Clever Hans
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Clever Hans (in German, der Kluge Hans) was a horse that was claimed to have been able to perform arithmetic and other intellectual tasks.
After formal investigation in 1907, psychologist Oskar Pfungst demonstrated that the horse was not actually performing these mental tasks, but was watching the reaction of his human observers. Pfungst discovered this artifact in the research methodology, wherein the horse was responding directly to involuntary cues in the body language of the human trainer, who had the faculties to solve each problem. The trainer was entirely unaware that he was providing such cues.
In honour of Pfungst's study, the anomalous artifact has since been referred to as the Clever Hans effect and has continued to be important knowledge in the observer-expectancy effect and later studies in animal cognition.
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[edit] Spectacle
During the late nineteenth century, the public was especially interested in animal intelligence due in a large part to Charles Darwin’s then recent publications.
Hans was a horse owned by a Mr. von Osten, who was a highschool math teacher, an amateur horse trainer and phrenologist, and something of a mystic. Hans was taught to add, subtract, multiply, divide, work with fractions, tell time, keep track of the calendar, differentiate musical tones, and read, spell, and understand German. Von Osten would ask Hans, "if the eighth day of the month comes on a Tuesday, what is the date of the following Friday?” Hans would answer by tapping his foot. Questions could be asked both orally, and in written form. Von Osten exhibited Hans throughout Germany, and never charged admission. Hans’s abilities appeared on page four of the New York Times.
[edit] Investigation
Due to the large amount of public interest, the German board of education appointed a commission to investigate von Osten's scientific claims. Philosopher and psychologist Carl Stumpf formed a panel of 13 prominent scientists, known as the Hans Commission. This commission consisted of a veterinarian, a circus manager, a Cavalry officer, a number of school teachers, and the director of the Berlin zoological gardens. This commission concluded in September, 1904 that no tricks were involved in Hans’ performance. The commission passed off the evaluation to Pfungst, who tested the basis for these claimed abilities by:
- Isolating horse and questioner from spectators, so no cues could come from them
- Using questioners other than the horse's master
- By means of blinders, varying whether the horse could see the questioner
- Varying whether the questioner knew the answer to the question in advance.
Using a substantial number of trials, Pfungst found that the horse could get the correct answer even if von Osten himself did not ask the questions, ruling out the possibility of fraud. However, the horse got the right answer only when the questioner knew what the answer was, and the horse could see the questioner. He observed that when von Osten knew the answers to the questions, Hans got 89 percent of the answers correct, but when von Osten did not know the answers to the questions, Hans only answered six percent of the questions correctly.
Pfungst then proceeded to examine the behaviour of the questioner in detail, and showed that as the horse's taps approached the right answer, the questioner's posture and facial expression changed in ways that were consistent with an increase in tension, which was released when the horse made the final, "correct" tap. This provided a cue that the horse could use to tell it to stop tapping.
The social communication systems of horses probably depend on the detection of small postural changes, and this may be why Hans so easily picked up on the cues given by von Osten (who seems to have been entirely unaware that he was providing such cues). However, the capacity to detect such cues is not confined to horses. Pfungst proceeded to test the hypothesis that such cues would be discernible, by carrying out laboratory tests in which he played the part of the horse, and human participants sent him questions to which he gave numerical answers by tapping. He found that 90% of participants gave sufficient cues for him to get a correct answer.
Even after this official debunking, von Osten, who was never persuaded by Pfungst's findings, continued to show Hans around Germany, attracting large and enthusiastic crowds.
[edit] The 'Clever Hans' effect
Pfungst made an extremely significant observation. After he had become adept at giving Hans performances himself, and fully aware of the subtle cues which made them possible, he discovered that he would produce them involuntarily regardless of whether he wished to exhibit or suppress them. This gives the phenomenon an importance which could hardly be exaggerated. Its recognition has had a large effect on experimental design and methodology for all experiments whatsoever involving sentient subjects (including humans). The risk of Clever Hans effects is one strong reason why comparative psychologists normally test animals in isolated apparatus, without interaction with them. However this creates problems of its own, because many of the most interesting phenomena in animal cognition are only likely to be demonstrated in a social context, and in order to train and demonstrate them, it is necessary to build up a social relationship between trainer and animal. This point of view has been strongly argued by Irene Pepperberg in relation to her studies of parrots, and by Alan and Beatrice Gardner in their study of the chimpanzee Washoe. If the results of such studies are to gain universal acceptance, it is necessary to find some way of testing the animals' achievements which eliminates the risk of Clever Hans effects. However, simply removing the trainer from the scene may not be an appropriate strategy, because where the social relationship between trainer and subject is strong, the removal of the trainer may produce emotional responses preventing the subject from performing. It is therefore necessary to devise procedures where none of those present knows what the animal's likely response may be.
For an example of an experimental protocol designed to overcome the Clever Hans effect, see Rico (Border Collie).
As Pfungst's final experiment makes clear, Clever Hans effects are quite as likely to occur in experiments with humans as in experiments with other animals. For this reason, care is often taken in fields such as perception, cognitive psychology, and social psychology to make experiments double-blind, meaning that neither the experimenter nor the subject knows what condition the subject is in, and thus what his or her responses are predicted to be. Another way in which Clever Hans effects are avoided is by replacing the experimenter with a computer, which can deliver standardized instructions and record responses without giving clues.
[edit] In popular culture
In an episode of The Simpsons ("Smart and Smarter"), Lisa Simpson becomes jealous of her baby sister Maggie after Maggie is "discovered" to have an even higher IQ than the precocious Lisa. Later in the episode, Lisa is relieved to find that she had been unconsciously cueing Maggie's "correct" IQ-test answers.
Australian pop band The Lucksmiths perform a song called "Clever Hans" on their first album. The song features horse imagery but no direct references to its eponymous predecessor.
An episode of The Wild Thornberrys (The Great Bangaboo, airdate: 3/23/1999) features a traveling showman calling himself "The Great Bangaboo" who claims he can talk to animals. To prove this, he performs a show with a donkey that he claims can solve math problems. He displays a card that says "2+2=?" to the audience, then "asks" the donkey for an answer by letting out a plain and simple "Hee-haw!" The audience sees the donkey stomping his foot four times as if to say the answer to "2+2?" is four. However, an intentional view from backstage reveals that the showman pulls with his cane on a tangled system of ropes attached to a broom that pokes the donkey through a covered-up hole in the backdrop, making the donkey instinctively stomp his foot.
[edit] Trivia
- Both von Osten and Hans were notoriously bad tempered and prone to rage when the horse did not perform well. Pfungst suffered more than one horse bite during his investigation.
[edit] Sources
- Pfungst, O. (1911). Clever Hans (The horse of Mr. von Osten): A contribution to experimental animal and human psychology (Trans. C. L. Rahn). New York: Henry Holt. (Originally published in German, 1907).
[edit] See also
- Pygmalion effect
- Lady Wonder a horse with purported telepathic abilities.
[edit] External links
