Autumn 2009: Of Note

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Ben Basile/Special

Humans see, monkeys too

Researchers discover new similarities

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By Carol Clark

Why does this image of a face appear normal when viewed upside down, but clearly shows that it is distorted when right-side up?

It’s a phenomenon known as the Thatcher effect, named for Margaret Thatcher, because it was first demonstrated using an image of the former British prime minister. This human face (in the case above, undergraduate researcher Dina Chou) has been “thatcherized” by positioning the eyes and mouth upside down relative to the rest of the face.

Emory researchers have shown for the first time that another species shares a susceptibility to this illusion: rhesus monkeys (thatcherized images below).

The study, published in Current Biology, “shows that primates are keenly sensitive not just to the features in upright faces but to the relations among those features. This sensitivity is thought to underlie the ability to discriminate among many similar faces—a skill necessary to distinguish kin from non-kin, friend from foe,” says lead researcher Robert Hampton of the Yerkes National Primate Research Center and the Department of Psychology. “This ability probably evolved at least 30 million years ago in an ancestor humans share with rhesus monkeys.”

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