Although most white Americans self-report little to no racial bias against black people, they tend to show robust implicit, or unconscious, biases.

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NEXT year marks the 50th anniversary of the U.S. Supreme Court ruling that found laws banning interracial marriage to be unconstitutional. Although polls indicate that acceptance of interracial marriage has increased dramatically since then, incidents of prejudice and violence against interracial couples continue.

In April, a Mississippi landlord evicted a family after he found out the couple was interracial. Then in August, a man stabbed an interracial couple in Olympia after seeing them kiss in public.

As a social psychologist, I wondered if these types of incidents are aberrations or indications of a persistent underlying bias against interracial couples.

To test this, my colleague Caitlin Hudac and I designed a series of studies to examine people’s deep-seated feelings about interracial relationships.

Through the early 20th century, many Americans reacted to the idea of interracial marriage with revulsion. Although attitudes have supposedly changed, a 2013 column by The Washington Post’s Richard Cohen suggests that some still feel disgusted by interracial relationships. This disgust is the feeling we decided to zero in on.

We first asked a predominantly white sample of college students how disgusted they feel by relationships between blacks and whites and how accepting they were of them. Consistent with polls, participants claimed to be largely accepting of interracial relationships. We found that the less accepting people were of such relationships, the more disgusted they were by them.

However, the problem with asking people to self-report their attitudes about sensitive topics is that they are often unaware or unwilling to report their own biases. Although most white Americans self-report little to no racial bias against black people, they tend to show robust implicit or unconscious biases.

To get around that, we next measured participants’ brain activity, recording the brain waves of a predominantly white sample of college students while they viewed 100 images of black-and-white interracial couples and an equal number of same-race couples (both black and white).

We wanted to see what would happen in the insula, an area of the brain activated when people feel disgusted. Overall, viewing interracial couples increased insula activation — participants showed more activation when looking at interracial couples than same-race couples. Although the insula is not exclusively linked to disgust, taken with the results of our first study, these findings suggest that people feel increased disgust when viewing interracial couples.

Our final study looked at the ramifications of feeling disgusted by interracial couples. Research shows that feeling disgusted by others often leads us to dehumanize them. So we wondered whether disgust about interracial couples might lead people to dehumanize them. We recruited another predominantly white sample of college students and divided them into two groups. One was induced to experience disgust through being shown a series of disgusting images — which was expected to make them more likely to dehumanize interracial couples. The other group was used as a control.

Next, we had participants complete an implicit association test. Such tests are used to gauge unconscious associations by asking people to make split-second categorizations. We asked participants to quickly categorize images of interracial couples, same-race couples, silhouettes of humans and silhouettes of animals. The silhouettes were intended to represent “humanization” and “dehumanization,” respectively.

We predicted that when interracial couples and animals were categorized together, the participants who were primed to feel disgusted would do the task faster. Instead, we found that all participants completed the task faster when interracial couples and animals were categorized using the same button (indicating implicit dehumanization). However, participants who were primed to feel disgusted were able to do it the fastest.

Overall, our research suggests that when it comes to interracial relationships, polls don’t tell the whole story. Interracial couples still elicit disgust in many people, which can translate into dehumanization. These biases evidence deeply ingrained societal attitudes about race in our culture — but there is a new and growing field of research on methods to reduce these biases.

Although our research cannot speak directly to the consequences of dehumanizing interracial couples, the implications are startling. Dehumanizing people eliminates the burden of empathizing with them. And at its most extreme, dehumanization can lead to acts of violence and cruelty — like the stabbing this summer in Olympia.