Sunday, August 23, 2009

Clever Hans Effect

Clever Hans (in German, der Kluge Hans) was a horse that was claimed to have been able to perform arithmetic and other intellectual tasks.

After formal investigation in 1907, psychologist Oskar Pfungst demonstrated that the horse was not actually performing these mental tasks, but was watching the reaction of his human observers. Pfungst 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 had the faculties to solve each problem. The trainer 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.

Rico (born December 1994) is a border collie dog who made the news after being studied by animal psychologist Juliane Kaminski from the Max Planck Institute for Evolutionary Anthropology in Leipzig after his owners reported that he understood more than 200 simple words. Kaminski wrote in Science that these claims were justified: Rico retrieved an average of 37 (out of 40) items correctly. Rico could also remember items' names for four weeks after his last exposure.

Rico also responded correctly to a new word with a single exposure, apparently using a canine equivalent of the fast mapping mechanism used by humans. Subject to the anti-Clever Hansing protocols above, a new object was placed alongside seven familiar objects. Rico was told to retrieve the new object, using a word that he had never heard before. Not only could Rico correctly retrieve the object, he also responded correctly to the name of the new object, presumably using a process of elimination.

According to Julia Fischer, "[Rico's ability] tells us he can do simple logic . . . It's like he's saying to himself, 'I know the others have names, so this new word cannot refer to my familiar toys. It must refer to this new thing.' Or it goes the other way around, and he's thinking, 'I've never seen this one before, so this must be it.' He's actually thinking."

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