166. ‘Clever Hans’ the Mathematical Horse

05 Jul

In the early twentieth century there was a spectacle, a horse called ‘Clever Hans,’ whom the owner claimed could add, subtract, multiply, divide, work with fractions, tell time, keep track of the calendar, differentiate musical tones, and read, spell, and understand German. Truly a spectacle, bolstered by the sudden interest in animal intelligence thanks to the then fairly recent publication of Darwin’s, ‘On The Origin Of Species.’

Propelled by this interest ‘Clever Hans’ quickly gained repute and fame for both himself and his trainer, Wilhelm Van Osten, a mathematics teacher and an amateur, but in this case successful, horse trainer. Van Osten held spectacles for which he never charged entry, he would gather a crowd, ask Hans a question and Hans would tap the answer out until the right number was reached. For example he would ask,’If the eighth day of the month comes on a Tuesday, what is the date of the following Friday?’ The Hans would tap his hoof the requisite number of times(in this case 11).

Question could be submitted either verbally or in written form. The success of the spectacle allowed ‘Hans’ and van Osten to travel widely across Germany and in fact the whole event was featured at one point on page six of the New York Times. Then came queries, exactly how did the horse do it? Due tot he popularity and wide speculation the German board of education put together a committee of 13 people in order to test the scientific claims being made. They were known as the Hans committee.

The committee consisted of a philosopher/psychologist, a veterinarian, a circus manager, a cavalry officer, the head of the Berlin zoological gardens and a various school teachers. They then performed rigorous tests and they found that ‘Clever Hans’ would get the answers correct, regardless of who asked the question. So fraud was ruled out. Then they noticed something odd, if the questioner knew the answer, Hans would get it correct 89% of the time, if the questioner didn’t know the answer, Hans would only get it right 6% of the time.

The hypothesis that ‘Clever Hans’ could read minds seems apt at this point, but was never seriously considered. There was something far more simple at work than a telepathic horse. The answer was the horse couldn’t read minds, but it could read bodies.

As ‘Clever Hans’ would tap his hoof, the closer he got to the answer the more the questioner would tense up, showing slight changes in posture and facial expression. When the final correct tap was placed, any questioner would relax, and so Hans would stop. 90% of people produced noticeable changes. In fact, even when told, people just couldn’t stop providing these clues, and so Hans responded. This was evidence of an animal reacting to people, not the stimulus that people thought it was reacting to. This small phenomenon was name the ‘Clever Hans effect.’

The investigation concluded in September 1904, stating that ‘Clever Hans’ was not able to perform all of the claimed calculations and interpretation of German, the horse was debunked. However his trainer was unconvinced with the conclusion and continued to parade ‘Clever Hans’ around Germany, attracting large and enthusiastic crowds.

5 years after the investigation van Osten died, and so in 1909 ‘Clever Hans’ was acquired by several owners. He was rumored to have some involvement in World War I. After 1916 all records of him stop. His fat to this day remains unknown.

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Posted by on July 5, 2011 in Articles, Misconceptions, Trivia


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