Starbucks, trying to put to rest an outcry over the arrest of two black men at one of its stores, is closing more than 8,000 stores for an afternoon of anti-bias training, a strategy some believe can keep racism at bay.

After the arrests in Philadelphia last month, the coffee chain's leaders apologized and met with the two men, but also reached out to activists and experts in bias training to put together a curriculum for its 175,000 workers.

That has put a spotlight on the little-known world of "unconscious bias training," which is used by many corporations, police departments and other organizations to help address racism in the workplace. The training is typically designed to get people to open up about implicit biases and stereotypes in encountering people of color, gender or other identities.

Get Breaking News Delivered to Your Inbox

The Perception Institute, a consortium of researchers consulting with Starbucks, defines implicit bias as attitudes — positive or negative — or stereotypes someone has toward a person or group without being conscious of it. A common example, according to some of its studies, is a tendency for white people to unknowingly associate black people with criminal behavior.

Many retailers including Walmart and Target said they already offer some racial bias training. Target says it plans to expand that training. Nordstrom has said it plans to enhance its training after issuing an apology to three black teenagers in Missouri who employees falsely accused of shoplifting.

Anti-bias sessions can incorporate personal reflections, explorations of feelings and mental exercises. But one expert says training of this kind can have the opposite effect if people feel judged.

According to a video previewing the Starbucks training, there will be recorded remarks from Starbucks executives and rapper/activist Common. From there, employees will "move into a real and honest exploration of bias" where, in small groups, they can share how the issue comes up in their daily work life.

Starbucks has described it as a "collaborative and engaging experience for store partners to learn together." "

Developed with feedback from the NAACP Legal Defense and Education Fund, the Perception Institute and other social advocacy groups, the four-hour session will give workers a primer on the history of civil rights from the 1960s to present day. Workers will also view a short documentary film.

Alexis McGill Johnson, Perception's co-founder and executive director, says anti-bias training is about awareness.

"The work that we want to do is not say you're a bad person because you have a stereotype about a group, but say this is why your brain may have these stereotypes," she said.

Johnson declined to elaborate on the details of the Starbucks training. But she said Perception's workshops typically include mental exercises to show participants how bias creeps into situations. A session can include personal reflections, she said, such as, "'I was socialized to think about a group this way.'"

Johnson said the real work is for employees to apply what they learn in their everyday lives. She likened it to exercising a muscle. Some ways to practice counter-stereotyping, she said, are to look for something unique about a person that is beyond their social identity.

"It could be having a question that elicits something more interesting than, say, the weather or the traffic," Johnson said, stressing the need to "go well beyond the superficial."

In the Philadelphia incident, Rashon Nelson and Donte Robinson were asked to leave after one was denied access to the bathroom. They were arrested by police minutes after they sat down to await a business meeting. The incident was recorded by cellphones and went viral.

Nelson and Robinson settled with Starbucks this month for an undisclosed sum and an offer of a free education. They also reached a deal with the city of Philadelphia for a symbolic $1 each and a promise from officials to establish a $200,000 program for young entrepreneurs.

Starbucks has since announced anyone can use its restrooms even if they are not buying anything. According to documents Starbucks sent to store workers, employees should also think carefully when dealing with disruptive customers. A guide advises staff to consider whether the actions they take would apply to any customer in the same situation. They should dial 911 only if the situation seems unsafe.

Starbucks said the arrests never should have occurred and announced the mass closures of its stores for the afternoon of training.

Calvin Lai, an assistant professor of psychological and brain sciences at Washington University in St. Louis, said people should not place high expectations on this one day.

"We find that oftentimes diversity training has mixed effects, and in some cases it can even backfire and lead people who are kind of already reactive to these issues to become even more polarized," Lai said.

One afternoon wouldn't really be "moving the needle on the biases," especially when it's a company with as many employees as Starbucks, he said. "A lot of those employees won't be here next year or two years or three years down the line."

Starbucks has said Tuesday's sessions serve as "a step in a long-term journey to make Starbucks even more welcoming and safe for all." It is working with volunteer advisers including Heather McGhee, president of social advocacy organization Demos, and Sherrilyn Ifill, president and director-counsel of the NAACP Legal Defense Fund.

"One of the things Starbucks has to wrestle with is how to incorporate this kind of training into the onboarding of every employee," Ifill said.

That takes a sustained effort, McGhee added.

"We have really made it clear that one training is not enough, and this needs to be part of an ongoing review of their policies," McGhee said. "They really need to commit."