Participants in a new study of the use of police deadly force were more willing pull the trigger on armed white suspects than on blacks, researchers have found.

The surprising results challenge previous findings about racial bias - and, one the researchers says, helps combat the stereotype that cops are more eager to open fire on black suspects.

The authors of the study say the reaction delay is because officers fear that there will be greater repercussions from shooting a black suspect than a white one.

The study, conducted at Washington State University-Spokane's Sleep and Performance Research Center, used a realistic simulator that showed video images of black, white and Hispanic suspects - both armed and unarmed. Participants were given a real Glock pistol equipped with a laser and told to shoot armed attackers.

The study tested more than 30 cops, as well as 60 civilians and a half-dozen members of the military. About 85percent of the study participants were white.

Realistic: A study that put participants in a simulator and had them shoot at armed suspects found that they were more hesitant to pull the trigger on blacks than on whites

The study armed participants with a real Glock pistol that fired lasers instead of bullets - and measured the reaction times and accuracy

When confronted with an armed white suspect, participants took an average of 1.37 seconds to pull the trigger. But, they took 1.61 seconds to open fire on armed black suspects - and were less likely to shoot unarmed targets.

That split-second pause could be deadly in a real life situation, researchers say.

Moreover, the study also monitored physiological responses to the shooting scenarios and found that shooters paused - despite participants perceiving the black suspects as being a bigger threat than the white suspects.

The study contradicts previous findings that people were more likely to pull the trigger on black suspects

Lois James, a Washington State University-Spokane professor, was lead author on the study

The results were consistent for police officers, as well as civilians and members of the military, Lois James, assistant research professor at Washington State University-Spokane, told Daily Mail Online.

'What it suggests that when faced with black suspects, there is something going on that is making some kind of pause or hesitation. What we think it might be is the fear of consequence,' Dr James said.

Dr James said those consequences could be moral - or they could be fear of backlash, either public brouhaha, criminal charges or departmental discipline.

'There's a history systemic racism in the US and there are still irrefutable facts about the treatment of some groups of people in the criminal justice system that I'm sure weigh very heavily on a lot of officers,' she said.

Dr James conceded that it is possible that the participants in the study knew that they were being watched by researchers and delayed opening fire on black suspects as a result.

However, she says researchers worked to minimize that bias. The study was initially designed to test how fatigue, experience and other factors impact in decision-making in deadly force scenarios and so race was never mentioned with participants before they went through the course.

Additionally - Dr James says - the simulator offers realistic scenarios that show life-size videos of police traffic stops and other incidents. The set-up means that most participants have very real physiological and psychological reactions to what's unfolding in front of them, she says.

Previous studies that showed a people had a bias toward using force against black suspects used much less immersive techniques - having participants sit in front of a computer screen and push a 'shoot' or 'don't shoot' button in response to pictures of armed suspects.

The findings, co-authored by David Klinger, a criminal justice professor at the University of Missouri-St. Louis, and Washington State University-Spokane professor Bryan Vila, were published in May in the Journal of Experimental Criminology.