While researchers say the experiment was much less complex than real-life encounters, they hope it begins to shed light on how subtle racial biases may help lead to situations in which police accidentally shoot unarmed minorities.
"People don't have to be bigots to be under the influence of racial bias, at least in some conditions like the time pressures we had in these experiments," said Keith Payne, co-author of the study and assistant professor of psychology at Ohio State University.
Payne and his colleagues conducted two related experiments in which white and Asian Americans viewed on a computer screen a picture of a man, quickly followed by a picture of a either a tool or a gun. Both pictures were visible for only about a fifth of a second each.
When asked to identify – within less than one second -- whether the second picture was a tool or a gun, participants were much more likely to misidentify a tool as a gun when the preceding picture was that of an African American.
They were more likely to misidentify a gun as a tool when the preceding picture was that of a white man.
But when they were given time after their response to reconsider their identifications, the participants almost always were able to correct their errors, Payne said.
The results show how unconscious bias against blacks may affect decision-making in cases of extreme time pressure, Payne said. The reason, at least in these experiments, has to do with failures to control bias under time pressure, not distorted perceptions of what's being seen.
"In these experiments, people knew the correct response, but when they had to make snap judgments they were sometimes swayed by unconscious bias," Payne said. "When they had enough time, they could almost always report correctly whether they were seeing a gun or a tool."
Payne conducted the study with Yujiro Shimizu and Larry Jacoby of Washington University in St. Louis. Their results will be published in an upcoming issue of the Journal of Experimental Social Psychology.
In the first study, 33 college students were shown a series of photos: first a photo of a face, followed by either a tool or a gun. Participants were more likely to misidentify a tool as a gun when they saw the black face, and misidentify a gun as a tool when they saw a white face.
However, after each combination of face and tool or gun, the participants were asked to rate on a scale of 1 to 6 how confident they were in the answer they just gave. When participants made misidentifications, they almost always expressed low confidence in their answers. When correct, they almost always expressed high confidence.
The second study was nearly identical except that, instead of expressing confidence in their answers, 33 new participants were given the opportunity to change their answer, without time pressure.
In this case, participants falsely said tools associated with black faces were guns about 15 percent of the time. But when they were given a second chance to respond, they made the same error less than 2 percent of the time. They falsely said tools associated with white faces were guns about 11 percent of the time, which dropped to about 3 percent on second response.
Guns were more likely to be called tools when associated with white faces, rather than black faces, at first response, but those errors were nearly always corrected during the second response.
Although the difference between "false positive" gun reports for black and white faces seems relatively small (4 percent) in this experiment, Payne said the percentage is somewhat arbitrary -- the difference increases as time pressure increases. In experiments where people are asked to respond even more quickly than in this study, the difference has grown to 10 percent.
Earlier studies by Payne and his colleagues, and other researchers, had also found evidence of this unconscious racial bias in identifying weapons.
But Payne said this study goes further by showing how this racial bias comes about. The two most likely reasons would be that misidentifications result from distorted perceptions of what is being seen, or that they result from failures to control one's responses.
The results from these studies suggest that it is the second explanation – a failure to control unconscious biases – that is most likely, at least in this situation. The fact that participants were able to correct their errors when given enough time suggests that they did not have distorted perceptions of what they saw – they could see the difference between the gun and the tool.
"Even though it was perfectly clear to the participants what they saw and what they should do, that knowledge broke down under the time pressures and racial bias influenced their answers – despite their best intentions," Payne said.
"It's a bit like being tongue-tied. You know what you want to say, but the words don't come out right."
Real-life situations in which police officers have to decide whether a suspect is holding a weapon are much more complex than this experiment, Payne said. For one, participants in this study could see clearly whether the object was a gun or tool. Police may not have that luxury. In these cases, distorted perceptions may also play a role in misidentifications of weapons.
But Payne said the study shows how all people – police officers especially – need to be especially vigilant about how they react when under stresses such as extreme time pressure.
"It's when they are under stresses such as time pressure that control tends to break down and things like racial bias can play a stronger role in our actions," he said.
Journal of Experimental Social Psychology