Researcher David Eagleman has tackled his very issue in a very clever way. He reasoned that when time seems to slow down in real life, our senses and cognition must somehow speed up-either that, or time dilation is merely an illusion. This is the riddle he set out to solve. "Does the experience of slow motion really happen," Eagleman says, "or does it only seem to have happened in retrospect?" To find out, he first needed a way to generate fear of sufficient intensity in his experimental subjects. Instead of skydiving, he found a thrill ride near the university campus called Suspended Catch Air Device, an open-air tower from which participants are dropped, upside down, into a net 150 feet below. There are no harnesses, no safety lines. Subject plummet in free fall for three seconds, then hit the net at 70 miles per hour.
Next, Eagleman outfitted his test subjects with a special device that he and his students had constructed. They called it the perceptual chronometer. It's a simple numeric display that straps to a user's wrist, with a knob on the side let the researchers adjust the rate at which the numbers flash. The idea was to dial up the speed of the flashing until it was just a bit too quick for the subject to read while looking at it in a non-stressed mental state. Eagleman reasoned that, if fear really does speed up our rate of perception, then once his subjects were in the terror of freefall, they should be able to make out the numbers on the display. As it turned out, they couldn't. That means that fear does not actually speed up our rate of perception or mental processing. Instead, it allows us to remember what we do experience in greater detail. Since our perception of time is based on the number of things we remember, fearful experiences thus seem to unfold more slowly.