Clever Hans

Clever Hans (German: der Kluge Hans; c. 1894 – c. 1916) was a horse that appeared to perform arithmetic and other intellectual tasks during exhibitions in Germany in the early 20th century. In 1907, psychologist Oskar Pfungst demonstrated that the horse was not actually performing these mental tasks, but was watching the reactions of his trainer. 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, this type of artifact in research methodology has since been referred to as the Clever Hans effect and has continued to be important to 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.