Chapter II: Experiments and Observations (1)

A. EXPERIMENTAL CONDITIONS

The observations 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, and other 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 role 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 involved another 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.

B. EXPERIMENTAL RESULTS

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 the course 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.

[Footnote G: The expressions _questioner_ and _experimenter_ are used
interchangeably in this treatise.]

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.

_I. Problems solved by tapping_

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.

Without knowledge 8 14
With " 8 8
Without " 4 8
With " 4 4
Without " 7 9
With " 7 7
Without " 10 17
With " 10 10
Without " 3 9
With " 3 3 etc.

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 hung up 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 on page 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 one time 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 and coins. 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 does not 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 fuer Paedagogische 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 question therefore 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 in Chapter 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 would always 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]

[Footnote H: Throughout this treatise I am using the word "sign," or
"signal," whereas all other writers who have touched upon the
Hans-problem, have always spoken of "aids." Following von Sanden,[4]
however, I would distinguish clearly between the two. I would
designate as aids all immediate stimulations of the horse's body (i.
e. by means of contact), which have been designed with reference to
the animal's physiological movement-mechanism in such a way that
they truly 'aid' him in the production of the required movements. I
would regard as signs on the other hand, all stimulations (whether
mediate or immediate) which are selected without especial regard to
the anatomy or physiology of the horse, and bear no inseparable
relation to the thing to be done but are associated with it at the
will of the trainer. The rider's use of reins, and control by means
of leg-pressure and manner of sitting in the saddle, and the
driver's use of the lines,----all these, then are aids. A simple
pull at the reins, however, is not an aid, but a sign. The whip may
be used for giving signs as well as aids,----the latter, when it
does the work of the spur or of the pressure with the knees, as is
the case with ladies' riding-horses and in lunging. All calls and
all movements of the hand or head merely, on the part of the
trainer, are to be regarded as signs.]

Such unequivocal results, however, were only obtained after we had provided blinders of sufficient size (15 x 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 the category 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 in Supplement 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. (See page 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 shall see 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.

[Footnote I: During the tests Mr. von Osten nearly always wore a
slouch hat with a wide rim. The rim, of course, always moved with
the head, and made the movements appear on a larger scale, (in the
ratio of about 3:2, as I was able to ascertain later by graphic
methods). But observation was successful, even at a distance of a
meter and a half, when he worked with head uncovered. And even if
head and forehead were covered entirely, it was still possible to
note the movements by watching the eye-brows. When Mr. Schillings
and the rest of us worked with the horse, we either went bare-headed
or wore only a very small cap.]

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 (see page 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 time elapsing between the 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 upon the head-jerk, then the watches would have to show a later time for the back-step than for the head-jerk.

[Footnote J: For the benefit of those who are familiar with
reaction-time experiments of this kind, I would state the following:
The reaction to the head-jerk, on account of the minuteness of the
latter, was sensory throughout, and therefore all precipitate
reactions are entirely wanting. The reaction to the back-step was,
like the preceding one, a reaction to a visual cue. (Hans's tapping
was almost quite inaudible). Both stop-watches were carefully
regulated. In order to eliminate also the constant error which might
possibly arise as a result of some difference in the functioning of
their pressure-mechanism, the two watches were always exchanged in
the different series of tests, by the observer of the man and the
observer of the horse. The two time-measurements obtained by the two
observers contained, of course, the reaction-times of the observers
themselves. In order to equalize the constant error which thereby
arose, it was arranged that each observer should react alternately
now to the man, now to the horse. In order to be perfectly safe, the
reaction-times of those concerned, (von Hornbostel, Pfungst,
Schumann and Stumpf), were later determined in the laboratory by
means of the carefully regulated Hipp chronoscope. Separate
determinations were made of the reactions to the head-jerk and to an
imitation of the horse's back-step. Then the time which one observer
took to react upon a head-jerk, was compared with the reaction-times
of the other observers to the back-step. Since the greatest
difference which was found in this comparison, did not exceed
one-tenth second, the results obtained in the courtyard required no
correction.]

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. pages 88 and 145.) 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 the name 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.

-----------------+----------+----------+----------+----------
| v. H. | Pf. | Schu. | St.
-----------------+----------+----------+----------+----------
Questioner. | I II | I II | I II | I II
-----------------+----------+----------+----------+----------
v. Osten | 9 15 | 34 17 | - -- | 8 27
-----------------+----------+----------+----------+----------
Schillings | - -- | 19 17 | 6 16 | - --
-----------------+----------+----------+----------+----------
Pfungst | 6 13 | -- -- | - -- | 9 --
-----------------+----------+----------+----------+----------

We have omitted from this table several tests in which the observer of the questioner noticed no head jerks whatever, and therefore could not arrest his stop-watch, although the horse responded correctly. Four tests of this kind were made by Mr. von Hornbostel, two by Mr. Pfungst, two by Mr. Schumann and five by Mr. Stumpf. In the case of Mr. Pfungst the horse gave the unusually high number of fifty taps. The attention of the observer had been taxed too long and had failed him (two seconds is the most favorable time). The head-jerk of Mr. von Osten evidently occurred during a lapse in Mr. Pfungst's attention and therefore remained unnoticed.

-----------------+----------+----------+----------+----------
| v. H. | Pf. | Schu. | St.
-----------------+----------+----------+----------+----------
Questioner. | I II | I II | I II | I II
-----------------+----------+----------+----------+----------
R. | 44% 60% | 62% 88% | -- -- | 0% 48%
V. Osten. | | | |
W. | 56% 20% | 12% 0% | -- -- |100% 22%
-----------------+----------+----------+----------+----------
R. |100% 92% | -- -- | -- -- |100% --
Pfungst. | | | |
W. | 0% 0% | -- -- | -- -- | 0% --
-----------------+----------+----------+----------+----------
R. | -- -- | 74% 100% | 83% 100% | -- --
Schillings. | | | |
W. | -- -- | 5% 0% | 17% 0% | -- --
-----------------+----------+----------+----------+----------

The results of the experiments are given in the second table. The general arrangement corresponds to that of the first table. Even though the absolute number of tests was small, yet for the sake of giving a better general view, all values are given in percentages. The tests in which the movement of the questioner had preceded that of the horse--as had been anticipated--are recorded under "R" (right); under "W" (wrong), we have recorded those cases in which the testimony of the stop-watches--contrary to our expectation--indicated that the reverse order prevailed. Finally, those cases which would complete the 100%, i. e. those in which the watches indicate simultaneity of the movements in question, are not recorded.

From this table we may note the following: The time-measurements for Mr. Schillings and Mr. Pfungst are quite in agreement and go to show that the order in time of the head movement of the questioner and the back-step of the horse was exactly what had been expected. The few contradictory cases which occur in Series I of the observations upon Mr. Schillings are to be accounted for by the fact that he was here for the first time the subject of observation, whereas the recorded time-measurements in the case of Mr. Pfungst had been preceded by a number of practice tests. The results of the measurements taken in the case of Mr. von Osten were far less satisfactory. Even if one were to allow a series containing barely more than 50% of "right" cases as sufficient proof of the correctness of our expectation regarding the order of the movements of the questioner and the horse, only three of the six series obtained with Mr. von Osten as subject, would satisfy this expectation. However, since four of the six series show a greater number of cases of simultaneity (their percentage may be easily deduced by referring to the per cent of "right" and "wrong" cases), the proposed method would give a distorted view, and therefore it appears that the more correct method would be to consider simply the numerical ratio of the "right" and "wrong" cases. Since, furthermore, Series II shows, in every case, a decided change which is similar for all observers (note especially Pfungst), there can be no doubt but that practice is here involved, and that Series II is to be regarded as the true standard. Throughout this series we find a preponderance of "right" cases. Therefore, the table unmistakably confirms the expected order in time. That there were more "wrong" cases with Mr. von Osten as subject than with the other questioners is to be explained by the fact that the decisive movements were far less easily observed in this case, than in that of the other questioners. (See page 49.) We expect that Series III would show the same results, or approximately the same results in the case of Mr. von Osten that it did for Mr. Pfungst and Mr. Schillings, but unfortunately he declined to act as subject. In the meantime, however, new and decisive proof presented itself which destroyed all possible doubt.

Before adverting to it, let us consider in a few words the reaction-time of the horse,--the time elapsing between the final sign of the questioner and the reaction of the horse (i. e., the back-step). Unfortunately this time cannot be directly determined. All that can be ascertained from our time-measurements, is the time intervening between the moment of the head-jerk and the moment in which the reaction of the horse is noted. (See page 51). This time averaged, for the 127 measurements, .45 seconds. If we stated the unavoidable error, (obtained on the basis of extended supplementary measurements which it is not necessary to consider here) as .15 seconds, and apply it to the value found above, we obtain .3 seconds as the probable reaction-time of the horse.[K]

[Footnote K: See page 126 on the corresponding reaction-time in the
case of man. Similar tests have been made in the case of animals in
only one instance, and that for dogs, by E. W. Weyer.[5] But, as
might have been expected, they did not yield any satisfactory
results.]

That the tapping--as well as all other movements of the horse--was nothing other than a reaction upon certain visual stimuli, was proved beyond a doubt by the fact that the voluntary execution of the head-jerk and of other movements--which we will describe in more detail later on,--brought about all the proper responses on the part of the horse. Thus, artificial synthesis became the test of the correctness of analytical observation.

To elucidate; if the questioner retained the erect position he elicited no response from the horse, say what he would. If, however, he stooped over slightly, Hans would immediately begin to tap, whether or not he had been asked a question. It seems almost ridiculous that this should never have been noticed before, but it is easily understood, for as soon as the questioner gave the problem he bent forward--be it ever so slightly--in order to observe the horse's foot the more closely, for the foot was the horse's organ of speech. Hans would invariably begin to tap when I stooped to jot down some note I wished to make. Even to lower the head a little was sufficient to elicit a response, even though the body itself might remain completely erect. Of thirty tests made in this position, twenty-nine were successful. Hans would continue to tap until the questioner again resumed a completely erect posture. If, for instance, I stooped forward after having told the horse to tap 13, and if I purposely remained in this position until I had counted 20, he would, without any hesitation, tap 20. If I asked him to add 3 and 4, but did not move until 14 was reached, he would tap 14. Twenty-six such tests gave similar results.

The reaction of the horse upon such a signal for stopping showed slight modifications according to the time which elapsed between the last tap and the signal for stopping. These modifications, which had hitherto been paraded as expressions of the horse's psychical power may be illustrated by the following schematic figures (Figures 1-4). In all of them the dotted line _c-d_ represents the ground level; _d_ shows where the horse's right forefoot was located before he began tapping; _a_ and _c_, respectively, indicate the place to which the foot is lowered during the process of tapping. The unbroken line gives the direction of the back-step.

If Hans, having raised his foot from _a_ to _b_--preparatory to tapping,--receives the signal at or just before the moment he lowers the foot, he immediately swings it in a wide circle from _c_ back to its original position at _d_, (Fig. 1). As a matter of fact _a_ and _c_ coincide, but are juxtaposed in the diagram for the sake of schematic utility. This was the usual form of the back-step.

If the signal for stopping is given a little after the last tap (Fig. 2), i. e., at the time that the foot is already being raised for another tap, then the back-step occurs as _a-b-d_. The horse thus gives, at the moment it receives the signal for stopping, a changed impulse to the moving foot. The curve, therefore, has a kink at _b_, and the back-step occurs with seeming hesitancy,--Hans appears not quite certain of his result.

If the signal be given somewhat later still (Fig. 3), i. e., when the foot is being lowered to complete a tap, Hans is still able to put on the brakes--as it were--and draw back his foot before it reaches the ground. The whole process gives the impression that the horse was just about to make a "mistake" of one unit, but at the last moment had bethought himself of the correct answer.

Finally, if the signal be deferred still longer, it becomes impossible to prevent the extra tap. The back-step again has the same form as in figure 1; Hans has made a "mistake" in his answer by one unit too many.

Conversely, if the head-jerk of the questioner occurs too soon; i. e., at the moment the horse has raised his foot for the final tap to the height _b_, (Fig. 4), then the tap is not completed,--but the foot, without touching the ground, makes the curve _b c_{2} d_, back to its original position. Hans has again made a "mistake" in his answer,--this time by one unit too few.

All these variations go to show one thing: Hans never knows in advance which tap is to be the final one. These variations in his reactions occurred often without having been intended by the questioner. But to bring them about at will required skill, on account of the shortness of the time involved in the reaction.