11/03/2014 07:55 am ET Updated Jan 03, 2015

Law Enforcement and Deadly Decisions: What the Science Tells Us

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When unarmed people like Michael Brown, Eric Garner and Reeva Steenkamp are killed, we demand to know what impelled their killers to act. Were the armed men who killed them truly in fear for their lives, and if so why? Were these killings outright murders or reasonable self-defense? Our laws require answers to these questions, since the difference between self-defense, manslaughter, and murder can depend on the perpetrator's state of mind. But no matter how compelling these questions seem, these are the wrong ones to ask, because they don't really have answers.

Neuroscientists and psychologists now know that emotions and thought processes are created by incredibly complex biochemical feedback systems beyond our conscious awareness. Numerous studies have demonstrated that our brains determine a course of action up to 10 seconds before we become conscious of "our" decisions . Furthermore, at every moment we all have multiple thoughts, emotions, sensations, physical responses, and memories that impel us to act or inhibit action, most of which are beyond our awareness.

As Nobel-prize-winning psychologist Daniel Kahneman puts it in Thinking Fast and Slow, we have two decision-making capacities, fast and slow. The fast system makes most of our decisions most of the time. The fast system operates beyond our consciousness. The slow system is deliberate and is inoperable or offline when there are distractions, even those as minimal as walking. We can never know the instantaneous complex assessments that impel fast choices, which are largely governed by the unique historical interactions of our biology and environment.

Think, for example, about a decision as simple as whether to accelerate through a yellow light or step on the brakes. As you watch the light change, you probably hit one pedal or the other before you fully realize what you're going to do. Your decision will result from a morass of reflexes, responses, and beliefs, none of which you consciously think through before your foot moves: are you late? Did you see a police car out of the corner of your eye a few blocks back? What did the person you're talking to just say? How long do you think you have to clear the intersection? How did your parents teach you to drive? Are you tired, angry, or stressed? What are the vehicles around you doing? Are your levels of adrenalin, cortisol, testosterone, or estrogen elevated? All of these things and dozens more impact your choice, but you will never really know why you hit the gas (or didn't).

It would be comforting to think that life and death decisions are made more deliberately than traffic navigation, but this is not the case. Indeed, they are often at least as rushed and impulsive, with emotions running overwhelmingly high. If someone is terrified and holding a gun, or about to jump onto a subway platform to rescue a child, she is in a state of high arousal that impairs or precludes careful judgment.

A familiar high-intensity situation is having a terrific time on a date. Our excitement may prompt us to have sex without a condom or order another drink before driving home, despite our better judgment. Unless those choices lead to disaster, we may never stop to reflect on why we risked an STD or a fatal accident for a passing moment of pleasure.

According to Dr. Dan Ariely of Duke University, in Predictably Irrational, "we all systematically underpredict the degree to which [sexual] arousal completely negates our superego, and the way emotions can take control of our behavior." When we are in states of high arousal, our reactions are no longer rational or based on our conscious beliefs.

This is partly because we can't sense or control the neurochemical cascades occurring in our brains as we respond to events, though they produce most of the decisions we make every day. We are often a mystery even to ourselves -- just as we don't know why the thing that turns our friend on leaves us cold, we don't know why the situation that puts one person in fear for his life may leave another feeling almost unthreatened.

Indeed, most of us, in the moment, believe whatever we're doing is, if not the best thing to do, at least an acceptable thing to do, even when we take potentially lethal risks. Another reason why we make dangerous choices is captured by studies showing that people unconsciously tend to discount future losses in favor of present gains. (Kahneman and Ariely) The same unpredictable, reckless disregard for life and limb that propels us to homicides that may land us in jail, under different circumstances, leads to extreme acts of courage and heroism.

And afterwards, none of us can truly explain why. Indeed, we now know that when people give reasons for their behavior they are largely inventing rationalizations, because most mental processing is inaccessible to us. Therefore, efforts to determine whether the perpetrator of a killing was rational or felt seriously threatened are futile.

In most US states, laws regarding homicide require determination of two factors: the perpetrator's state of mind, and what was objectively reasonable in the situation. Knowledge of the former is unattainable. Knowledge of the latter can best be obtained through video evidence. The Ray Rice videos made it abundantly clear that video evidence can be powerful and revelatory, even in cases where the bare facts are not much in dispute. Best of all, modern technology has put it reliably within our grasp.

Indeed, there is now a trend among police departments across the nation to equip officers with wearable video cameras. The Justice Department concluded last month that this technology has the potential to "promote the perceived legitimacy and sense of procedural justice" in interactions between the public and law enforcement. It can also decrease the likelihood of unjustified homicides in the future.

Studies have demonstrated that the experience of being observed discourages impulsive and dishonest behavior. Even unconscious beliefs that we are being observed change behavior and make us more likely to exercise self-control.

Violent behavior by police is dramatically reduced when officers wear video cameras that record their actions. Interestingly, the police officers who have worn these cameras like them too, because they are protected against unfounded accusations.

Consequently, instead of relying on unknowable states of mind, we should rely on what modern technology now permits: video evidence. Everyone carrying a gun, including all law enforcement personnel, should be required to wear forward-facing cameras that actively record events. Failure to produce an unadulterated recording should also be a crime, and count in favor of the prosecution's case. This would give us objective information about whether the perpetrator's actions were in fact reasonable, and is likely to reduce both deaths and false accusations.

While one may say that we can't make such a demand of everyone, if we can insist that every driver carry a license and insurance to protect all of us from traffic accidents, we can also reasonably require that those who carry deadly weapons protect themselves and society more adequately from their own unknowable, unpredictable responses by ensuring that should the weapon be used, there will be actual evidence of how and why. Feeling endangered, without adequate video documentation, should no longer be an acceptable standard for self-defense for those with deadly weapons.