This is Hidden Brain, I'm Shankar Vedanta.

All of us know what prejudice looks like.

We've seen news stories about swastikas pre-painted on synagogues

or news is drawn on classroom walls to terrorize black students.

We have heard xenophobic speeches from politicians

and watched in horror as ethnic groups around the world

have exterminated their enemies.

In the late 1990s, Harvard psychologist Maserine Bananjee

and her former PhD advisor, Tony Greenwald of the University of Washington,

developed a test of hidden bias called the implicit association test or IAT.

Unlike the very public spectacle of a burning cross on someone's front lawn,

the picture of bias painted by this test was rather subtle.

By measuring the speed of people's associations,

the tests showed that large numbers of Americans found it easier to associate white faces with

positive concepts than to associate black faces with positive concepts.

Many people were similarly quick to associate men with professional activities

and slow to associate women with such activities.

Lots and lots of Americans appear to have negative associations about the elderly.

The overweight and the disabled.

Crucially, large numbers of the people taking the tests didn't think of themselves as being

prejudiced. Many prided themselves on having egalitarian beliefs.

Their test results often came as a shock.

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