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Clever Hans

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Horse who performed math tricks (1890s–1910s)

For Grimm's tale, see Clever Hans (fairy tale).

Clever Hans performing in 1904<br>Clever Hans (German: der Kluge Hans; c. 1894 – c. 1916) was a horse that appeared to perform arithmetic and other intellectual tasks during exhibitions in Germany in the early 20th century.

In 1907, psychologist Oskar Pfungst demonstrated that the horse was not actually performing these mental tasks, but was watching the reactions of his trainer. The horse was responding directly to involuntary cues in the body language of the human trainer, who was entirely unaware that he was providing such cues.[1] In honour of Pfungst's study, this type of artifact in research methodology has since been referred to as the Clever Hans effect and has continued to be important to the observer-expectancy effect and later studies in animal cognition.<br>Pfungst was an assistant to German philosopher and psychologist Carl Stumpf, who incorporated the experience with Hans into his further work on animal psychology and his ideas on phenomenology.[2]

Spectacle<br>[edit]

Wilhelm von Osten and Clever Hans<br>During the early twentieth century, the public was especially interested in animal cognition owing in large part to Charles Darwin's recent publications. The case of Clever Hans was taken to show an advanced level of number sense in an animal.

Hans was a horse owned by Wilhelm von Osten, who was a gymnasium mathematics teacher, an amateur horse trainer and phrenologist and was considered to be a mystic. Hans was said to have been taught to add, subtract, multiply, divide, work with fractions, tell the time, keep track of the calendar, differentiate between musical tones, 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 hoof eleven times. Questions could be asked both orally and in written form. Von Osten exhibited Hans throughout Germany and never charged admission. Hans' abilities were reported in The New York Times in 1904.[3]

After von Osten died in 1909, Hans was acquired by several owners. He was then drafted into World War I as a military horse and "killed in action in 1916 or was consumed by hungry soldiers".[4]

Investigation<br>[edit]

The great public interest in Clever Hans led the German board of education to appoint a commission to investigate von Osten's scientific claims. Philosopher and psychologist Carl Stumpf formed a panel of 13 people, known as the Hans Commission. This commission consisted of a veterinarian, a circus manager, a cavalry officer, a number of schoolteachers, and the director of the Berlin zoological gardens. This commission concluded in September 1904 that no tricks were involved in Hans's performance.

The commission passed off the evaluation to Oskar 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 gave the right answer only when the questioner knew what the answer was and the horse could see the questioner. He observed that when Hans could see the questioner, the horse got 89 percent (50 out of 56) of the answers correct, but when Hans was not able to see the questioner, the horse answered only six percent (2 out of 35) of the questions correctly.[5]

Pfungst was aware of the ability of circus trainers to train horses to respond to small gestures, and was aware of a number of cases of dogs, like that of English astrophysicist Sir William Huggins, who were able to point to an object their master was looking at or who were able to "bark" the answer to questions like square roots while staring at their master's face, and so after refuting his initial suspicion of a fraud involving whispering or the like, began to consider accidental communication with Hans.[6] Pfungst then examined 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...