Friday, August 26, 2011

Why do people of other races all look alike?

People often say they find it difficult to distinguish between individuals of other races. Two recent neurophysiological studies point to the underlying brain mechanisms

I've seen The Departed twice, but I still don't understand it. The first time I watched it, I was utterly confused, and the plot still didn't make much sense on the second viewing. I know exactly why this is – it's because I find it very hard to tell the difference between Leonardo DiCaprio and Matt Damon. I've been told that this might have something to do with the "other-race effect," which makes it difficult for us to identify people of other races or ethnic groups. But I'm not so sure – I can easily distinguish Robert DeNiro from Jack Nicholson, or Humphrey Bogart from Cary Grant.

Nevertheless, the other race effect is a well established phenomenon that we've known about for nearly a hundred years. "To the uninitiated American," wrote Gustave Feingold in 1914, "all Asiatics look alike, while to the Asiatics, all White men look alike."

But why does this happen? It could be because we have more experience of members of our own race and so find it easier remembering their faces. Or it could be because people of other races are generally perceived to have fewer unique personal attributes and, therefore, to have more in common with one another. These explanations aren't mutually exclusive, and two recent studies provide evidence for both.

In the first of these studies, Heather Lucas and her colleagues of the Cognitive Neuroscience Laboratory at Northwestern University recruited 18 white female undergraduates and showed them colour photographs of the faces of white, black, Hispanic and east and south Asian adult men, presented in random order on a computer screen. The participants were asked to pay close attention to the faces and try to remember them for a recognition test. Afterwards, they were shown some of the same faces again, as well as some new ones, and asked to indicate whether or not they had seen each one before.

Participants wore an elastic electroencephalography (EEG) cap containing 59 electrodes, so that the electrical activity of their brains could be recorded throughout the experiment. The researchers focused on two event-related potentials, or neural responses associated with particular events – the N200 potential, which is recorded from the frontal lobes and associated with encoding of novel visual stimuli, and the P2 potential in the junction of the occipital and parietal lobes, which is thought to be sensitive to the characteristic features of a stimulus and, in this case, may be associated with extraction of facial features.

As expected, the participants recognised same-race faces more accurately than other-race faces, and this corresponded with larger N200 and P2 responses during the first phase of the experiment. Similarly, other-race faces that were accurately recognised evoked larger N200 and P2 responses than those which were later forgotten. Moreover, the researchers could predict which faces would be accurately recognised during the recall phase from the brain responses alone.

Why were some of the other-race faces recognised more accurately than others? The researchers hypothesised that some might be more distinctive than others, leading to better encoding of unique facial features, and ran a second experiment to test the idea. This time, they showed the same photos to 96 different white females, and asked them to rate how distinctive, stereotypical and approachable each one was, on a scale of one to five. Afterwards, the participants performed the same face recognition test as in experiment one.

In general, other-race faces were rated as being more stereotypical than same-race faces, but those perceived to be more distinctive were rated as less stereotypical. Faces expressing a positive emotion were rated as more stereotypical and approachable, regardless of race. Not surprisingly, the researchers found a relationship between distinctiveness ratings and accuracy of recognition – the more distinctive a face, the more likely it was to be accurately recognised later on.

Analysis of the electrophysiological data revealed that the other-race faces rated as being less stereotypical or more distinctive evoked larger N200 and P2 responses, compared to other-race faces that were rated as less distinctive or undistinctive. By contrast, stereotypicality ratings of same-race faces were not reflected in the neural responses.

Lucas and her colleagues believe this is the first study to correlate electrophysiological recordings with memory performance for other-race faces. They interpret the results to mean that same-race faces are encoded elaborately, with an emphasis on the unique facial features that help us to distinguish one person from another. For other-race faces, however, this individuating information is encoded less robustly. Consequently, we have a poorer memory for other-race faces, and are therefore less likely to recognise them or to distinguish between them. Distinctive other-race faces appear to be an exception, however, and may be processed in a similar way to same-race faces.

The other study comes from Robert Caldara's lab at the University of Glasgow, and looks at how the brain's responses change with repeated exposure to same-race and other-race faces. The brain is well known to adapt to familiar stimuli, so that the neural activity evoked by them decreases with repeated exposure to them. Faces evoke a larger N170 response in the occipital and temporal lobes than other visual stimuli, but the size of this response decreases when the same face is seen again.

Caldara's group recruited 12 white and 12 east Asian participants, and used EEG to monitor the N170 response while they viewed sequences of two faces. In each sequence, the faces were either white or east Asian; some sequences consisted of the same face with a different expression, while others contained faces of two different people. The participants were simply asked to indicate whether or not the two faces in each sequence were the same.

Both groups of participants found it more difficult to identify the other-race faces. This was reflected in the neural activity, too – the N170 response was significantly decreased when participants viewed same-race faces a second time, but not when they saw other-race faces again. Interestingly, the neural responses obtained when the white participants saw the same east Asian face twice were no different from those obtained when they saw two different white faces.

The other-race effect has been consistently observed in whites, but these findings suggest that it may be a generalised response that occurs in people of all races. Caldara and his colleagues put forward an explanation for the "all look alike" phenomenon, based on their findings. The N170 is an early response to visual stimuli, which occurs in a time window associated with categorising objects. The researchers therefore suggest that the other-race effect may occur because the brain encodes other-race faces primarily according to the racial group they belong to, rather than by distinguishing features.

Another factor that is likely to contribute to the other-race effect is familiarity – or, rather, lack thereof. In a 2003 study, researchers showed black and white participants from South Africa and England photographs of black and white faces and then asked them if they had seen each of the faces before. Both groups identified same-race faces more accurately than other-race faces, but some of the black participants could accurately identify white faces.

This was directly related to the amount of inter-race contact – the black participants who were best at recognising other-race faces were students who came into regular contact with whites at university. Feingold had hit the nail on the head in his 1914 paper: "Individuals of a given race are distinguishable from each other in proportion to our familiarity, to our contact with the race as whole."

How, then, can my failure to tell the difference between Matt Damon and Leonardo DiCaprio be explained? It's clearly not because I think all white people look alike – I've been surrounded by them for most of my life, having lived in London for over 30 years. A more likely explanation is that I haven't seen enough of their films to recognise the facial features that others use to tell them apart. Or perhaps they're just not very distinctive, and look very similar to one another.

Costandi, Mo. 2011. "Why do people of other races all look alike?". Guardian. Posted: August 15, 2011. Available online:

Article References:

Lucas, HD et al. (2011). Why some faces won't be remembered: brain potentials illuminate successful versus unsuccessful encoding for same-race and other-race faces. Frontiers of Human Neuroscience. DOI: 10.3389/fnhum.2011.00020

Vizioli, L et al. (2010). Neural repetition suppression to identity is abolished by other-race faces. Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.1005751107

Wright, DB et al. (2003). Inter-racial Contact and the Own-race Bias for Face Recognition in South Africa and England. Applied Cognitive Psychology. DOI: 10.1002/acp.898

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