Scientists have long known that sleep boosts the brain, helping us consolidate memories and learn new things.
Now, a provocative new study shows it may even have the power to help us reverse deeply rooted stereotypes against women and African-Americans -- a finding which has important implications given the state of race relations in America, and the gender gap in math and science.
“These biases are well-learned," Dr. Xiaoqing Hu, a postdoctoral researcher at the University of Texas at Austin and lead author of the study, told The Guardian. "They can operate efficiently even when we have the good intention to avoid such biases. Moreover, we are often not aware of their influences on our behavior."
Disturbing biases measured. For the study, the researchers recruited 40 white men and women between the ages of 18 and 30 and had them complete a task called the Implicit Association Test (IAT), which measured their baseline gender and racial biases.
Then, the participants completed two "counter-stereotype trainings," which involved looking at different faces -- black and white, male and female -- paired with words on a computer screen (see diagram).
The participants were asked to press a button labeled "correct" when female faces appeared next to science and math words, and when black faces were paired with positive words like "cheer, smile, or honor."
When the participants identified these pairings quickly and accurately, two specific sounds were played -- one sound for the "women-science" pairing, and one for the "black-good" pairing.
Just a few zzz's. After the training, the participants took a 90-minute-long nap. Once they fell into a deep sleep, the researchers played one of the two sounds repeatedly. When the participants woke up, they took the IAT again.
What happened? Participants' biases fell by more than 50 percent for the bias associated with the sound they heard while asleep. For instance, if participants heard only the "women-science" sound, their gender bias was reduced -- but their racial bias stayed the same.
The participants were tested again a week later, and they continued to be less biased -- although at a lower rate of around 20 percent, according to Hu.
"It is somewhat surprising that the sleep-based intervention could have an impact that was still apparent one week later," Hu said in a written statement. "The usual expectation is that a brief, one-time intervention is not strong enough to have a lasting influence."
In the real world. Hu and her colleagues think these interventions could be applied to reduce other biases too, such as those related to religious affiliation, sexual orientation, political preference, weight, and disability. But more research is needed to find out whether these interventions can change behavior in the real world.
"We didn't have people interact with or make decisions about other people, so that sort of experiment is needed to know the full effects of the methods we used," Dr. Ken Paller, director of the cognitive neuroscience program at Northwestern University and one of the researchers, told BBC News. "But we suggest that modifying unconscious social bias is likely to influence the extent to which decisions are influenced by racist or sexist attitudes."
He added that if the interventions can affect decision-makers, it raises the question of "whether people in positions of authority in society, such as judges and police officers, and perhaps people who make hiring decisions, should have their unconscious bias evaluated and perhaps trained to some standard."
Unethical tampering? Scientists who were not involved in the research find the study's results encouraging, but some believe that conducting such experiments while the participant is asleep also raises ethical concerns.
As Dr. Gordon Feld and Dr. Jan Born, psychologists at the University of Tubingen in Germany, wrote in a commentary on the study, it involves tampering with people while they are in "a state... without willful consciousness and therefore vulnerable to suggestion."
The commentary and the study were published on May 29, 2015 in the journal Science.
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