The sight was not that unusual, at least not for Mosul, Iraq, on a summer morning: a car parked on the sidewalk, facing opposite traffic, its windows rolled up tight. Two young boys stared out the back window, kindergarten age maybe, their faces leaning together as if to share a whisper.
The soldier patrolling closest to the car stopped. It had to be hot in there; it was 120 degrees outside. "Permission to approach, sir, to give them some water," the soldier said to Sgt. First Class Edward Tierney, who led the nine-man patrol that morning.
"I said no — no," Sergeant Tierney said in a telephone interview from Afghanistan. He said he had an urge to move back before he knew why: "My body suddenly got cooler; you know, that danger feeling."
The United States military has spent billions on hardware, like signal jamming technology, to detect and destroy what the military calls improvised explosive devices, or I.E.D.'s, the roadside bombs that have proved to be the greatest threat in Iraq and now in Afghanistan, where Sergeant Tierney is training soldiers to foil bomb attacks.
Still, high-tech gear, while helping to reduce casualties, remains a mere supplement to the most sensitive detection system of all — the human brain. Troops on the ground, using only their senses and experience, are responsible for foiling many I.E.D. attacks, and, like Sergeant Tierney, they often cite a gut feeling or a hunch as their first clue.
Everyone has hunches — about friends' motives, about the stock market, about when to fold a hand of poker and when to hold it. But United States troops are now at the center of a large effort to understand how it is that in a life-or-death situation, some people's brains can sense danger and act on it well before others' do.
Experience matters, of course: if you have seen something before, you are more likely to anticipate it the next time. And yet, recent research suggests that something else is at work, too.
Small differences in how the brain processes images, how well it reads emotions and how it manages surges in stress hormones help explain why some people sense imminent danger before most others do.[...]