The Brain Likes Categories. Where Should It Put Mixed-Race People?

Humans like to place things in categories and can struggle when things can't easily be categorized. That also applies to people, a study finds, and the brain's visual biases may play a role in perceptions of mixed-race people.

The study, published in Psychological Science on Monday, asked people to sort images of people as either white or black, but it included multiracial faces in the mix, too. There has been much less research into attitudes about mixed-race people, even though they are the fastest-growing racial group in the United States.

The 235 study participants, who all self-identified as white, signed up through the online survey site Mechanical Turk and provided their ZIP codes. The researchers then used U.S. Census data to determine their level of exposure to other racial groups.

People who lived in areas with more racial diversity categorized the faces with less hesitation, according to analysis of the participants' use of a computer mouse during the experiment.

The researchers say that by using mouse tracking they were able to get a clearer sense of the participants' reactions, unlike other studies of unconscious racial bias that have relied on surveys where participants could change or correct their answers. The mouse movements of those who lived in less racially diverse areas meandered more between the two choices before picking one.

"Where you live influences how easily you process biracial faces which may, without your awareness, be affecting your attitudes toward them," according to Diana Sanchez, an associate professor of psychology at Rutgers and an author of the study.

The researchers then asked a second group of 148 people to rank images of white, black and mixed-race faces for trustworthiness. The participants all identified themselves as white. Those who had more exposure to mixed-race people in real life were less likely to categorize them as untrustworthy.

Some of the bias could be explained not just by lack of familiarity, but by the brain's insistence on putting people into rigid categories, according to Jonathan Freeman, an assistant professor in New York University's department of psychology who was lead author of the study. "Some portion of the bias in certain cases can be explained from the way we visually experience other individuals."

In other words, in some measure it's literally an issue of perception.