I once read a question that went as follows:

Two groups of young men are walking on opposite sides of the street. One group is black, the other, white. Both are loud and swaggering, both have baseball caps turned to the back, both are brandishing bats.

Which one is the baseball team and which one, the street gang?

The truth is, many of us — maybe most of us — would decide based on race, giving benefit of the doubt to the white group, leaping to the harshest conclusion with the black one. Some will resist that notion, but the reality of implicit bias has been exhaustively documented.

Dr. Angela Bahns, an assistant professor of psychology at Wellesley College who describes herself as a “prejudice researcher,” wanted to push the question further. Earlier this year she published a study testing what she says is the prevailing theory: Prejudice arises from threat, i.e., you perceive those other people over there as dangerous and that’s what makes you biased against them.

“My research,” she said in a recent interview, “tests whether the opposite is true, whether prejudice can precede and cause threat perception.” In other words, is it actually pre-existing bias that causes us to feel threatened? It’s a question with profound implications in a nation grappling with what has come to seem an endless cycle of police brutality against unarmed African-American men, women and children.

Reliably as the tides, people tell us race played no role in the choking of the man, the arrest of the woman, the shooting of the boy. But Bahns’ research tells a different story. She conditioned test subjects to feel negatively toward countries about which they’d previously had neutral feelings, including Guyana, Mauritania, Surinam and Eritrea. “And I found,” she said, “that when groups were associated with negative emotion, they came to be perceived as more threatening in the absence of any information about what the people are like objectively.”

This column, by the way, is for a woman named Tracy from Austin who wrote earlier this year to ask “What can I do?” to fight police brutality against African-American people. I promised her I would seek answers. Well, Bahns’ research suggests that one answer might be to encourage police departments to incorporate bias training in their regimens.

According to Bahns, this training can help people overcome implicit prejudice and the heightened perception of threat it brings, but there is an important caveat: They have to be motivated and willing and have to leave their defensiveness at the door. “Before any change can happen, the first step … is that the perceivers — in this case, the white perceivers, or police officers — have to be open to admitting that they might be influenced by bias. I think we’re not getting anywhere when there’s this defensive reaction. … We’re all prejudiced and until we admit that, we’re not going to get anywhere in terms of reducing its effects.”

Not that people’s defensiveness is difficult to understand. “Everyone’s motivated to see themselves in a positive light,” said Bahns. “..People that genuinely hold egalitarian values and desperately do not want to be prejudiced are very motivated not to see bias in themselves.”

The thing is, we cannot wait passively for their conundrum to resolve itself. Some of us are dying because of this inability to tell the ball club from the street gang. And frankly, if people really do hold egalitarian values and desperately don’t want to be prejudiced, those deaths should push them past defensiveness and on to reflection.

As Bahns put it, the idea “that threat causes prejudice assumes that something about them — the out group — makes them threatening rather than assuming there’s something about us that makes us see them that way.”

Leonard Pitts is a columnist for The Miami Herald. Contact him via e-mail at lpitts@miamiherald.com.