The Clever Hans effect

In the early twentieth century, one called Clever Hans appeared to be able to do some basic arithmetic, repeatedly and reliably tapping his hoof the same number of times as the right answer to a sum set for him to solve. When investigated, it was discovered that Hans was actually responding to changes in the posture and expression of onlookers, who visibly relaxed when he got to the right number. What psychologists call the Clever Hans Effect might well be what enables a child to correctly identify the lama’s possessions.

Saved 23 April 2015

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