Deep Learning, Meet Clever Hans

Around 1900, a German farmer made an extraordinary claim: he had taught a horse basic arithmetic, and even to read and spell! Indeed, in public demonstrations, the horse, called Clever Hans, was able to answer all of its owner's questions correctly, by a sequence of taps of its hooves. Oskar Pfungst, a psychologist of the time at the University of Berlin, did not quite believe the animal really possessed such human-like capabilities and designed a set of experiments to prove the farmer's claim wrong. In 1907 he published his famous report on the matter, making a surprising observation: Clever Hans would only give the correct answer if the answer was known by the experimenter asking the question! The horse had not actually learned to solve the question by calculating or reading, but rather it recognized subtle cues in the experimenter's body language to figure out what answer was expected of it.