Ouch. This would hurt a lot less if it was an accident.

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Pain: 'Tis Better to Receive--Accidentally

When a teammate crashes into you playing soccer, you're likely to experience some pain. But if an opposing player hits you with the same amount of force, you'll hurt a lot more. That's the conclusion of a new study that finds that pain caused intentionally feels much worse than pain perceived as accidental.

While thinking about the debate over the torture of prisoners at Guantanamo Bay, psychologist Kurt Gray of Harvard University wondered whether the intent to deliver pain mattered. "Perhaps without this malicious intention, torture would not hurt as much," he says.

Gray and Harvard colleague Daniel Wegner tested the hypothesis on 43 student volunteers, most of them female. Each volunteer was paired with a partner, who, unbeknownst to the volunteer, was a part of the research team. The volunteers were asked to perform several tasks chosen by the partner from a pair of options. One of the choices was between gauging the pain of electric shocks delivered by a stimulator tied to the volunteer's wrist (on a scale of 1 to 7) and evaluating the relative pitch of different sounds. In one set of experiments, the partner selected the painful task whenever the shock or pitch choice came up; as a result, the volunteers felt that the partner was intentionally harming them. In the other set of experiments, the volunteers still received electric shocks, but they were told that the partner was not responsible.

As Gray suspected, intention mattered. Even though the intensity of the electric shock was the same throughout the experiment, the volunteers reported more pain (on average 5.64 out of 7) when they thought the partner was making them endure it on purpose than when the shock was not given knowingly (average 2.17). Moreover, when the volunteers felt that the shocks were unintentional, they got used to them, reporting less pain as time went on. Every "intentional" shock hurt as much as the first, however, because the malice of the intention kept it stinging, the authors reported 15 December in Psychological Science. These results, the team suggests, might help explain why torture is so difficult to endure--knowing that harm is intentional makes it even more painful.

Christopher Brown, a neuroscientist at Manchester University in the United Kingdom, calls the study a welcome step toward further understanding social effects on pain. He says he's curious about what effect these sorts of experiments have on the partner--versus on the volunteer. "I'd be excited to see future work looking at whether a person who is intentionally harming another experiences some kind of pain relief."