Prejudices tend to lurk in our unconscious minds. Few Americans would admit to holding stereotyped views of blacks or women, but tests designed to measure underlying thought patterns suggest the presence of buried biases that still influence our opinions and behavior.

The good news is these harmful assumptions are learned, and they can be unlearned. Newly published research suggests such biases can be diminished with the help of the simplest and most natural process imaginable: Sleep.

A research team led by psychologists Ken Paller of Northwestern University and Xiaoqing Hu of the University of Texas-Austin reports it was able to able to reduce prejudice through a combination of conscious brain training and subliminal reinforcement as the study participants napped.

That latter component is essential to the process, the researchers report in the journal Science. Sleep, after all, is where learning really sinks in, as memories are consolidated. It appears the same is true for unlearning prejudicial assumptions.

Their experiment featured 40 members of the Northwestern University community, who began by taking two versions of the Implicit Association Test. One “examined the degree to which female faces were preferentially associated with art vs. science words,” while the other “examined the degree to which black faces were preferentially associated with bad vs. good words.”

Sleep, after all, is where learning really sinks in, as memories are consolidated. It appears the same is true for unlearning prejudicial assumptions.

As expected, the results found participants “held implicit social biases for both gender and race.”

They then participated in a second task, in which they “viewed several types of face-word pairings, but were required to attend and respond only to pairings that countered the typical bias.” Each time they did so correctly, they heard one of two “unusual frequency-modulated sounds.”

Participants then took the Implicit Association Test a second time; their scores reflected lower levels of unconscious prejudice. Afterwards, all were “invited to take a 90-minute afternoon nap.”

“When electroencephalographic signals showed clear signs of slow-wave sleep (that is, non-REM sleep),” the researchers write, “we repeatedly played one auditory cue”—either the sound that was associated with a lack of gender bias, or the one associated with a lack of racial bias.

Upon awakening, participants took the IAT again, with encouraging results: The type of implicit bias related to the sound they heard while sleeping “was significantly reduced from pre-nap to post-nap.” In contrast, levels of the other type of bias remained unchanged.

One week later, the participants returned to the lab and took the IAT one final time. The results showed that levels of the prejudice associated with the nap-time sound remained at the reduced, immediate post-nap level. In contrast, the other bias increased over the course of the week.

In other words, the mental training intended to override deep-seated cultural biases only took hold if it was reinforced during sleep. Without that reinforcement, “training events tended to dissipate, and the bias returned to baseline levels,” the researchers write.

Granted, the process they describe has the potential for abuse. In an accompanying editorial, Gordon Feld and Jan Born of the University of Tuebingen note that it is reminiscent of Aldous Huxley’s Brave New World, “where young children are conditioned to certain values during sleep.” They caution that any widespread application of these principles “needs to be guided by ethical considerations.”

True enough. But it needs to be noted that the study participants were consciously involved in the anti-bias training, and presumably wished to be cleared of such prejudices. It’s not clear whether the process would have the same results if it was used in an attempt to override someone’s will.

Also, keep in mind that a very similar process occurs naturally—only with less-desirable results. In a separate study just published in Psychological Science, a University of Texas-El Paso research team demonstrates that prejudice against an outside group consolidates in our brains over time.

Specifically, it found after a group of Latinos were given negative information about African-Americans, their implicit anti-black prejudice increased “only after a 48-hour delay.” It takes time—and, presumably, sleep—for such information to be consolidated into one’s unconscious thought process.

So this sort of “programming” is already happening to us, every time someone repeats a stereotypical comment about a group of people. In this hopeful study, Hu, Paller, and their colleagues demonstrate that this process can be manipulated so as to open our minds rather than close them.

Findings is a daily column by Pacific Standard staff writer Tom Jacobs, who scours the psychological-research journals to discover new insights into human behavior, ranging from the origins of our political beliefs to the cultivation of creativity.