Distortions of time can be common in healthy brains too, especially when seen in the rearview mirror.
Perhaps our best-known aphorisms about time perception are "time flies when you're having fun," and "a watched pot never boils." But when memory and emotion enter the picture, one neuroscientist found, both presumed truths get turned on their heads. Seen in hindsight, time slows down when you're in a state of great excitement; and looking back on the boredom of pot-watching, the absence of emotional peaks makes an incident seem as if it passed in an instant, says David Eagleman, a neuroscientist at Baylor College of Medicine in Texas.
In a series of daring -- and, he acknowledges, fun -- experiments, Eagleman and fellow researchers had 20 subjects winched up to the top of a 46-meter-tall tower at Dallas' Zero Gravity amusement park and then plunged safely into a net 31 meters below.
Eagleman knew that when calm, subjects were pretty accurate at timing the descent from the tower: When asked to estimate the length of airtime their compatriots experienced, their sober assessment was close to the mark: 2 1/2 seconds.
But Eagleton knew that in the wake of experiencing an emotionally arousing event -- a car crash, for instance -- most humans wildly overestimate its duration. To understand how such a distorted perception might come about, Eagleman needed to explore two possibilities:
First, at the time we experience an exciting event, do our hyper-alert senses take in more detail? And does that cause us -- at the time of the event -- to overestimate its duration in order to fit our enriched perception?
Or -- a second possibility -- does the time distortion of an exciting event come only later, when we reconstruct its overwhelming sensations? To accommodate so many arousing memories, do we overestimate the time it took for an event to play out?
To test the first possibility, Eagleman and his colleagues strapped hand-held computers to subjects' wrists as they experienced the terror (or thrill) of free fall. By having the subjects respond to several prompts on their speedy way down, experimenters measured whether the aroused subjects were actually taking in more information as they plummeted.
Results showed they were not. Effectively, subjects were accurately marking time on the way down.
But even though time was being accurately recorded during the plunge, memory seemed to play tricks with it later. To fit in all those remembered sensations, subjects would have to believe that an event must have lasted longer than it did, Eagleman surmised.
After subjects plunged from the tower, they obliged Eagleman. Asked to estimate the duration of their descents later, most guessed way too high.
"Time is a construction of the brain, and the brain goes through a lot of trouble to edit and present this story to you of what's going on out there and how fast or slowly it happens," Eagleman says. "But what your brain's telling you [that] you see is not always what's out there. It's trying to put together the best, most useful story of what's happening out there in the world."