Clever Hans and his Effect on Psychology

In 1904 Stumpf was asked to head a special commission to investigate whether a horse, Clever Hans, could actually perform all of the advanced mental tasks his trainer and

---------------Insert Figure 8.3 about here [von Osten and Clever Hans]---------------

owner, Wilhelm von Osten, claimed he could. Hans had been observed to add, subtract, multiply, divide, take square roots, tell time, and much more. The horse indicated his answers by tapping his foot. For example, when shown a card with the numbers:

2 + 3 =

Hans would tap five times. He usually got the correct answer. His owner claimed that it was the way he had taught Hans that had made the difference. The special commission consisted of 13 members and included a cavalry officer, a circus owner, the director of the Berlin Zoo, a veterinarian, a magician, and others. The commission, after studying the owner and his horse concluded that no trickery was involved and that von Osten’s instructional methods must account for the horse’s remarkable performance. Just to be sure, however, they left one of Stumpf’s students, Oskar Pfungst, behind to conduct a more thorough investigation.

Pfungst (1911) described his patient and thorough investigations on Hans and on his owner. He discovered that Hans could answer correctly even when others were asking the questions. When he had von Osten ask questions to which he himself did not know the answer, Han’s performance dropped to the level of chance. When he looked more closely at von Osten as he asked the questions (ones that von Osten knew the answer to) he noticed that von Osten was giving Hans nearly imperceptible cues for when to start and stop tapping his hoof. By the time he was finished studying Hans, Pfungst, just through subtle facial and bodily movements, could make the horse start and stop tapping. Apparently, von Osten did not realize he was making such movements. So, Hans was intelligent, in a way. He was intelligent enough to learn to pair the signs that his trainer was giving him with hoof tapping. Pfungst showed the world that Hans was not as smart as a human being and in the process helped demonstrate the utility of the new science of psychology.

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