Want to Be Less Biased? Take a Nap

Outright racism and sexism may not be socially acceptable in many places, but long-held cultural beliefs about women and people of color still have a hold on society. Men are still more likely to be hired in the scientific world than women, even if their applications are otherwise identical. In lab tests, people are quicker to categorize black faces with “bad” words than good, and quicker to shoot black targets in video games. However, a study by Northwestern University psychologists published in 2015 found that people can be taught to shed some of their knee-jerk reactions toward women and people of color. But it helps if they take a nap. 

The researchers tested 40 men and women, all white, on their implicit assumptions of race and gender by showing them pictures of women and Black men. Each picture was accompanied by a word—for the gender test, art- and science-related words; for the race test, words denoting good and bad qualities. Initially, the participants expressed implicit social biases, showing a greater tendency to link women with artistic words (not scientific) and Black men with unpleasantness.

Then, participants went through anti-bias training. They were instructed to select only the picture-word pairs that went against the stereotype, linking women with science and Black men with goodness. Meanwhile, the scientists played specific sounds when the participants were shown correct (non-stereotypical) pairings, with one sound for the racial counter-bias pair, and one for the gender-related pair. Afterward, people showed decreased bias compared to their original baseline levels.

Later, the participants took a 90-minute nap. As they slept, the scientists played one of the two auditory cues. Once they woke up, the participants’ implicit biases were tested again. If they heard one of the cues during sleep, their implicit biases were significantly reduced compared to before sleeping. Those who didn’t hear the cue sound didn’t exhibit any change in implicit bias between going to sleep and waking up. A week later, those who heard the cues during sleep retained their bias reduction.

Previous research by some of the same psychologists found that, in general, sleeping helps reinforce memories of what you’ve already learned. Apparently, this applies to more than just learning facts. 

“Biases can operate even when we have the conscious intention to avoid them,” co-author Galen Bodenhausen explained in a press statement. Even well-intentioned people exhibit racial and gender biases, which are often reinforced by portrayals in media. Anti-bias training could help people shed some of those unconscious associations. 

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A version of this story ran in 2015; it has been updated for 2024.