Research shows key role for unconscious bias

That means that people who are not racist may unknowingly behave in ways that reflect racial stereotypes, even when they may disagree with such ideas. One study found that doctors with more unconscious bias against blacks were less likely to give African-American heart attack patients clot-busting medication than white patients. Another found that when participants in a computer simulation were told to shoot criminals but not unarmed citizens or police who appeared on the screen, more black than white men were incorrectly shot. Other work found that children perceived ambiguous, but aggressive behavior as more threatening if the perpetrator was black.

It’s impossible to know whether hidden bias caused Cambridge police Sergeant James M. Crowley, a white man who teaches courses on how to avoid racial profiling, to arrest the African-American Gates. But research indicates that a large majority of white people, and about half of black people, are quicker to make positive associations with white people and negative associations with black people.

“I think our data, obtained from millions and millions of people, show a real disparity between who we think we are, who we say we are . . . and what actually goes on in our heads,’’ said Mahzarin R. Banaji, a Harvard psychology professor who is a leader in studying such implicit bias.

Banaji’s research has found, for example, that many white people more quickly associate positive adjectives with white faces and negative adjectives with black faces. In computerized tests, many white people also more quickly associate harmful weapons with black faces than with white ones.

Overall, Banaji said, about 75 percent of white people show a white preference in such lab experiments, whereas black people are split half and half between favoring black and white.

That means that while the incident in Cambridge two weeks ago has layers of complexity and confusion, a vast body of scientific literature suggests the important role that unconscious bias would probably play.

“We don’t have the control condition; we don’t have exactly the same thing happening at the same time in which we replace Skip Gates with, say, [Harvard president] Drew Faust,’’ Banaji said, adding that in that case, “It is very hard to imagine things would have gone the way they did.’’

The unconscious attitudes that people carry with them are thought to be learned early in life. Studies have examined the origins of the “other race effect,’’ for example, a bias in which people have more trouble telling the difference between faces of people of another race and found that African babies raised in Caucasian families do not favor their own race, unlike babies raised in their own racial environment.

The formation of such deeply rooted biases probably served a specific purpose during evolution, said David Amodio, a psychology professor at New York University.

“These initial gut reactions - they’re built into evolutionarily old parts of our brains as mechanisms for survival,’’ Amodio said. “You need to be able to react really quickly to something that’s a potential threat, and in our evolutionary past, people didn’t have interactions across groups as much.’’

Given that such reactions may be deeply embedded in our brains, there is no sure way to erase them, but Amodio said the frontal cortex, the part of the brain that is goal-oriented, can keep the brain on task to overcome implicit bias when there is a clear procedure, in a law enforcement situation, for example, having an encounter guided by a protocol.

Dr. Alexander R. Green, associate director for the disparities solutions center at Massachusetts General Hospital, has studied racism in the medical context, finding that implicit biases due to race can affect the way people care for their patients. He said the first step in combating such bias is to be aware that it exists.

“We cannot necessarily change our unconscious biases,’’ Green said. “Many of these are deeply ingrained and not our intention. We can recognize how they come into play and try to consciously override them.’’

Another way of dealing with such situations may just be to increase exposure to people of diverse backgrounds. A study by Brown University and University of Victoria researchers published this year found that it was possible to reduce one measure of implicit racial bias, simply by giving people training that allows them to help tell faces of people from other races apart, which could allow them to see people as individuals, rather than a group.

Reducing implicit racism is something that Banaji thinks will take more than just a racial profiling class or a series of lectures, however. Like patients with cardiovascular disease who change their lifestyle completely, “unlearning’’ unconscious racism will require systemic change and a new understanding that everything, from portrayals of race in the media to the friends we hang out with, influence our unconscious biases and that our choices affect our biases.

“I can decide, what do I want to teach my brain?’’ Banaji said.

Carolyn Y. Johnson can be reached at cjohnson@globe.com.