EXPLANATION OF THE OBSERVATIONS
The author having described the observations made upon the horse, and
having discussed the activities of the questioner upon the basis of
observations made objectively and upon his own introspections, and
having verified the results thus obtained, by means of laboratory
tests,--we are now in a position to solve satisfactorily all the
problems which this interesting case has presented.
That which is least difficult to understand is the horse's seeming
knowledge of language and particularly his ability to answer questions,
no matter by whom, or in what dialect, they were put. As a matter of
fact, it made no difference who desired an answer, for the only person
upon whom the experiment depended was the questioner, that is, the one
who asked the horse to tap. We have everywhere designated this person as
the experimenter or questioner. It was he who gave the directions, and
since all that were involved were visual signs, the drama in which Hans
appeared as the hero, was nothing but a pantomime. All speech was
superfluous and, except in so far as the tone of voice in which it was
spoken was soothing or reprimanding, it was quite unintelligible to the
horse.
From the foregoing, the reader understands without further explanation
Hans's ability to count and to make computations. If the number of taps
had depended solely upon the length of time and the angle at which the
questioner bent forward, the horse would have been able to tap any
number desired. Since, however, only the right foot was employed, the
left one being used at most for making a final tap, the number of taps
had an upper limit which was due to the fatigue of the animal. This
limit was about 100. That it was possible to ask such questions as: "How
many times is 100,000 contained in 654321?", and thus to give problems
involving millions, is perfectly clear.
All wonderful feats of counting and computation which were accomplished
while thus experimenting with the horse are to be accredited, not to the
horse, but to the questioner. If such is the case, they certainly cannot
be considered astonishing. Thus, when to the question, "How many of the
gentlemen present are wearing straw hats?" the horse answers correctly
in accordance with the wording of the question and omits the straw hat
of a lady, then Mr. von Osten is the guide. It is no wonder that Hans
never showed the slightest excitement when confronted with difficult
problems, nor that it apparently took no time whatever to solve them.
Hans, however, was also a faithful mirror of all the errors of the
questioner. Aside from mistakes due to occasional interruptions on the
part of visitors, these errors had two sources: faulty computation and
inadequate concentration--i. e., aside from arithmetical errors on the
part of the questioner, were his premature or belated movements. Since
both of these factors might be operative, the following three
possibilities arise.
(_a_) The questioner computes correctly but does not move at the proper
moment. Nearly all the errors which had been accredited to the horse,
were of this kind.
A part of these errors had the appearance of being significant, that
is, they might be interpreted as a misapprehension of the question. If,
for instance, instead of a sum only one of the quantities was given, or,
if instead of a product only one of the factors was given, it might be
interpreted that the horse simply wished to repeat the problem. Thus,
Mr. von Osten in response to the question: "How much is 3 times 5?",
twice in succession received the answer, "3", and upon my question, "How
much is 3 plus 4?" he answered, "3", and to "How much is 2 times 6?" he
tapped 6, and to "What is one-fourth of 36?" 4. In part (certainly in
the second and third example cited) an individual quantity or factor had
been emphasized in the consciousness of the questioner (cf. page 105)
and in part the reactions were due to chance. Thus, when Mr. Hahn asked
the question: "What is one-half of 10?", he received the following
responses: 2 and 10, and then 17 and 3. To this class belong also, the
tests made by the Commission of September and reported in Supplement
III. (See page 255).
Other errors, even though they may not have appeared to be significant,
might yet have been characterized as mistakes due to speed; as when, e.
g., Hans made an error of one unit--and sometimes, though less
frequently, of two units--too much or too little in his response. One
might be led to believe that Hans had not made an error of calculation
but merely of counting in the process of giving his result, which always
had to be done by the cumbersome method of tapping. As a matter of fact,
the trouble lay in the wrong degree of concentration on the part of the
questioner: In errors of +1, tension was too slight, in those of -1, it
was too great (see page 91). This comes out clearly in a comparison of
the two more extensive series which I took in the case of Mr.
Schillings. During the first series, he was well disposed, and was able
to concentrate effectively, while during the second, he was nervous and
easily diverted. This difference in intensity of concentration in the
case of the two series is attested, not only subjectively by Mr.
Schillings's introspective statement, but may be measured objectively by
means of the number of final taps which the horse gave with his left
foot during these two series. We saw (page 94) that these final taps
were always a sign of intense concentration and, as a matter of fact,
one-half of the horse's responses to Mr. Schillings during the first
series were made in this way; whereas, in the second series, only
one-third were of this sort. (I, myself, was never able to get, without
conscious control, a greater number of this type of response.) We may
therefore say that, in the first series we had a high degree of tension,
or concentration, whereas, in the second series, we had a low degree.
The errors distribute themselves over the two series as follows:
+1 +2 -1 -2
Series I (31 tests)
Correct responses: 87%
Incorrect " : 0% 0% 13% 0%
Series II (40 tests)
Correct responses: 40%.
Incorrect " : 40% 8% 2.5% 0% (and 9.5%
other kinds of errors.)
We find in Series I no "+1" errors, but only "-1" errors; in series II,
on the other hand, the errors are almost exclusively of the "+1"
category, equaling the number of correct responses, and there is only
one "-1" error. A series obtained in the case of Mr. von Osten is almost
as satisfactory an illustration. When he first began to take part in
tests in which the procedure was the one we characterized as "without
knowledge" and had to note their complete failure, he was thrown into
such confusion that the responses in the case of procedure with
knowledge were also incorrect. The errors there were always +1, (whereas
those in the case of procedure with knowledge, which were due to quite
different causes, were very great and inconstant.) The number of +1
errors obtained on this occasion comprises one-fourth of all the plus
errors which were ever obtained in the case of Mr. von Osten during the
entire course of these experiments. Finally, I would mention two
examples of my own. In the course of my very first attempts with Hans I
obtained, as I said on page 89, three responses in a total of five which
exceeded the correct result by 1. This I would explain by the fact that
although I employed a high degree of concentration, I nevertheless was
somewhat skeptical. The result was a certain deficiency in the degree of
concentration. A second example which I would cite is taken from the
period in which I had already discovered the cue to Hans's reactions and
goes to show that I was then still able to eliminate the influence of
this knowledge and to work ingenuously. To the question, "How much is 9
less 1?" I, momentarily indisposed, received the answer 10, and then six
times in succession the answer "9", and finally the correct response,
"8".
Errors of another kind--the not infrequent offenses against the very
elements of counting and the fundamental arithmetical processes--were
regarded in part as intentional jokes and by an authority in pedagogy as
a "sign of independence and stubbornness which might also be called
humor". Hans emphatically asserted that 2+2 was 3 or he would answer
questions given in immediate succession as follows: "How many eyes have
you?"--2. "How many ears?"--2. "How many tails?"--2. These errors, as a
matter of fact, evince neither wit nor humor, but prove incontrovertibly
that Hans had not even mastered the fundamentals.
Many of the errors baffle every charitable attempt at interpretation.
These gave the horse the reputation of capriciousness and unreliability.
If Hans designated the tone "e" as the seventeenth, or "g" as the
eleventh, or when he called Friday the 35th day of the week or believed
50 pfennige to be worth only 48, the cause for these responses lay
either in the insufficient degree of tension on the part of the
questioner (as in the first three examples) or in the extravagant
expenditure of the same (as in the last case). If, therefore, the horse
at times would "hopelessly flounder" which would seem to be indicated by
tapping now with the right and now with the left foot, then as a matter
of fact, this form of reaction came about as was described on page 61,
with this difference that there we had to do with voluntary controlled
movements on the part of the questioner, whereas here, they are the
result of an unsuitable degree of tension which expressed itself in
frequent and disconcerting jerks. Besides the answer 3, this so-called
floundering was the only reaction the average person could obtain from
the horse in the absence of Mr. von Osten and Mr. Schillings. It would
however occur also in the case of these gentlemen and would be received
by them with resentment when in truth it was Hans's greatest feat, for
he showed his extremely keen reaction upon every movement of the
questioner. To this group belong also the errors in the case of higher
numbers, the sole cause of which lay in the difficulty with which
tension could be maintained and the body kept motionless for so long a
period. These errors occurred in accordance with a certain law. If, for
instance, a certain test repeatedly evoked incorrect responses, the
questioner would gradually increase the duration of tension and would
thus come a little nearer to the desired goal with every test. In this
way, Mr. von Osten desiring 30 as an answer obtained consecutively the
responses, 25, 28, 30; and I, myself, for the answer 20, received
consecutively the responses 10, 18, 20 (see also the laboratory tests,
page 105). Sometimes too, the questioner would flag in his efforts
before the goal was reached. Thus in one of my first tests, I received
for the answer 11 the following responses: 1, 4, 5, 7, 4. I was unable
to get beyond 7. In other instances, the horse responded first with too
few and then with too many taps. The correct response therefore could
only be obtained after an appreciable amount of gauging of tension, as
in target practice there must be a gauging of distance. (See page 92).
In this way Mr. von Osten obtained for 10 the responses 8, 8, 11, 10,
and Mr. Schillings for 17, received 9, 16, 19, 18, 18, 14, 9, 9, and
finally, after some efforts, 17 taps. Thus there was a rise from 9 to
19, then a fall back to 9 and after eight tests the correct response. As
long as we attempt to explain this fact as error on the part of the
horse, so long will it remain inexplicable, but the moment we regard it
from the point of view of the psychology of the tension of expectation,
it becomes perfectly plain.
The same holds true for the curious predilection which Hans appeared to
have for the numbers from 2 to 4, especially for 3 (see page 68). As a
matter of fact the cause of this lies in nothing other than the
inadequate concentration of attention on the part of the questioner and
less often in an extravagant expenditure of concentration, which
explodes immediately after the first tap on the part of Hans (as in the
case of my first tests); but usually the cause lay in a complete lack of
concentration, though the same result may be produced by various causes.
It is usually after 2 to 4 taps of the horse's foot that the questioner,
who does not concentrate, makes his first move which naturally puts an
end to the tapping on the part of the horse. As a rule this jerk follows
immediately upon the second tap. (On the other hand, relaxation of
attention is very difficult upon the first tap. See page 95). The
questioner, however, would expect further tapping and therefore would
not bring his body back to a completely erect position and the result
would be a 3, the last unit of which would be given by the final tap
with the left foot. Here we also obtained light as to the answers which
Hans gave in those tests in which the method was that of "procedure
without knowledge". These responses had nothing to do with the problem,
for neither the horse nor any one else knew the solution. But in the
horse's responses the degree of tension of the questioner's
concentration was faithfully mirrored. An experimenter who was as
skillful in concentrating as Mr. von Osten, obtained--almost without
exception--very high numbers, whereas one whose concentration was slight
would receive in response to nearly all questions the answers 2, 3 or 4.
Thus, the Count zu Castell received in response to seventeen questions
the answer 2, three times, the answer 3, six times, and the answer 4,
four times, two answers being accidentally correct.
Another group of errors was characterized as stubbornness on the part of
Hans, such as his persistence in repeating an incorrect response, or his
repetition of a former correct answer in response to later questions
where it was perfectly senseless. During a demonstration before a large
number of persons, I held a slate with the number 13 upon it within the
horse's view and also within view of the spectators. I, myself, did not
know what number was written on the slate. Having been asked to tap the
number, Hans responded by tapping 5. The grand-stand shouted "Wrong!" I
asked Hans to try again. Four times in succession he answered 5. At
another time Mr. von Osten and I each whispered a number (7 and 1,
respectively,) into the horse's ear and asked him to add the two. Three
times in succession he tapped 11. After the test had been repeated in
accordance with "procedure with knowledge" and a correct response had
been received, we tried once more a test of "procedure without
knowledge". Again, he responded with an 11. On a third occasion, I asked
Hans to tap 5. He responded with a 4 and then, correctly, with a 5.
Thereupon, I asked him to tap 6. Again, he responded with a 4. Then I
asked him to tap 7. Once more he responded with a 4, and only when I
proceeded to count aloud did he tap 7 correctly. I had him repeat the 7
and then went over to 9. Promptly he responded with another 7. In these
cases, which by-the-way were not very frequent, we have to do, not with
stubbornness on the part of Hans, but with the persistence of that
number in the consciousness of the questioner. Modern psychology has
recognized this tendency of ideas, which have once been in
consciousness, to reappear on other occasions even though they are
wholly inappropriate. It has been termed "perseverative tendency."
(Perseverationstendenz).[21]
While the errors thus far discussed appeared sporadically in long series
of correct responses, there still might be observed at times a massing
of errors, usually at the beginning of a day of experimentation or at
the beginning of a new series. We were regularly told that Hans always
had to have time to adjust himself to new circumstances. The records
often showed comments such as these: "After a number of practice tests
the horse appears particularly well disposed", or "Hans, at first
inattentive, does not respond. Suddenly he gets the hang of things".
Different questioners who worked with the horse required different
lengths of time to obtain proper responses. Some needed a quarter of an
hour, others scarcely half a minute. I, myself, found that in the degree
in which I learned to control my attention, in that degree did this
phenomenon tend to disappear, but would reappear the moment I became
indisposed. From this we see that, instead of attributing all sorts of
mental characteristics, such as stubbornness, etc., to the horse, we
should lay them to the account of the questioner. As a matter of fact we
find that this "getting into the sweep of things", i. e. the overcoming
of psycho-physical inertia, has long been known in the case of man and
has been experimentally determined and called "Anregung" (excitation) by
the psychiatrist, Kraepelin,[22] and his pupil, Amberg.[23] A massing of
errors toward the end of a long series occurred only when the questioner
was fatigued. There was nothing which had to be interpreted as fatigue
or as indisposition on the part of the horse, (except in the few cases
of very large numbers, cf. page 67). To be sure, Mr. von Osten always
offered these two excuses. That they were without warrant is shown by
the fact that Hans, after appearing indisposed or fatigued while working
with one questioner, would nevertheless react promptly and correctly a
moment later for some other experimenter, and furthermore, when working
with me, the number of his correct responses would rise or fall with my
own mental disposition.
Finally, I would here note a rather interesting observation for which I
am indebted to Mr. Schillings and the Count zu Castell. They had
noticed, independently of each other, that the horse would often fail to
react when for any length of time he was given problems dealing with
abstract numbers, even though they were of the simplest kind; but that
he would immediately improve whenever the questions had to do with
concrete objects. They believed that Hans found applied mathematics more
interesting, and that abstract problems, or those which were altogether
too elementary, bored him. The Count zu Castell furthermore noticed that
the responses tended to be more correct as soon as he had the horse
count objects which he, himself, (Castell) could see during the test.
Quite in accord with this is the statement to be found in the report of
the September-Commission, in which we find this note in a discussion of
the arithmetical problems (not involving visible objects), which the
gentlemen already mentioned had given the horse. "The horse responded
with less and less attentiveness and appeared to play with the
questioner." Here again, that was looked for in the animal which should
have been sought in the man. Mr. Schillings was capable of intense, but
not continued concentration and it was he who was bored, and not the
horse. And it was the Count zu Castell and not the horse that found it
necessary to invoke the aid of perceptual objects to bring his
attention to the proper height of concentration.
The reader will see that thus far I have supposed the horse to be a
never-failing mechanism and that I have placed all errors to the account
of the questioner. The horse never failed to note the signal for
stopping and therefore never was the immediate cause of an error. It is
not to be denied that now and then he would cease tapping spontaneously
and in this way would become the cause of an error. We have no data on
this point, but undoubtedly the horse's share in the total number of
errors was very slight.
(_b._) Another source of error was faulty computation on the part of the
questioner. The questioner made the signal for stopping when the
expected number of taps had been reached. The horse faithfully mirrored
the miscalculation of the questioner. I have knowledge of only one such
case. The journals report that once Mr. von Osten, when someone called
to his attention that Hans had indicated the wrong day of the week,
replied: "Yes, you are right, it was not Thursday, but Friday,"
whereupon Hans being asked again, promptly responded correctly. This
appeared to the reporter in question as proof of the subjective
influence of Mr. von Osten upon the horse.
(_c._) When errors in calculation and failures in proper concentration
combine, i. e. when the questioner makes a mistake in calculation
because he is excited or inattentive and for the same reason does not
make the movement, which is the signal for stopping, in accordance with
the number which he deems to be the correct answer, then the result is
usually wrong, but it may be correct in the few cases in which the two
errors exactly compensate each other. Nothing has been so effective in
establishing Hans's reputation, nothing has brought him so many
followers, as these cases in which he, rather than his mentor, has been
in the right. Compared with the mass of cases in which Hans was wrong
these latter cases are diminishingly few in number, yet these few made
such an impression upon the observers that their number tended to be
overestimated. As a matter of fact, I have been able to discover records
of only seven such cases. Two of these were reported by the Count zu
Castell. On the 8th of September, he entered the horse's stall, alone,
and believing it to be the seventh day of the month, he asked Hans the
date. The horse responded correctly with 8 taps. At another time he held
up before Hans a slate on which were written the numbers 5, 8 and 3 and
asked the horse to indicate their sum which in the momentary excitement,
vaguely appeared to Castell to be 10. To his chagrin he noticed that
Hans continued to tap. Thereupon he intentionally remained motionless
until the horse had stopped tapping spontaneously--as he thought--at 16.
(The newspapers reported that the numbers to be added had been 5, 3, and
2; that the questioner had expected the answer 11, but that Hans had in
three tests always ceased tapping at 10.) In both cases the questioner
regarded the answers of the horse as wrong and recognized his mistake
when his attention was called to it. I, myself, had the same experience.
One time I received in response to the question, "What day of the week
is Monday?", the answer 2, although I had expected the answer 1; at
another time I asked, "How much is 16 less 9?", and the horse responded
with 7 taps, although I had erroneously expected 5. I noticed my mistake
only when my attention was called to it by one of those present. Another
example is related by Mr. Schillings. A row of colored cloths lay
before Hans. Beside them stood an army officer. Pointing to the latter's
red coat Mr. Schillings asked the horse to indicate, by means of
tapping, the place in the row where a piece of the same color lay. Hans
tapped eight times, but Mr. Schillings reprimanded him because the red
piece was, as a matter of fact, second in the row. Upon a repetition of
the test, Hans again tapped 8. (By some, the facts are recounted as
having been the other way round; viz.: Hans tapped 2 instead of 8. This
of course would call for a different explanation.) It was noticed that
at the place which would be indicated by eight taps there was not a red
piece but a carmine colored piece of cloth. A newspaper reports,
somewhat vaguely, a sixth case as follows: Hans was asked to spell the
name "Doenhoff" and began correctly: "Doe". Mr. von Osten, who somehow
began to think of another name, "Dohna", interrupted him and wished to
correct him by suggesting o instead of oe (i. e., 2 taps instead of 3).
Hans, however, continued to spell the entire word with the greatest
equanimity. He had not erred. A similar experience is reported by Mr. H.
von Tepper-Laski, the well known hippologist. Although the details have
slipped from his memory, he reports that in the case in question the
correct answer was thrice refused by the questioner who thought that the
horse's answer was incorrect. Hans, upon being severely reprimanded in a
loud and harsh tone of voice, turned about as if disgusted with the
injustice of the man and made straight for his stall.--It is clear that
in the cases described we are not dealing with accidentally correct
responses, for in nearly every case the test was repeated a number of
times and the same responses were received each time. As a matter of
fact, my own introspection convinced me that the third and fourth cases
were surely, and the first and sixth were very probably, due to
insufficient concentration on the part of the questioner. Accordingly
there is everywhere in these cases a difference of +1 or +2 between the
number thought of and the number tapped (see page 92 f.). The data in
the second and fifth and still more in the seventh case were too meager
to warrant an attempt at explanation, for it is not even known whether
Hans responded with more or fewer taps than was expected by the
questioner. It is unfortunate that a more complete record was not made.
The frequent and intentional attempts of Mr. von Osten to induce the
horse to give an incorrect response,--which, by-the-way, were regularly
unsuccessful--belong only apparently to this group. Thus he asked, e.
g., "2 times 2 is 5, is it not?" "3 times 3 is 8?", etc., but Hans
refused to be misled, and responded correctly. This was from the very
beginning one of the main arguments for independent thinking on the part
of the horse. The actual procedure was as follows, even though the
questioner had said "2 times 2 is 5", there still was present in his
consciousness the number 4. I, myself, would think either of the first
member of the equation, i. e., 2 times 2, in which case Hans would
respond with 4 taps or I would have in mind the second member, i. e., 5,
in which case he would respond with 5 taps. Never did I succeed in
thinking of both at the same time. The association between the thought
"2 times 2" and the concept "4" is so close and supported by so many
other associations that the attempt to form a new one, that is at
complete variance with all these, is futile. One may say "2 times 2
equals 5" but it is impossible to conceive it.
Let us turn now, from the tests in counting and computation to those in
reading. We have seen that Hans manifested his seeming knowledge of
language symbols in a threefold manner: he might approach a slate on
which was written the symbol asked for, or he would indicate its
location in a series of slates by means of tapping, or finally by means
of so-called spelling of the word which was written upon a slate or
placard. The responses by means of approaching a placard were very often
unsuccessful, while indications by means of tapping were scarcely ever
unsuccessful. If it were true that higher intellectual processes[T] were
here involved, then the converse would have been expected, for tapping
required not only the ability to read, but also the ability to count.
If, on the other hand, we assume that the horse simply followed the
directions given by the questioner's movements, this seeming difficulty
resolves itself, for it would be more difficult for Hans to perceive the
signs which he receives while moving than those which he receives while
tapping. When we recall that it was easier to direct the horse to a
placard near the end of a row than one nearer the center (see page 81),
we can readily understand how it was that during the experimentation
carried on by the September-Commission (Supplement III; page 255), Hans
was able to point out immediately the placards on which were written the
names "Castell" and "Stumpf", for they were at the two extreme ends, but
was unsuccessful in locating the one on which was written the name
"Miessner" which was not a bit more difficult to read, but was located
at the fourth place in the row. He first approached the fifth card, then
upon repetition of the test he pointed out the other neighboring tablet,
viz., the third.
[Footnote T: Professor Shaler[24], a well-known American savant,
mentions a three-year old pig belonging to a Virginian farmer, that
was able to read and had some understanding of language. From
numerals which were written upon cards and spread out before it,
this pig could compose dates. It could also select from among
certain cards one upon which was written a given name, asked for by
the master. Supposedly no signs of any kind were given. (Shaler
thought to exclude effectively the sense of smell, which is so
highly developed in the pig, in that he, Shaler, himself smelled at
the cards, since he also "possessed an acute olfactory sense!")
Since we are told that the farmer in question made a business of
supplying trained pigs for exhibition purposes, the case appears
suspicious. We hear of a pig exhibited in London, that was able to
read and spell, and could also tell the time by the watch[25]. We
cannot tell, however, whether the two pigs, which beyond a doubt
were mechanically trained to respond to signals, are identical or
not.]
In spelling, Hans was quite indifferent whether his table with the
eighty-four number signs upon it stood before him, for he had no
knowledge of letters. Neither Mr. von Osten nor Mr. Schillings required
it, for the former knew the table by heart and Mr. Schillings told me
that before every test he made a note of the numbers which were
necessary to indicate the required letters, trusting in this way to
control the responses of the horse and never guessing that by so doing
he was making it possible for the horse to answer correctly. The
newspaper reports aroused much interest at the time by stating that Hans
was able to spell such proper names as "Plueskow" and "Bethmann-Hollweg",
even to putting in the difficult "w" and "th". The friends of Mr. von
Osten at the same time called attention to the exquisite auditory
acuteness of the horse which enabled him to perceive the aspirated "w"
and to discriminate between the "th" and "t", (the "th" is softer than
the "t" in German.--_Translator_). This explanation, of course, must
have appeared somewhat daring even at that time.
Hans was quite guiltless of the many limitations imputed to him
concerning his knowledge of symbols. That he was unable to read capitals
or Latin script was merely a vagary of the master, like the belief that
it was necessary to confine one's self in one's questions to a certain
vocabulary and to a certain form. Mr. von Osten's apparent failure to
elicit responses from the horse on topics of which it was ignorant is a
beautiful illustration of the power of imagination. Mr. von Osten was
convinced from the very first that Hans could not answer such questions.
When the belief in success was lacking, of course there was not the
requisite amount of concentration which, alone, leads to perceptible
expressive movements and thus elicits a successful reaction on the part
of the horse.
Mr. Schillings, owing to his great impressionability, remained long
under the spell of Mr. von Osten's point of view. Thus I find in the
record of the September-Commission that the question "How much is 3 plus
2?" was answered incorrectly by Hans, but he responded correctly the
moment Mr. Schillings replaced the word "plus" which was "tabooed", by
the word "and". For a long time also he could receive no response to
questions put in French until one day he made the discovery that,
curiously enough, the animal never responded adequately unless he
himself firmly believed in the possibility of success. It is noteworthy
that the Count zu Castell, independently of Mr. Schillings, made the
same discovery. Mr. Schillings made his curious discovery--which he was
unable to interpret, but which aroused some suspicion--on the following
occasion. One day--whether accidentally or because his prejudice was
temporarily overcome--he commanded; "Dis deux!". Hans responded promptly
with 2 taps. He was greatly surprised and believed that Hans had gotten
hold of the French by hearing it spoken in his environment. Possibly he
understood also "trois" and "quatre"? He put the questions and received
correct responses. He asked again, "dix", "vingt", and so on to
"soixante". At "soixante-six" he became doubtful. Indeed, Hans failed
him. At "quatre-vingt", the game began again. "Cent", again, succeeded.
The old saying that "Faith will move mountains" was verified once
more.[U]
[Footnote U: It has been scientifically proven that a number of
supposed mystical phenomena, table-moving, table-rapping, and
divination by means of the rod, all are the result of involuntary
movements made unawares by those concerned, just as in the case of
this work with Hans. (We must of course except those not infrequent
instances in which the phenomena in question are purposely and
fraudulently simulated.) There is this difference, however, that
there the thing affected is a lifeless object,--the table or the
rod,--here it is a living organism, the horse; hence there the
immediate effect of the movement is physical work in the form of
energy expended in moving the table, here the movement becomes a
visual stimulus. A number of observations which I find in the
relevant literature, and which I shall introduce into this chapter,
may serve to show how close is the similarity between the two cases,
how much depends upon the questioner, and how little really upon the
instrument--whether table or horse--which is acted upon.
Two examples will suffice to illustrate the significance of belief
and of the concentrated attention that results from it. The first is
taken from the letters of Father P. Lebrun on the divining rod[26],
which appeared in 1696. An old woman once told a treasure-seeker
that she had always heard that a treasure was buried at a certain
place in the fields. The man, who was known as an expert in the art
of using the divining rod, immediately set out to locate the gold.
Lo, and behold, the moment he set foot on the spot described by the
old woman, the branch turns downward, and from its movements the man
gathers that twelve feet below ground there lies buried some copper,
silver and gold. He calls a peasant to dig a pit eleven feet deep,
then he sends him away so that no other should get into the secret.
He himself digs a foot deeper, but all in vain, for he finds
nothing. Standing in the pit, he again takes up the branch. Again it
moves, but this time it points upward, as if to indicate that the
treasure had disappeared from the earth. Dismayed, he climbs out of
the pit and questions the branch a third time. This time it points
downward once more. He climbs back into the pit. Presently he feels
the prick of conscience (for in the 17th century many regarded the
dipping of the divining rod as the work of the Devil). Terrified, he
exclaims: "O God, if the thing I am doing here is wrong, then I
renounce the Evil One and his rod (s'il y a du mal, je renonce au
demon et a la baguette)". Having spoken, he once more takes the rod
in hand to test it. It does not move. Horrified, for now there was
no longer any doubt that Satan was the cause of its movements, the
man makes the sign of the cross and runs away. But he had hardly
gone more than two or three hundred paces when the thought strikes
him: Is it really true that the branch will no longer move for him?
He throws a coin to the ground, cuts a branch from a bush nearby,
and is overjoyed when he notes how it dips down toward the money.
Another example is to be found in a report of the well-known
physicist, Ritter[27], of Munich, which appeared during the early
part of the 19th century. Ritter, a man with a bent for natural
philosophy and metaphysics, describes an instrument which was to
replace the divining rod, and which he called "balancier." It was
simple enough, consisting of a metal strip that was balanced
horizontally upon a pivot, and was supposed to be put into motion in
the presence of metals. Ritter used this instrument in his numerous
experiments with the Italian Campetti, a man who had achieved a
measure of fame in Europe for his ability to discover springs and
metals by the use of the divining rod. Carrying the "balancier" on
the tip of the middle finger of his left hand, Campetti--whose
integrity one cannot cavil at--had to touch repeatedly a plate of
zinc or pewter, and had to count aloud the number of touches he
made. The following curious law was found to obtain (that was
probably suggested to the subject by Ritter without his being aware
of it): with the first contact the "balancier" turns to the left,
with the second to the right, and with the third it remains at rest.
At 4 it turns once more to the left, at 5 to the right, at 6 it
remains at rest, etc. It remained immovable only at the so-called
trigonal numbers (3, 6, 9, 15, 21, etc.). Ritter tells us that when
Campetti did not really count or did not think of the number, then
it would not have any influence whatever upon the action of the
instrument. This Ritter ascribes to the agency of electricity (which
in the 18th and 19th centuries was made to play very much the same
role that Satan had played in the 16th and 17th centuries).
The similarity of these two cases and that of Mr. Schillings is
evident. When the questioner of the horse and the bearers of the
"balancier" and of the divining rod are confident of success, they
succeed. When they do not expect success, they fail.]
Hans's seeming knowledge of the value of coins and cards, of the
calendar and the time of day, as well as his ability to recognize
persons or their photographs, can now be readily understood. In all of
these cases, we had to deal, in so far as knowledge is concerned, only
with that of the questioner,--the horse simply tapped the number the
questioner had in mind. The meaning which was supposed to be expressed
by the tapping never existed as far as Hans was concerned; it was only
in the mind of the questioner that the concepts: ace, gold, Sunday,
January, were associated with "1", etc. The same was true with regard to
all other wonderful feats of memory. The sentence: "Bruecke und Weg sind
vom Feinde besetzt", (The road and the bridge are held by the enemy),
which was given to the horse one day and correctly repeated by him on
the following day, was not an answer elicited from the horse by means of
a question, but rather a system of automatic reactions which were
induced by certain involuntary movements of the questioner as stimuli.
Far from showing a wonderful memory in these feats--as is claimed for
him by the very non-critical compiler, Zell[28]--Hans, on the contrary,
has at his service a remarkably small number of associations. For,
besides possessing the powers of any ordinary horse, he recognizes only
a few meager visual signs. To be sure, we find in the literature a horse
that was said to have recognized 1500 signals,[29] but all proof is
lacking and the report is so meager that we cannot discover whether
these signs were auditory or visual.[V]
[Footnote V: The French investigators Vaschide and Rousseau make a
reference to this case, and mistakenly state the number of signals
as 1500 instead of 115[30]. Ettlinger[31] takes over this wrong
figure and makes the additional mistake of assuming that the
reference is to an original investigation made by the two
Frenchmen.]
Having thus disposed of all questions concerning the horse's apparent
feats of reason and memory, let us turn to those in the field of
sensation. We shall begin with vision. That Hans was unable to select
colored pieces of cloth merely upon the basis of color quality, without
reference to their order, was shown in Chapter II. It would, however, be
somewhat hasty to infer color-blindness from this fact, as did
Romanes[32] on the basis of similar unsucessful responses on the part of
a chimpanzee ("Sally" of the London Zooelogical Garden). It is much
easier to explain the failure of the horse than that of the monkey on
the basis of intellectual poverty, a poverty of associative activity. It
presumably can discriminate between the various colors, but it cannot
associate with these their names. The existence of chromatic vision in
the lower forms is by no means as unquestionable as is assumed by
popular thought. Even teleological considerations which are often
brought forward (especially that of the ornamental and protective
coloring of so many animals) can never do more than establish a certain
probability. For definite proof, we need data given by observation (we
have none in this case), or experimental evidence. Such evidence we
have, but it is insufficient in quantity and unfortunately most of it
was obtained under inadequate experimental conditions.[W] We know
nothing regarding chromatic vision in the horse, though we have often
had trained horses which apparently possessed color discrimination. The
earliest report of this kind I find in a work published in the year
1573.[36] Here we read that a number of Germans exhibited two horses in
Rome which could, upon request of their masters, point out those persons
among the spectators who were wearing stockings of any designated color.
The passage, "conoscevano i colori", (they recognized the colors,)
proves nothing and no one has ever heard, even in modern times, of a
horse that actually knew colors.
[Footnote W: All told, there are hardly more than half dozen
experimental investigations of the color-sense in mammals,--to speak
only of these. Three of them deserve especial mention. One, the work
of the American, Kinnaman,[33] on two Rhesus monkeys. Then a brief
but careful piece of work by Himstedt and Nagel.[34] These two
investigators were able to determine that their trained poodle could
distinguish red of any tone or shade from the other colors, and from
Professor Nagel I learned that later the tests were extended and the
same was shown to be true concerning the blue and the green. And
finally there is an investigation which hitherto has been known only
from a reference which Professor Dahl,[35] the investigator, himself
makes. The work is on a monkey, Cercopithecus (Chlorocebus)
griseoviridis Desm. (Professor Dahl has kindly allowed me to look
over the records of the experiments. He intends to publish the
monograph at an early date.)
All of these investigators arrive at the conclusion that the animals
tested by them possess color-sense. The monkey last-mentioned shows
one peculiarity: it was unable to distinguish a saturated blue from
the black. It will require further tests to clear this up.]
Nor did Hans possess anything like that high degree of visual acuity
which had been attributed to him. He was supposed to be able to read
easily at a distance small, almost illegible script, which we ourselves
could decipher only with the greatest difficulty close at hand. It was
also supposed that he could distinguish ten-and fifty-pfennig pieces
whose faces had become worn beyond recognition for us. None of these
accomplishments have stood the test. We have no reason to believe that
Hans can see the objects about him more clearly than other horses,
regarding whom one usually assumes that they receive only vague visual
impressions. Horses do not as a rule seem to be near-sighted as is often
asserted by the layman, but rather somewhat far-sighted, or if we may
believe Riegel,[37] who tested some six hundred horses, they probably
have normal vision. But we are told that many horses--and according to
some authors all--have an innate imperfection which detracts
considerably from the clarity of vision. This imperfection consists in
an irregular formation of the sclerotic coat and of the lens of the
eye.[38] The two organs do not have the same refraction in all parts. As
a result, objective points are not imaged as points upon the retina.
(Hence the name: astigmatism, i. e., "without points", for this
disorder.) The retinal image of the object is not only vague, but also
distorted.[X]
[Footnote X: There is no justification for the wide-spread belief
that the horse which on account of the greater size of his eye (more
correctly, on account of the greater focal distance) receives larger
retinal images of objects than does the human eye, for that reason
also sees objects, larger than we do. Horses' shying is often
explained in this way. But the conclusion just mentioned is
erroneous. The retinal image is not the perceptual image. It
undergoes many transformations within the nervous system itself.]
Many will doubt whether with such imperfect images an animal can react
to directives so minute, as we have asserted to be true in the case of
Hans. In considering this question we must distinguish between the
directives for pointing out colors and the directives for tapping and
for head movements on the part of the horse. In pointing out and
bringing forth pieces of colored cloth there is involved the perception
of an object at rest, viz.: the direction of the questioner who is
standing quietly; whereas in the case of responses by means of tapping
the stimulus is the horse's perception of the questioner's movements.
Now, the construction of the horse's eye, as described above, is not
favorable for the perception of objects (so-called acuity of vision).
This may partly account for the slight success of the horse in those
tests in which he was required to select a piece of cloth of a
designated color, in so far as these commands were not accompanied by
calls or exhortations. Where human observers averaged eighty per cent
correct responses (page 135), Hans, under similar conditions was
successful in only one-third of the tests. In his errors he was also
wider of the mark than were the human observers (page 82). The object
perceived, to be sure, is a large one, viz.: the questioner, and he at
close range. We must therefore consider more specifically what are the
determining factors that make for success or failure of the response.
First of all, the innocent questioner very often did not designate the
direction with sufficient clearness. Furthermore, Hans presumably was
not able to discriminate sufficiently between the direction of the
experimenter's eye and that of his head, which two directions did not
always coincide. Finally the horse's attention was often diverted, while
he was running toward the piece indicated, by the other pieces lying to
the right and to the left, and for this reason the addition of a single
piece to the otherwise unchanged row of five pieces tended to decrease
greatly the chances of success.
The case is different with the perception of the directive signs for
tapping, for nodding and shaking the head, etc., all of which require
the perception of movements. This is not necessarily more difficult on
account of the imperfect constitution of the tissues that serve for the
refraction of light. Some authors even aver that this facilitates the
perception of moving objects. This view was first advanced by the
excellent ophthalmologist, R. Berlin[39] of Stuttgart. In arriving at
this view he was guided by the following considerations. The peculiar
form of astigmatism of the lens of the horse's eye, which Berlin has
described as "butzenscheibenfoermig",[Y] because it appears in the form
of a series of glossy concentric circles around the lens nucleus, has
the property of enlarging the pathway (and with it the rapidity) of
moving retinal images. If we take a speculum by means of which a view
may be had of the interior of the eye, and fixate a definite point on
the retina of the horse, and then make a slight movement of the head
horizontally, we find that the point fixated moves--apparently at
least--toward the border of the pupil. In a normally constructed eye
this seeming movement will be in a straight line, while in the eye of
the horse, (according to Berlin), its path is curved, and therefore
longer. Berlin believes that the same thing which here occurs in the
case of this merely apparent movement, must also happen when an external
moving object is imaged on the horse's retina. Its pathway, too, will be
curved, and therefore longer, so that if the head of Mr. von Osten moves
past the animal's eye, then the image on the horse's retina will take a
longer, more circuitous route than it would if the eye were not
astigmatic. We cannot, however, immediately conclude from the fact that
an objective movement is imaged as being greater in extent on the
retina, that it will therefore be more readily perceived by much less
that it will appear greater to, the horse, than would be the case if the
lens were normally constructed. The visual percept is not immediately
dependent upon the retinal processes, for between the two are
interpolated complex, inaccessible nervous processes. Still, Berlin
believes that he is justified in drawing this conclusion from a number
of relevant considerations. Accepting it, he believes that it would be
possible for the horse to perceive movements, that for the human eye,
which is not subject to this form of astigmatism, would lie below the
threshold.
[Footnote Y: "Butzenscheiben" are the small circular panes of green
glass, used in leaded windows in early days. They are high in the
middle (hence the name: "Butze," a protuberance) with a number of
concentric circles around the central elevation.--Translator.]
This theory, the simplicity of which certainly must make a strong
appeal, has been adopted by a number of well-known investigators
(Schleich[40], Koenigshoefer[41]). If we also could accept it, then Hans's
phenomenal power of perceiving the movements of objects would be
explained. But doubts arise which restrain us. Even if we were to accept
Berlin's view in general, we should still come upon the following
difficulties. In the first place, it is questionable whether the
peculiar form of astigmatism mentioned is indeed as common as he
supposes.[Z] The references in the literature are exceedingly meager on
this point. In order to make a few tests at least, I undertook to
examine nine horses with the aid of Dr. R. Simon, oculist, to whom I am
greatly beholden for the assistance given in these and other tests to be
mentioned presently. In not one of the nine cases did we discover
anything like the curved deflection which is supposed to be the sign of
the form of astigmatism in question. But in order to test objectively
whether Berlin's assumption were justified, we examined in the
laboratory fresh specimens taken from two horses. The eyes were fastened
in a frame in what corresponded to their normal position. Their
posterior spherical wall (i. e., their respective retinal surface) was
replaced by a piece of ground glass. On a spherical surface linear
movements of a point of light are always imaged as curves, no matter
what the shape of the lens forming the image may be. (For a more
detailed statement see page 170, at close of note.) Since, however, our
investigation had to do only with those curves which were due to the
qualities peculiar to the lens, we had to replace the spherical by a
plane projection surface. In front of the eye thus modified a strong
light was placed at such a distance that the image of it, produced on
the improvised back of the eye by the cornea and the lens, was a sharply
defined point of light. Now, when the source of light was moved, the
point of light would also move on the glass plate. Sitting at some
distance behind the eye, we observed the movements of this point through
a telescope. Thus we became witnesses of what happens upon the horse's
retina when a moving object passes in front of his eye. Although we saw
the point of light move through relatively long distances both
horizontally and vertically, no sort of deflection in its pathway could
be noted. Berlin's exposition does not hold true for the eyes of the
horses, either living or dead, which were examined by us.
[Footnote Z: Since no opportunity was given us to examine Hans's
eyes we do not know what their condition is in this respect. Though
it would have been interesting to know, it would hardly make any
difference in the views presented. If Hans should prove to be either
far or near-sighted, then, if we are to make any supposition at all,
it would be that the defect could not be very great, since near
sightedness exceeding 2 or 3 diopters and far-sightedness exceeding
one diopter is seldom found in the case of the horse. According to
Mr. von Osten, Hans at one time manifested a tendency to shy easily.
Be this as it may, for little could be concluded from it, since in
many extremely shy horses, no kind of visual imperfection can be
discovered.]
But in the case of some of the horses in whom Berlin had seen the
phenomenon for which we sought in vain, he himself tells us, the
deflection was very slight. In that case, it would appear, no great
advantage would be gained along the lines indicated. But even assuming
the degree of deflection to be very great, his theory goes to pieces on
the very point it was supposed to explain. A concrete example will make
this clear. If Mr. von Osten, standing two feet away from the horse,
raised his head 1/5 millimeter (which figure by no means represents the
extreme values that were obtained), then in the horse's retinal image
every point of the man's head would move through a distance of 0.0025
millimeter--assuming the horse's eye to be free from astigmatism and
assuming its focal distance to be 25.5 millimeters. If, however, other
conditions remaining the same, we presuppose an extreme form of
astigmatism, one in which the path of the retinal image is not a
straight line, but is deflected into a semicircle, then each point would
pass through a distance of nearly 0.004 millimeter. If the sensitive
retinal elements have a diameter of 0.002 millimeter (as Berlin,
somewhat inexactly, states), then from two to four elements would be
stimulated in case there were no astigmatic deflection. But in case the
deflection did take place, it would not necessarily involve more
elements, as can be seen by making a simple graph; indeed we can imagine
cases in which the circuitous path would involve even fewer elements
than the straight one. And finally, when the movement which the horse is
to perceive, does not occur in a straight line but in the form of a
curve, (which will generally be the rule), then the astigmatism will
tend in many cases to decrease the curvature of the image's path on the
retina, and sometimes even obviate it entirely. In all these cases, on
Berlin's own theory, the perception of the movements would be hindered
rather than aided.[AA]
[Footnote AA: For the benefit of specialists I would say the
following in addition to the more general remarks just made. For the
most part, the determinations of refraction made on the eye of the
horse are still rather unreliable. In sciascopy there is a dispute
among investigators concerning ambiguous shadows, and in the use of
the refraction-ophthalmoscope no definite region of the eye's
background has been adhered to by the various investigators. It
appears that Riegel, whose diligent researches mentioned on page 164
were published in 1904, knew nothing concerning the round area in
the horse's eye, discovered by I. Zuern[42] in 1902. Also, if so
great a degree of astigmatism is really the rule as is emphasized
especially by Hirschberg[43] and Berlin,[44] then the simple
refractive index usually given--sometimes within a half
diopter--would be meaningless. Berlin[45] and Bayer[46] believe the
vagueness of the retinal image resulting from the astigmatism, is
offset by this: that the oval pupil functions as a stenopaic slit.
In view of the width of the horse's pupil this appears to me to be
rather hypothetical.
Concerning Berlin's theory of deflecting astigmatism I would say the
following: Of the two ophthalmoscopic signs mentioned as being
characteristic of this form of astigmatism,--the concentric circles
and the arcuate deflection of the pathway of the fixated
points,--when there is a movement of the eye of the observer (or of
the eye observed), according to Berlin the former is not so constant
as the latter. So far as I know, the concentric ring formation is
mentioned only by Bayer[47] and Riegel,[48] and is said to occur
principally in horses with myopic vision--and hence, relatively, in
a minority of cases. Judging from the particulars, we are inclined
to believe that a case of "Butzenscheiben"-lens reported by
Schwendimann[48_a_] is in reality a case of senile sclerosis.
Berlin repeatedly warns us against mistaking the one for the
other.[48_b_] The arcuate deflection, on the other hand, has not
been mentioned elsewhere as a personal observation. In Berlin's
calculation[49] of the increase in the extent of the retinal pathway
an ambiguity has crept in. He says that "in the astigmatic eye there
are stimulated 207 times as many nervous elements as would be
stimulated in the ideally normal eye." It ought to read "207 more"
instead of "207 times as many." And this number holds only for the
one case computed by Berlin, and under the specific assumption that
exactly [Greek: pi]/2 times the normal number of elements were
stimulated (571 instead of 364). Therefore the general statement
which Bayer[50] makes in his text-book, that according to Berlin's
evaluation "207 times more nervous elements" are stimulated in the
astigmatic eye than in the non-astigmatic one, does not hold true.
Closing this note, a few remarks concerning the experiments made by
Dr. Simon and myself. All of the nine horses were tested for the
vertical image by means of the ophthalmoscope. In most cases Wolff's
electric speculum was used. Atropine was not employed.--For the
laboratory tests the adipose and the muscular tissues were removed
from the eye-ball and the rear part of the bulb cut away. The front
part, containing the cornea and the lens, was fastened over one
opening of a metal cylinder which was closed at the other end by
means of a disc of ground glass. The whole, approximately as long as
a horse's eye, was filled with a normal salt solution whose
refractive index (1.336) corresponds quite closely with that of the
vitreous humor of the horse's eye. The pressure from within was
regulated so that on the one hand it was not dimmed and yet on the
other there were no wrinkles in the cornea. The source of light--the
filament of a Nernst lamp--was moved about in a plane 120 cm.
distant from the eye and perpendicular to the optic axis. It was
moved through the point of intersection as well as at various
distances from it. Movement in horizontal and vertical directions
was in each case along lines 150 centimeters in length, which would
correspond to an angle of vision of not less than 64 deg.. The pathway
of the imaged point was controlled by means of the cross-hairs of
the telescope. If in the same way we observe through the sclerotic
of an intact eye-bulb a point of light falling upon the retina and
shining through the sclerotic and choroid (which is not difficult
when we use an intense light), then to the observer its pathway
will, of course, appear to be deflected convexly toward the
periphery,--and the deflection will appear the greater, the farther
the point of light is removed from the optic axis.]
But to come now to the most pertinent objection. We saw that Berlin's
whole train of thought rested upon the assertion that it made no
difference whether we regarded by means of the speculum the seeming
movement of a fixed retinal point, or whether the image of an external
moving object is passing over the horse's retina. As a matter of fact,
however, these two processes are very different from one another. In
moving the mirror, with its small opening we are looking through ever
changing portions of the horse's lens,--testing it out, as it were. The
horse, on the other hand, sees with all parts of the lens
simultaneously, in so far as the lens is not covered by the iris. The
arcuate deflection, which is nothing but a registration of the
difference in the indices of refraction of the different parts of the
lens used consecutively, might thus be formed for the observer using the
mirror, but never for the horse. For these reasons we cannot conclude
that the kind of astigmatism described can really increase the horse's
acuity in the perception of movements.
Since the light-refracting apparatus of the horse's eye does not offer a
satisfactory explanation for the extraordinary keenness of visual
perception possessed by the Osten horse, we must go a step further and
ask whether it may not perhaps be found in the part immediately
sensitive to light, the retina. That portion really would seem to be
adapted to the perception of movements of minimal extent, and for this
reason: it is more than three times as great in extent as the human
retina, and the horse's retinal images are likewise larger owing to the
position of the nodal point. The cells of the retina that are sensitive
to light, the rods and cones, might therefore be correspondingly larger
than those of the human eye, without thereby making the whole organ less
efficient than the human eye. But the most recent measurements[51] have
shown that the rods and cones of the horse's eye are more minute than
ours. Assuming that, in the case of the horse, as is presumably the case
in human vision, the transition of a stimulus from one retinal cell to
the next already in itself induces a sensation of movement, then the
horse ought indeed be extraordinarily keen in the perception of moving
objects (provided that the horse's more minute cells are packed just as
closely as in the human retina). And besides, there are two specially
adapted areas within the retina of the horse. The "band"
("streifenfoermige Area") which was discovered fifteen years ago by
Chievitz,[52] is a strip of 1 to 1-1/2 millimeters in width, traversing
the entire retina horizontally, and is noteworthy on account of its
structure and probably, too, on account of its greater efficiency. It
may have something to do with the accomplishments of the Osten horse;
but in how far it would be hard to say. The other noteworthy portion of
the horse's retina is the "round area" discovered some four years ago,
located at the rear outer end of the "band", and it is the best-equipped
part of the horse's retina and corresponds to the area of clearest
vision, the yellow spot, in the human eye. But this round area need not
come in for consideration by us, for its location would indicate that it
is used in binocular vision, that is, seeing with both eyes.[53] But in
all our experiments the Osten horse observed only with one eye. That
does not mean, however, that under other circumstances the round area
may not be of very great importance.
In the present state of our knowledge, all attempts at explanation are,
of course, of the nature of hypotheses. If further investigations should
disclose this explanation to be untenable, then we would either have to
suppose some unknown power in the eye of the horse,[AB] or else seek a
cause in the animal's brain. Further experiments on other horses would
be necessary in order to discover whether the species as a whole
possesses this ability or whether only certain ones are thus endowed.
The former is of course more probable. In this particular case
conditions were unusually favorable for the development of this
ability. We must bear in mind that in all probability Mr. von Osten's
movements very gradually became as minute as they are now, and that
therefore Hans at first learned to react to such as were relatively
coarse. Furthermore, his practice extended throughout four years and
during this time it was his sole occupation. Without specific
predisposition, however, all this practice would have been utterly
futile. We can also readily appreciate how indispensable in the struggle
for existence a well-developed power of perceiving moving objects must
be to horses (and most other animals) living in their natural condition
and habitat, in order to be aware of the approach of enemies, or, in the
case of carnivora, the presence of prey. In view of all these
considerations we can readily see how it was possible that the horse,
perhaps in spite of rather defective vision, could react with precision
to movement-stimuli which escaped observation by human eyes.
[Footnote AB: Koenigshoefer, who as we have already said, seconds the
explanation given by the ophthalmologist Berlin (and who confounds
"Butzenscheiben" astigmatism with the common, so-called regular
form), believes[54] that not only astigmatism but also the shape of
the blind-spot of the eye must be taken into consideration. This
portion of the retina, where the fibres of the optic nerve enter the
eye (and called "blind-spot" because there are no cells there that
are sensitive to light) is very nearly circular in man, but differs
in shape in the different species of animals. Koenigshoefer thought he
had discovered that a relatively elongated blind spot was favorable
to keenness of vision. If we place the mammalia in series on the
basis of their relative keenness of vision, he says, we would find
that this series is identical with the one in which they are grouped
with reference to the form of the blind-spot from the circular up to
the most elongated. (In such a series the marmot takes the place of
honor.)
This exposition is not very satisfactory, however. We cannot be sure
what he means by "keenness of vision" ("scharfaeugigkeit"). Is it
visual acuity in the usual sense of the term (as is said in one of
his passages), or keenness in the perception of the movements of
objects, (this would appear to be his real meaning), or both at the
same time. But whatever the significance he may put into the term,
any such attempt at grouping the lower forms must prove
unsatisfactory from the very start on account of the scant data
which we possess on visual perception in animals. The experiences of
the hunt upon which Koenigshoefer partly bases his view, are entirely
inadequate for such a purpose. This much is certain, that the Osten
horse, in spite of a blind-spot which, though somewhat oval, is by
no means very elongated, possesses an extraordinary acuity in the
perception of movements. Even if the parallelism mentioned by
Koenigshoefer were really shown to exist, it would not explain the
matter until it were also shown in what way keenness of vision is
dependent upon the shape of the blind-spot,--a portion of the eye
which is not immediately operative in the visual sensation at all.]
We can understand also the horse's never-flagging attentiveness when we
recall that self-preservation prompts eternal vigilance over against all
that is going on in the animal's environment. (In the case of Hans,
hunger was at first the motive; later, habit did the work.) Furthermore,
the lower form is not hindered in giving itself over to its
sense-impressions by the play of abstract thought which tends so
strongly to direct inward our psychic energy,--at least, in the case of
the cultured.
Nevertheless, Hans still remains a phenomenon not only in excelling all
his critics in the power of observation, but also in that he is the
first of his species, in fact the first animal, in which this
extraordinary perceptual power has been proven experimentally to be
present. It has long been known[55] that horses could be trained to
respond to cues in the form of slight movements, which remained
unnoticed by the layman, and this fact has been made use of by circus
trainers to its fullest extent. But such signs, I have discovered, are
without exception, of a far coarser sort than those we have here
described, and they can be instantly detected by the practised observer.
Nor was it known to professional trainers that it was possible for the
master to direct a horse to any point of the compass simply by means of
the quiet posture of the body. For this reason it was believed that no
signs could possibly be involved in the color-selecting-tests (cf.
Supplement III, page 255). In this we have the support of some of our
experts, as is witnessed by the following extract from a letter of his
Excellency Count G. Lehndorff, one of our best hippological authorities,
who at one time carefully examined the Osten horse. (The letter was
addressed to Mr. Schillings, and I have permission of both gentlemen to
use it). In it he says: "If the author's statements, in which you also
have concurred, are correct, and if, as a matter of fact, the horse
really does react to such minute movements as are absolutely
imperceptible to the human observer, then we have indeed something quite
new, for hitherto no one would have believed that horses can perceive
movements which man cannot. But I am even more surprised by the
explanation of the color-selecting feats.--This too, is something
absolutely new. One would not have deemed it possible that a horse could
do anything of the kind simply by using the posture of a man's body as a
cue to which it could react with such precision."