Can gender and racial biases be unlearned during sleep?

Even when we're not conscious of it, stereotypes and implicit biases about race and gender can affect the way we view and respond to other people -- and how they view us. Now a new study suggests it may be possible to alter or reduce those biases while we sleep.

Researchers from Northwestern University examined whether playing auditory cues during sleep could alter people's reactions toward others.

Previous research has shown that common social stereotypes, even subconscious ones, can have negative consequences in everyday life. One study found that employers were less likely to hire women for math jobs even when they were equally qualified as their male counterparts. Another found that while playing a video game, when participants were told to shoot only people carrying weapons, they were more likely to shoot unarmed black targets as opposed to those who were white. (This occurred whether the person being tested was black or white themselves.)

In the current study, published in Science, the authors wanted to test if they could alter these implicit biases using conditioning exercises during sleep. Forty participants in the experiment completed two training exercises, one designed to counter racial bias and the other gender bias. In the first task, images of females appeared on a computer screen with words that counter gender stereotypes, like math and science terms. Pictures of black individuals were paired with positive words. Two distinctive sounds also played during each image-word pairing, creating a strong association between the sounds and the pairs.

After the exercise, the participants took a 90-minute nap. While they were in deep sleep, the researchers played one of the sounds repeatedly, but not loud enough to disturb sleep.

The results showed that the implicit biases among the participants were reduced when compared to a baseline measurement before the training exercise and nap. The change even held up when they were tested again one week later, though the association was weaker.

Xiaoqing Hu, who led the study, was surprised by this lasting result. "The usual expectation is that a brief, one-time intervention is not strong enough to have a lasting influence," he said in a statement. However, Hu acknowledged in the study that further research is needed to address how much training is needed to produce long-term effects in implicit bias reduction and if it could have explicit benefits in real-life interactions. "It might be better to use repeated sessions and more extensive training," he said. "But our results show how learning, even this type of learning, depends on sleep."

Researchers explain that this is possible because prior research shows memories can be reactivated during sleep. "We call this Targeted Memory Reactivation, because the sounds played during sleep could produce relatively better memory for information cued during sleep compared to information not cued during sleep," said Ken Paller, senior author of the study and professor of psychology at Northwestern's Weinberg College of Arts and Sciences. This training has been studied in the past to help improve spatial memory, such as learning the locations of objects, and skill memory, like learning to play an instrument or speak a new language.

Paller also noted that the study could have implications for reducing other kinds of unwanted social biases and even may help reduce bad habits, such as smoking, self-centeredness, phobias, or unhealthy eating behaviors.

In an accompanying editorial, two other psychologists, Gordon Feld and Jan Born, caution that this type of research needs to be guided with much ethical consideration. "Sleep is a state in which the individual is without willful consciousness and therefore vulnerable to suggestion," they write.

Beyond that, they say that the study's findings "highlight the breadth of possible applications to permanently modify any unwanted behavior by targeted memory reactivation during sleep."