Clever Hans | EPFL Graph Search

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Clever Hans (German: der Kluge Hans; c. 1895 – c. 1916) was a horse that was claimed to have performed arithmetic and other intellectual tasks. After a formal investigation in 1907, psychologist Oskar Pfungst demonstrated that the horse was not actually performing these mental tasks, but was watching the reactions of his trainer. He discovered this artifact in the research methodology, wherein the horse was responding directly to involuntary cues in the body language of the human trainer, who was entirely unaware that he was providing such cues. In honour of Pfungst's study, the anomalous artifact has since been referred to as the Clever Hans effect and has continued to be important knowledge in the observer-expectancy effect and later studies in animal cognition. 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. During the early twentieth century, the public was especially interested in animal intelligence owing in large part to Charles Darwin's recent publications. The case of Clever Hans was taken to show an advanced level of number sense in an animal. Hans was a horse owned by Wilhelm von Osten, who was a gymnasium mathematics teacher, an amateur horse trainer, phrenologist, and considered a mystic. Hans was said to have been taught to add, subtract, multiply, divide, work with fractions, tell time, keep track of the calendar, differentiate between musical tones, and read, spell, and understand German. Von Osten would ask Hans, "If the eighth day of the month comes on a Tuesday, what is the date of the following Friday?" Hans would answer by tapping his hoof eleven times. Questions could be asked both orally and in written form. Von Osten exhibited Hans throughout Germany, and never charged admission. Hans's abilities were reported in The New York Times in 1904. After von Osten died in 1909, Hans was acquired by several owners. After 1916, there is no record of him and his fate is unknown.

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