Clever Hans

Pfungst was an assistant to German philosopher and psychologist Carl Stumpf, who incorporated the experience with Hans into his further work on animal psychology and his ideas on phenomenology.

[1] Hans was said to have been taught to add, subtract, multiply, divide, work with fractions, tell the time, keep track of the calendar, differentiate between musical tones, and read, spell, and understand German.

[4] The great public interest in Clever Hans led the German board of education to appoint a commission to investigate von Osten's scientific claims.

[5] Pfungst was aware of the ability of circus trainers to train horses to respond to small gestures, and was aware of a number of cases of dogs, like that of English astrophysicist Sir William Huggins, who were able to point to an object their master was looking at or who were able to "bark" the answer to questions like square roots while staring at their master's face, and so after refuting his initial suspicion of a fraud involving whispering or the like, began to consider accidental communication with Hans.

He frequently observed "a sudden slight upward jerk of the head" when reaching the final tap, and noted that this corresponded to the subject resuming the position they had adopted before thinking of the question.

[citation needed] Recognition of this phenomenon has had a large effect on experimental design and methodology for all experiments whatsoever involving sentient subjects, including humans.

If the results of such studies are to gain universal acceptance, it is necessary to find some way of testing the animals' achievements which eliminates the risk of Clever Hans effects.

This study proved that, for this pointing task, there was no Clever Hans effect affecting the dogs' performance, as long as the owners did not actively influence them.

[8] Similarly, a study done in 2013 also examined whether a Clever Hans effect was present in a two-way object choice test and included an experimental group in which the owners actively tried to influence their dog's decision.

Another way in which Clever Hans effects are avoided is by replacing the experimenter with a computer, which can deliver standardized instructions and record responses without giving clues.

In the field of Artificial Intelligence, the Clever Hans effect describes a phenomenon where an algorithm seems to make correct predictions without having the relevant data and/or by using incorrect reasoning.

[13] Based on the information from Oskar Pfungst's book "Clever Hans" (1911),[6] the installation shows an animated horse and uses facial detection and pose estimation to predict which number a person is currently thinking about.