DOUBT VS BENEFIT:

In 2002, a study by Joshua Correll and colleagues called "The Police Officer's Dilemma" was published. In the study, researchers reported that they presented photos of black and white men holding either a gun or a non-threatening object (like a wallet) in a video game-style setting. Participants were asked to make a rapid decision to "shoot" or "don't shoot" each of the men based on whether  the target was armed. 

They found that people hesitated longer to shoot an armed white target (and they were more likely to accidentally not shoot). Participants were quicker and more accurate with black armed targets but there were more "false alarms" (shooting them when they were unarmed). These effects were present even though participants did not hold any explicit discriminatory views and claimed that they wanted to treat all targets fairly.

The effect we see here is a subconscious but measurable preference to give white men the benefit of the doubt in these ambiguous situations. Decision times can vary by a fraction of a second, but that fraction can mean life or death for the person on the other end of the gun.

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