Clever Hans

Scientists may have been growing cautious in their speculations about the mental abilities of animals, around 1900, but the public showed an undiminished appetite for stories of animal consciousness. Newspapers and magazines published serious articles about dogs, cats, and horses with human-like intelligence. Ten years after Morgan's Canon, many people believed newspaper stories about a German horse that could read and write.

The year was 1904 when retired Berlin schoolteacher Wilhelm von Osten presented Clever Hans to the world. The horse could apparently understand German, do arithmetic, interpret calendars, and perform other amazing intellectual feats.


Von Osten and his pupil, Clever Hans

Von Osten created a letter board on which each letter of the alphabet was assigned a number. The horse spelled out answers to questions by tapping its hoof the number of times corresponding to each letter, forming words and sentences.

How did von Osten train Hans?

At first von Osten held the horse's hoof, named a letter, and tapped the appropriate number of times. After many repetitions, the horse appeared to "catch on" and von Osten withdrew his hand gradually. (This resembles the technique described in Chapter 5 as prompting and fading.)

Now the horse tapped the appropriate number of times whenever a letter was named. Soon Hans was taught to spell out words, then whole sentences, using the appropriate number of hoof-taps for each letter of the alphabet. Von Osten went on to teach Hans arithmetic and other skills.

It took about two years to complete the training which made the horse so famous. It mastered the four fundamental rules of arithmetic, changed common fractions into decimals and back again, and could give the day of the month. It knew how to tell the time by the clock and could, for example, answer the question, "Between which figures is the small hand when it is twenty-five to eight?" The horse also had an astonishing appreciation of music. If one played the dominant seventh chord D, F, A, C, it shook its head and indicated that the C should be left out to turn it into a more harmonious minor chord. (Katz, 1953)

What remarkable abilities did Clever Hans appear to possess?

Who believed in Clever Hans? The psychiatrist Gustav Wolff did, among others. He issued a statement declaring "that an animal can think in a human way and can express human ideas in human language." He was joined in this opinion by "prominent scholars, scientists, psychologists, psychiatrists, medical doctors, and many others" (Hediger, 1981).

Why was it obvious no "cheating" was involved?

One reason so many prominent authorities believed in Clever Hans was that the horse could perform in the absence of its trainer. This made it appear that no cheating was possible. A commission of zoologists evaluated the animal, and they concluded that no trickery was involved.

Oskar Pfungst from the Berlin Psychological Institute finally solved the puzzle. He showed that Hans could answer a question only when somebody near the horse knew the answer. If the question was presented to the horse by somebody who then left the scene, leaving only people who did not know the answer to the question, Hans never stopped tapping. Under those circumstances, Hans tapped slowly, hesitated and appeared to watch the observers very closely...and continued to tap.

What did Pfungst conclude about Clever Hans's abilities?

Pfungst deduced that Hans was reacting to tiny cues given off by observers. Evidently when Hans approached the correct number of hoof taps (completing a word, for example) the human observers reacted in some way that the horse could detect. Perhaps they raised and lowered their eyebrows, or took a deep breath. When Hans perceived these subtle cues, he would stop tapping to get his reward. Pfungst was able to get the horse to give any answers he chose by making similar tiny movements.

How were "no-go" signals involved? Were the signals given consciously?

Using the terminology of animal trainers, Clever Hans was responding to a "no-go" or "stop what you are doing" signal. His reward for paying attention to these signals was the social reinforcement of an approving crowd. The crowd (and even von Osten) was not conscious of giving this type of signal. Pfungst concluded:

In the course of the long series of lessons in arithmetic, the horse must have learned to spot more and more accurately the tiny body movements with which the teacher unconsciously accompanied his own thinking. These movements the horse learned to utilize as cues....The horse's performance and the great accuracy it achieved in perceiving these tiniest of movements remain amazing. (In Katz, 1953, p.15)


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