Watching how black characters are treated on television can affect attitudes about race both consciously and unconsciously, new findings suggest. In a two-part study, researchers at Tufts University examined nonverbal behavior toward characters of different races on television shows, then tested how clips from these shows affected viewers’ prejudices.

First, the team found clips of mixed-race scenes from 11 popular TV shows with prominent black and white characters. In each clip, they blocked out one character to hide his or her race, turned off the sound, then asked volunteers whether the blocked-out character was seen by the other characters in a positive or negative light. The researchers found that in nine of the 11 shows—Friday Night Lights, CSI, House, CSI: Miami, Scrubs, Greek, Heroes, Reno 911! and Grey’s Anatomy—viewers thought the actors’ body language and facial expressions were less favorable when they were responding to someone who was black. The only two shows without this bias were Bones and Rob and Big.

Then the researchers showed clips from all the shows, with the images restored to normal, to a new group of viewers who had no idea the study was about race. After watching clips in which black characters were treated less favorably than whites, the viewers’ conscious attitudes about race did not change. But they were faster to associate white people with positive words such as “laughter” and black people with negative words such as “failure”—a sign that this implicit bias had found its way from the TV screen into people’s behavior, the researchers say. After watching clips in which black characters were treated better than whites, however, viewers not only displayed less implicit bias toward blacks, they also showed improved conscious attitudes toward blacks as measured by a questionnaire.

Because these TV shows’ bias in either direction is unintentional, suggests Tufts psychologist Nalini Ambady, one of the researchers working on the study, simply being aware of it might help actors and directors to counteract it or use it to a positive end.