In Folha, Viana tells the story of the horse that could calculate.
Imagem: Flickr
Reproduction of Marcelo Viana's column in Folha de S. Paulo.
About 120 years ago, one of the greatest celebrities in world science was Kluge Hans (Clever John, in German), the horse that, according to its owner, knew how to add, subtract, multiply, divide, work with fractions, tell the time, and calculate the days of the week.
The owner, mathematics professor and amateur horse trainer Wilhelm von Osten, exhibited Hans publicly, without charging admission, much to the astonishment of the audience. For example, when Von Osten asked, "If the eighth day of the month is a Tuesday, on what date does the following Friday fall?" Hans would respond by tapping his hoof on the ground 11 times.
Skeptics said it was a hoax, that Von Osten was passing the answers to the animal through signals. But Hans was always right even when his owner was absent and the questions were asked by someone else. The legend of the calculating horse continued to grow.
Given the public interest, the German educational authority created a commission of 13 experts to investigate the phenomenon. Besides the psychologist Carl Stumpf, who chaired it, it included a veterinarian, a circus manager, a cavalry officer, several teachers, and the director of the Berlin Zoo. In September 1904, the report was released, exonerating Von Osten of any trickery.
So, biologist and psychologist Oskar Pfungst decided to test the horse's abilities under different conditions: using other people to question Hans; isolating the questioner and the horse from the public; varying whether Hans could see the questioner or not; and even whether the questioner knew the answers or not.
In this way, he confirmed that it didn't matter who asked the questions, proving that there was no bad faith on Von Osten's part. On the other hand, Pfungst found that Hans only answered correctly when he could see the questioner and the questioner knew the answers! In some subconscious way, the questioner passed the answers to the horse… And this happened even when Pfungst himself was the one asking the questions!
The discovery brought discredit upon poor Hans, which was very unfair: even though he wasn't capable of calculating, Hans was a remarkable animal, with an extraordinary ability to read human facial expressions and body language, better than we ourselves are capable of.
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