SUBCONSCIOUS negative feelings or stereotypes about black people are learned through American culture, suggests the first brain imaging study to test both black and white people鈥檚 racial biases.
鈥淚 think the results are very specific to this society, where portrayals of African Americans are not very positive on average,鈥� says Matthew Lieberman at the University of California, Los Angeles, who led the research.
Hidden prejudices have been revealed before with brain scans. Using functional magnetic resonance imaging (fMRI), researchers have found that white Americans show more brain activity in a region called the amygdala when viewing images of black faces than when viewing white faces. The amygdala is involved in emotional reactions and becomes very active in fearful or threatening situations. But it also reacts to novelty, so activity there could just be the result of seeing a less familiar kind of face.
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鈥淏lack faces should not be novel to black people, so they must have learned to associate other black people with a threat鈥�
To test this explanation, Lieberman and his colleagues conducted an fMRI experiment with 11 white and 8 black Americans. Each participant completed three tasks: matching the race of a target photo to one of two comparison photos; matching a target photo to either the words 鈥淎frican American鈥� or 鈥淐aucasian American鈥�; and a control test where they matched geometrical shapes.
鈥淏oth black and white volunteers showed increased amygdala activity on the visual task when the target face was black鈥�
Both black and white volunteers showed increased amygdala activity on the visual task when the target face was black. The same task with a white target face produced no such activity. Because black faces should not be 鈥渘ovel鈥� to black people, Lieberman concluded they must have learned to associate other black people with a threat (Nature Neuroscience, DOI: 10.1038/nn1465).
But assuming that black faces will be less novel to African Americans may be simplistic. Each person鈥檚 history and acquaintances could influence their amygdala response, says Paul Whalen at the University of Wisconsin in Madison.
What鈥檚 more, although the amygdala responds predominantly to negative stimuli, that is not always so. Whalen says that knowing the subject鈥檚 background, rather than their skin colour, will probably reveal more about the meaning of the amygdala鈥檚 response.
However, the brain results are backed up by earlier behavioural test results. These 鈥渋mplicit association tests鈥� (IATs) use subtle tasks, such as the time it takes for subjects to associate ideas of race with either positive or negative words, to uncover unconscious attitudes. Black Americans often show more positive associations for whites in IATs.
Interestingly, it does seem possible to override the amygdala response. When subjects performed the verbal matching tasks there was no difference for black or white faces. 鈥淚n general, putting your feelings into words seems to regulate or dampen those feelings,鈥� says Lieberman.
