In a nutshell: Clever Hans was a horse that some people thought could do math in his head and understand German. One group of people tested him and found these claims were true. Another scientist tested Hans and found the claims weren’t true.
Clever Hans (German: Kluge Hans) was a German horse who seemed to be able to do math problems in his head, tell time, name people, and answer questions by tapping his hoof. When asked to add 3 + 2, Hans would tap his hoof five times. If asked my name, Hans would have tapped twice for ‘B’, paused, tapped 15 times for ‘O’, paused, and then tapped twice again.
Hans could even answer hard written questions. Was he really able to read?
“If the eighth day of the month comes on a Tuesday, what is the date of the following Friday?” Hans could figure that out. He answered by tapping his hoof eleven times. This was one smart horse!
Hans’s owner, Wilhelm von Osten, began showing his clever horse to the public in 1891. He did so for about twenty years. Many people, including some scientists, were sure that Hans was really doing some heavy duty thinking. They were certain that his hoof tapping was not a trick. Clever Hans became famous.
The German board of education sent a group of people (the Hans Commission) to study Hans. Carl Stumpf, a philosopher and psychologist, led the commission. A few school teachers, a veterinarian, a director of the Berlin zoo, and a few others joined Stumpf.
The Hans Commission listed some possible explanations for what Hans could do. Maybe he could really understand both spoken and written language. Maybe he could do math in his head. Maybe he was acting on cues his owner was giving.
[ . . . ]
a skeptical scientist tests Hans again
[ . . . ]
Oskar Pfungst (1847-1933), a biologist and psychologist, tested Hans again. He found that the Hans Commission had not done a very good job. Pfungst proved that Hans was responding to very slight movements of those watching him. Hans was especially sensitive to small head movements by his owner. Pfungst also found that the movements by those watching Hans were not done on purpose to cue the horse. If asked to add 3 + 2, for example, the horse would start tapping. When he got to five taps, von Osten (or others watching Hans) would lean forward very slightly and that was the cue for the horse to stop tapping.
How did Pfungst figure this out?
He set up a test where the horse could be asked questions but could not see von Osten or others who were watching. He put blinders on Hans. When the horse couldn’t see anyone, he didn’t respond. In another test, the horse didn’t respond when the one asking the question didn’t know the answer to it. But the horse did give the right response when the one asking the question did know the answer to it, even if von Osten was not present. That last test ruled out the hypothesis that von Osten knew he was signaling Hans. He wasn’t cheating. He really believed his horse was doing math and reading letters. The evidence collected by Pfungst led the scientific community to hold that Hans was responding to slight movements rather than understanding written and spoken words. Von Osten, however, kept on believing that his horse could read, do math, and understand German. He was making a little bit of money showing off Hans and he kept on with his pony show.
One of the beautiful things about science is how one discovery leads to another. One of the things Pfungst found is the ideomotor effect: making slight movements without being aware of making them. (See the entries on dowsing and the Ouija board for other cases of the ideomotor effect.)
While testing Hans, Pfungst discovered that animals respond to movements around them that can barely be seen. He also found that people aren’t always aware that they are moving and giving cues to animals (or other persons). We now know that humans also respond to movements or sounds without being aware of it. We call this giving of signals without awareness unconscious signaling. This discovery has had a major effect on how experiments should be done when they involve either people or animals.
We now know that humans are unconsciously aware of many things right before their eyes. A botanist might see a rare flower out of the corner of his eye and not be conscious of having seen it. Later, he finds himself thinking of that rare flower. Then, he sees the flower and says “wow, I was just thinking of that flower.” Isn’t that amazing? Yes. Scientists call it “sensing without seeing.”