Why do people so often have trouble telling those of a different race apart? Now psychologists have identified the brain mechanism responsible for this “other-race effect”, and say their work could be used to improve the reliability of eyewitness evidence in criminal trials.

Previous studies have identified the brain region responsible for the phenomenon, but the mechanisms underlying it have been unclear. So Roberto Caldara and colleagues of the University of Glasgow, UK, showed 24 Caucasian and East Asian volunteers pairs of photos, one after the other. The pictures were either of two different people of the same racial group – either Caucasian or East Asian – or the same person with different facial expressions. At the same time they recorded the volunteers’ brain activity using electroencephalography (EEG), which measures electrical activity produced by the firing of neurons in the brain.

Normally, showing someone the same face twice generates a similar EEG pattern each time, although the activity levels is lower the second time. Different faces spark different activity patterns.

When Caldara’s volunteers were shown faces of people of a different race to their own, their neurons responded as if they were the same person, whether they were or not. The results were the same whether Caucasian volunteers were looking at East Asian faces or vice versa.


Universal failure

“That suggests it’s a universal phenomenon in our perception,” says Caldara, who adds that people who live among people of other races can learn to identify individuals better.

Caldara says his team’s techniques could help identify unreliable witnesses in criminal trials. “If a witness has a really clear other-race effect, we could not be sure that they had really recognised a defendant of another race,” he says.

The research is “fascinating”, says John Brigham of Florida State University in Tallahassee, but he thinks that the technique is far from ready to be used in court.

Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1005751107