knowledge. Of eight such experiments Hans responded successfully every time procedure was with knowledge but failed every time procedure was without knowledge. Thus 7 balls were at onetime designated as 9 and later as 14, while 6 were at first designated as 12, and later as 10. Since all these errors could not be accounted for on the ground of miscounts on the part of the horse, it was evident that Hans is quite unable to count.

The memory-test was conducted in the following manner. In the absence of the questioner a number or the name of some day of the week was spoken to the horse. The experimenter would then return and question him. Of 10 responses 2 were correct, 8 incorrect. Among the correct answers were the number 3, a number which, as we shall see, Hans was prone to give under all sorts of conditions, and which therefore meant very little when given as a correct response. The number 2, on the other hand, was consecutively indicated by 7, 9, 5, and 3, 8 was given as 5, 6, 4, and 6, consecutively; and finally Wednesday was indicated as the fourteenth day of the week. After this we undertook the test the horse's far-famed knowledge of the calendar. Dates, such as Feb. 29, Nov. 12, etc., were given to Hans and he was asked to indicate on which day of the week they fell. Sunday was to be indicated by 1, Monday by 2, etc. Of 14 such tests, 10 were unsuccessful, 4 successful. But in the case of these 4 something very interesting occurred. It happened that during this series the keeper of the horse was present, and he happened to know the days on which these dates fell,—as he himself testified. The dates in question were also little more than a week or so from the day of the experiment, so they could easily be determined. But as soon as we took more remote dates both man and beast were hopelessly lost. It was certain that Hans had no knowledge of the calendar. It is needless to say anything of his supposed knowledge of cards andcoins. Hans plainly was incapable of the astonishing feats of memory which had been claimed for him.

Finally we investigated Hans' musical ability. In a room adjoining the horse's stall there was a small harmonica, which spanned the once accented octave. On this one or more tones were played. The horse was required to indicate the tone played, the number of tones played and their relation to one another. For testing his general hearing 20 tests were given in which the method was procedure without knowledge. Of the responses only one was correct, and that one was the tone e, for which the proper response was three taps, but we must bear in mind what has already been said of the number 3. The tone b was indicated by 11 taps, although Hans had only learned a scale of one octave and therefore could respond to only seven tones. In the tests in which the method was procedure with knowledge, he again, without exception, was successful. Similar results were obtained in the analysis of compound clangs. In the cases of procedure without knowledge (although the experimenter here knew the correct responses, he purposely refrained from thinking of them) not a single response was correct; while in the cases of procedure with knowledge, all but one were correct. The following were typical responses: Three tones were played and the question was asked, "How many tones were played?" Hans responded first with 4 taps and then with 1. The tones c, e, g, a, (1, 3, 5, 6) were struck and the question asked, "Which tone must be eliminated to make the complex a chord?" In the tests in which the method had been procedure with knowledge, this question had always been answered correctly, but when procedure was without knowledge the responses were first 13, a tone which doesnot exist for Hans, then 2, a tone which was not given in the clang to be analyzed, and finally 3, which was not the discordant tone. Hans's far-famed musical ability was an illusion.

Taking the results of all the tests into consideration, we find that in the case of procedure with knowledge, 90 to 100% of the responses of the various series were correct, whereas, in those series of procedure without knowledge 10%, at most, of the responses were correct. Under the conditions prevailing during these latter tests, even these 10% must be regarded as due to chance. To be sure Mr. Grabow, a member of the school board and an enthusiastic follower of Mr. von Osten (Zeitschrift für Pädagogische Psychologie, Pathologie und Hygiene, Berlin, 1904, Jahrg. 6, Heft. 6, S. 470), mentions a large number of successful tests, which were supposedly made in accordance with the method of procedure without knowledge. A thorough analysis of his experiments was not possible, because the conditions under which they were conducted were not adequately specified. But I have no doubt that the successful responses of the horse were due solely to the absence of precautionary measures. I, too, could cite a number of seemingly correct responses which demonstrably were due to the absence of adequate precautionary measures. I therefore repeat: Hans can neither read, count nor make calculations. He knows nothing of coins or cards, calendars or clocks, nor can he respond, by tapping or otherwise, to a number spoken to him but a moment before. Finally, he has not a trace of musical ability.

After all this experimentation it was evident that the horse was unable to work alone, but was dependent upon certain stimuli from its environment. The questiontherefore arose: does the horse get these stimuli while the question is being put, or during his responses, i. e., during the process of tapping.

If Mr. von Osten's opinion was correct, then the process of questioning played an important part in the success of the experiment. Of course, as he said, it was not necessary to ask the question aloud; it was sufficient—curiously enough—that it be inwardly spoken, thanks to the horse's extraordinary auditory sensitivity. If, however, conditions were made such that the auditory sense was eliminated, then the animal would be unable to respond. Such a theory is not quite as absurd as it might seem at first blush. For Hansen and Lehmann have shown that an acute auditory organ is able to respond to such delicate stimulation as is involved in the softest whisper, or even in the so-called nasal whisper in which the lips are tightly closed.[3]They have attempted thus to explain any modes of supposed "thought-transference", (cf.page 7). Since experts on horses agree that the horse has acute auditory sensitivity, Mr. von Osten seized upon this fact and tried to establish his theory in the following manner. No response was successfully made on the part of the horse, he said, when the sound waves caused by his (Mr. von Osten's) inner speech were deflected from the ear of the horse. This was the case when he closed nose and mouth while inwardly putting the question, or deflected the waves from the horse's ear by means of a placard held before his mouth while speaking, or finally by applying lined ear-muffs to the horse's ears. If, on the other hand, he closed only his nose and not his mouth while thus inwardly putting the question, or if he held the placard so that there was a possibility of deflecting the sounds to the horse's ear, or if the ear-muffs were of too sheer a material, then Hans could hear and answer the questions which for human ears were inaudible. He demonstrated all this by means of experiments and of 20 tests of the first kind, in which auditory sensations were supposedly eliminated, 95% of the responses were incorrect (Hans would always tap too great a number); whereas of 28 tests of the second kind, not a single answer was wrong, just as had been predicted. Now I have repeated both kinds of tests, but have always found some correct responses in those cases in which the horse, supposedly, was unable to hear, a thing which greatly astonished Mr. von Osten. In fact, the responses of the horse were quite as correct when I did not even whisper the question inwardly. It was quite clear that putting the question in any form whatever was wholly unnecessary. Mr. von Osten's demonstrations to the contrary, which were based upon erroneous physical principles, are to be explained as cases of vivid autosuggestions, (but of this, more inChapter V). After all this experimentation, it was manifest that the cue was not given to the horse while the question was being put; it occurred, therefore, at some time during the process of tapping. But by means of which sense organ was it received by the horse?

We began by examining the sense of vision, and in the following manner. Blinders were applied, and it is worthy of mention that Hans made no attempt to resist. The questioner stood to the right of the horse, so that the animal knew him to be present and could hear, but not see him. Hans was requested to tap a certain number. Then the experimenter would step forward into the horse's field of vision and would put the same problem again. Since, in the tests of the first kind, Hans wouldalways make the most strenuous efforts to get a view of the questioner, and since he would rave and tear at the lines whenever the attempt was made to tie him,—a thing which he had never done hitherto,—it was impossible to determine in some cases whether or not he had seen the questioner during the process of tapping. I am using, therefore, in the following exposition, besides the two categories of "not seen" and "seen", a third which I have called "undecided". A total of 102 tests were made in which large blinders were used. In 35 of these, the experimenter certainly was "not seen" in 56 cases he was "seen" and the remaining 11 are "undecided". Under the first of these categories 6% of Hans's answers were correct (i. e. only two), under the second head 89% were correct and under the third 18% were right. In other words, the horse was at a loss the moment he was prevented from seeing the questioner; whereas his responses were nearly always correct when the experimenter was in sight, certain proof that the horse's failures are to be attributed to the elimination of visual stimuli and not to the general inconvenience occasioned by the blinders. It is evident therefore, that the horse required certain visual stimuli or signs in order to make a correct response.[H]

Such unequivocal results, however, were only obtained after we had provided blinders of sufficient size (15 × 15 centimeters). Mr. von Osten believing that the horse would not suffer these to be applied, had at first proposed other measures. He held a slate before his face. Some of the horse's responses were right, others wrong. The tests were repeated and were successful as long as I, myself, held the slate before my face, but not a single one of the responses was correct when another would attempt to hold the slate before me. Mr. von Osten then brought forth a kind of bolster which he fastened on the right side of the horse's face,—the side which was turned toward the questioner. But this also gave uncertain results. Finally he agreed to apply blinders. But these were much too small and projected at a great angle from the head (Mr. von Osten had cut the straps, for he thought they worried the animal). The result was that only the posterior part of the horse's normal field of vision was obstructed. Therefore, one could never be quite sure whether Hans, who—it will be borne in mind—made every attempt to see the questioner, had not perhaps after all been able to peer over the edge of the blinder. The number of "undecided" tests, therefore, became very great. Of 108 tests, only 25 could be placed in thecategory of "not seen", 44 in the "seen", and 39, i. e., a third of the total, in the "undecided." The percentage of correct answers for these three categories were, respectively: 24%, 82% and 72%. Here we have once more approximately the same ratio between the categories of "seen" and "not seen" as in the case of the tests with the smaller blinders. If we were to count the cases which we had put under the head of "undecided," in the same category as those in which vision had been excluded—as Mr. von Osten had done—then one would have been led to the conclusion that the horse did not need visual signs. Several observers had thus been led astray: e. g., General Zobel writes in the "National-Zeitung" (Aug. 28, 1904), that upon request Mr. von Osten had covered Hans's right eye "by means of some sort of blinder, so that he was unable to see his instructor", and that Hans did not fail to respond correctly. We evidently have here to do with the unreliable bolster mentioned above. Furthermore, Mr. Schillings made a number of tests with the small blinders, in which 50% of the answers were correct, and probably in the same manner were obtained the results published in one of the daily papers (the "Berliner Tageblatt", Dec. 12, 1904), several days after the publication of the December report, and reading as follows: "Tests have been made upon Hans with blinders over his eyes and it is to be noted that, in spite of these, he still responds correctly." Mention is also made of the experiments noted inSupplement III (page 257), in which Mr. von Osten hid behind the questioner and merely encouraged the animal by occasional exhortations, but it is not possible to say with any degree of certainty in how far he was really hidden from the horse's view.

I would add that the horse—in so far as it was at all possible to decide—never looked at the persons or the objects which he was to count, or at the words which he was to read, yet he nevertheless gave the proper responses. But he would always make the most strenuous efforts to see the questioner. (Seepage 43). I would furthermore add that several experiments, in which Mr. von Osten and the horse were separated from each other by means of the canvas tent, failed completely, and that, on the other hand, all tests were successful in which the questioner was present in the feed-room and the door between this and the horse's stall was opened wide enough for him to be seen by the horse. I would also mention that toward evening the responses became less and less accurate. The conclusion that visual stimuli were here operative cannot be gainsaid.

It was possible, to be sure, that other senses might also be involved, but it was certain that auditory sensations did not enter it. This is shown by the fact that one might remain just as silent while the horse was tapping his answer as during the putting of the question and yet obtain a correct response. Hans, furthermore, could scarcely be distracted by auditory stimulations. If either the experimenter or anyone else present sought, at a given moment, to interrupt him by such calls as "Halt", "Wrong", etc., while he was going through the process of tapping, they very seldom succeeded in their attempt. Even though such interruption did succeed in seven out of the twenty-one cases in which it was tried, the assumption is well grounded that the success was due entirely or almost entirely to minimal movements involuntarily executed by those attempting the interruption. It is to such minimal movements that the horse, as we shallsee later, promptly reacted. When the experimenter (Pfungst), himself, made the interjections, which certainly should have been more effective, we found that the horse was actually disturbed in only two of the fourteen cases; and finally in ten consecutive cases of attempted interruption not a single one was successful. There was almost a complete absence of any ear movements on the part of the horse, a fact in which I have been borne out by Mr. Henry Suermondt, the distinguished horseback rider. Indeed, I cannot recall that Hans ever turned his ears toward me, a fact which is strikingly curious in the case of a horse so attentive and so spirited in temper.

Finally, I might also mention that the breathing of the experimenter in no wise influenced the outcome of the experiment. Whether he held his breath or breathed on the leg or body of the horse, made no difference.

Investigations of the other senses became needless, for I had, in the meantime, succeeded in discovering the essential and effective signs in the course of my observations of Mr. von Osten. These signs are minimal movements of the head on the part of the experimenter. As soon as the experimenter had given a problem to the horse, he, involuntarily, bent his head and trunk slightly forward and the horse would then put the right foot forward and begin to tap, without, however, returning it each time to its original position. As soon as the desired number of taps was given, the questioner would make a slight upward jerk of the head. Thereupon the horse would immediately swing his foot in a wide circle, bringing it back to its original position. (This movement, which in the following exposition we shall designate as "the back step", was never included in the count.)Now after Hans had ceased tapping, the questioner would raise his head and trunk to their normal position. This second, far coarser movement was not the signal for the back-step, but always followed it. But whenever this second movement was omitted, Hans, who had already brought back his foot to the original position and had thereby put it out of commission, as it were, would give one more tap with his left foot.

If it was true that these movements of the questioner guided the horse in his tapping, then the following must be shown: First, that the same movements were observed in Mr. von Osten in every case of successful response; secondly, that they recurred in the same order or with only slight individual changes in the case of all who were able to obtain successful responses from the horse, and that they were absent or occurred at the wrong time in all cases of unsuccessful response. Furthermore, it was observed that it was possible to bring about unsuccessful reactions on the part of the horse as soon as the movements were voluntarily suppressed, and conversely, that by voluntarily giving the necessary signs the horse might be made to respond at pleasure; so that anyone who possessed the knowledge of the proper signs could thereby gain control over the process of response on the part of the horse. These requirements have all been fulfilled, as we shall see in the following pages.

With regard to the regular recurrence of the movements noticed in the case of Mr. von Osten, I was, after some practice, able to note carefully their peculiar characteristics. This was rather difficult, not only on account of their extreme minuteness, but also because that very vivacious gentleman made sundry accompanying movements and was constantly moving back and forth. To abstract from these the essential and really effective movements was truly difficult. It was much easier to observe these movements in the case of Mr. Schillings, probably on account of the fewer accompanying movements and perhaps on account of their greater distinctness. Usually he would raise the entire trunk a trifle, so that the movements could be noticed from behind. Besides these, I had an opportunity to observe the Count zu Castell, Mr. Hahn and the Count Matuschka. All three made the same movements, though somewhat more minutely than Mr. Schillings, yet none was as slight as those of Mr. von Osten.[I]I further noticed that Count Matuschka and Mr. Schillings often showed a tendency to accompany every tap of the horse with a slight nod of the head, the last being accompanied by a more pronounced nod and then followed by the upward jerk of the head, in other words, they beat time with the horse. In the case of the last three mentioned, for whom the horse responded far less effectively than for Mr. von Osten or Mr. Schillings, belated or precipitate jerks would frequently occur. This was found to be true in the case of all other persons who had failed to elicit adequate responses from the horse. Often, in both cases, a complete absence of any kind of minimal movement had been noted. The accuracy of these observations in the case of Mr. von Osten is attested by Mr. Stumpf and Mr. von Hornbostel, and by these same gentlemen and Prof. F. Schumann in the case of Mr. Schillings and myself. They also found these movements to be most minute in the case of Mr. von Osten. In my case also they pronounced them "minimal, and often quite imperceptible". All other persons who have seen me work with the horse, but who were not familiar with the nature of these movements, never perceived them, no matter how closely they observed me.

Since the doubt was expressed that these movements did not precede but followed closely upon the back-step of the horse (i. e., that an error with regard to the time-element was involved), it became important that time measurements be taken. This was done in the following manner: The questioner asked the horse to tap numbers from 5 to 20, seldom higher. He purposely refrained from pronouncing the number, but recorded it after each test had been completed. This was a matter of indifference to the horse (seepage 42), and had the advantage that the measurement was not influenced by knowledge on the part of the time-keeper. Two observers were required, one watching the horse, the other the questioner. Both observers had fifth-second stop-watches. The larger face of this watch shows the fifth-second and a hand on the smaller face indicates the minute. By pressing upon the stem the watch may be set in motion at any moment desired, and by pressing it once more it may be instantly stopped, and the timeelapsing betweenthe setting in motion and the stopping may be read on the face. By pressing upon the stem a third time the hands are brought back to zero, and the watch is ready for another test. At a moment agreed upon beforehand—usually the third tap of the horse—both observers started their watches. Practice tests had shown that this could be done with all the accuracy necessary in this case. As soon as the observer of the questioner noticed the latter's head movement he stopped his watch, and as soon as the observer of the horse noticed the latter's back-step he stopped his watch. Since the movement of the horse's foot does not occur as a jerk, but is of greater extent than a jerk would be, it was agreed that the observer was to stop the watch as soon as he recognized the back-step as such, not when the foot was being raised from the ground, because it was not then evident whether the horse would bring it back to the original position or whether he was preparing to give another tap, nor when he had brought his foot completely back, but at the moment in which it was evident that the horse intended to make the back-step. Experimentation had shown that an agreement as to this moment was possible. A tap with the left foot, which might possibly follow upon the back-step, could be left out of account. The difference in time between the two watches would show the time between the head-jerk of the questioner and the back-step of the horse,[J]and if the back-step was indeed a reaction uponthe head-jerk, then the watches would have to show a later time for the back-step than for the head-jerk.

Measurements of this kind were taken for Mr. von Osten, Mr. Schillings and myself. In the case of the first two it was taken without any knowledge on their part. They did not even know that they were being observed, having been told that the measurements were for the sake of determining the horse's rate. In my case, to be sure, the time could not be taken without my knowledge. I succeeded, however, in eliminating the effect of this knowledge on my part. (Cf. pages88and145.) Since the results obtained in the case of Mr. Schillings quite agree with those obtained in my case, it is evident they may be considered as being of equal value.

With regard to the number of tests the following table may be referred to. The first vertical column gives thename of the questioner, i. e. the person operating with the horse. The four other columns give the number of tests made upon each of these. The name of the person who made the observation in each series is indicated at the head of the column. It is unnecessary to give the name of the observer of the horse, for the only difficulty lay in the observation of the questioner. The numerals I and II indicate two series taken at different times.

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