A few moments ago, I was strapped into a harness and winched 150 feet into the air. Four massive steel girders support my weight, and I can see that I’m the highest object around for miles. I am about to become the fastest-moving man in science, and I can barely keep my breakfast down.
This contraption is called the Suspended Catch Air Device, but the folks at the Zero Gravity Thrill Amusement Park in Dallas prefer the more colloquial “Nothin’ But Net.” That’s because when the operator releases my rope, I will fall, untethered, until I plop into a modified circus net. The terrifying free fall will last less than three seconds, but to me it will feel much longer. And in this experiment, that is exactly the point.
The study of how the brain perceives the passage of time is no longer just the work of philosophers. In the past few decades, medical scanners and computers have improved such that scientists can monitor the brain’s activity millisecond by millisecond. Sorting out how the brain handles time-related information could reveal the cause of several mental illnesses. But some basic information still eludes researchers, in particular an explanation for “time dilation,” the notion that time seems to slow during life-threatening situations. My impending fall is the latest in a series of experiments designed by David Eagleman, a neuroscientist at Baylor College of Medicine, to crack this nut.
Attached to my wrist is a perceptual chronometer, basically two LED screens, each blinking random digits between 1 and 9. Before I was hoisted up here, the chronometer was set so that the numbers alternate just fast enough that I cannot read them. If Eagleman is correct, and the brain’s perception of time slows down during disaster, then I should see the numbers on the chronometer flicker in a readable slow-mo, sort of like how characters in The Matrix films see bullets. That is, if I can keep my eyes open.
In recent years, scientists have learned that the circadian rhythms that control our 24-hour sleep/wake cycle are governed by a cluster of 10,000 brain cells called the suprachiasmatic nucleus. Sorting out what happens moment to moment is the focus of Eagleman’s work, and his Baylor-based Laboratory for Perception and Action is one of the only facilities dedicated to running experiments that produce hard data on how we perceive time.
Eagleman began his career researching vision, and in 2000 he became interested in the flash-lag effect, an optical illusion that scientists had never satisfactorily explained. On a computer screen, a blue doughnut-like ring circles a fixed point. Every so often, the ring’s hole turns white for a split second. Sometimes, the white center and the blue ring, which has continued on its path, appear to overlap. After running dozens of students through this test, Eagleman posited that it might be a temporal illusion, and that it tricks the brain, not the eyes. In addition to interpreting the white flash, the brain is also predicting where the blue ring should be a few milliseconds in the future, and that is being lumped in with the experience that reaches your consciousness. This was the first evidence that our perception of time is not an exact representation of what is occurring in the moment we consider to be the present.
A day before my jump, I visited Eagleman’s lab to try out some of his temporal illusions. Eagleman is 38 years old but looks younger by a decade. He has short brown hair, an athletic build and an affable manner. In 2009 his book Sum: Forty Tales from the Afterlives became a quick best seller. His lab looks like a traditional office, with cubicles and coffeepots and such, except the walls have been painted with a light blue dry-erase paint and are covered floor-to-ceiling with the markings of his research. But I’m staring instead at a computer screen, trying to click on a flitting green square.
In “9 Square,” nine blue squares are arranged like a tic-tac-toe board, and every now and again one of them turns green. My job is to click on the green square. At first, it jumps at a steady rate, moving to the next spot 200 milliseconds after I click the mouse. But after a while, the rate begins to vary and, when the green square moves faster, it seems to jump before I click on it.
“This is because your brain is constantly calibrating duration,” Eagleman explains. “If every time you flip on the lights there is a 200-millisecond delay, your brain recognizes the pattern and edits out the delay. Flip the switch, and the lights seem to turn on instantaneously. But if you moved to a funky house where the lights really did come on instantaneously, it would appear that they came on before you flipped the switch. Your brain is temporarily stuck on the old pattern.”
Eagleman had dozens of people play 9 Square while he scanned their brains with a functional-MRI machine. He found that when people experience the time delays, there is a boost of activity in the anterior cingulate cortex, which activates only when different parts of the brain process conflicting information. This suggested that the brain maintains at least two separate versions of time, a master clock that feeds you a perception of the now, and another that is constantly at work tidying up that perception.
Similar tests backed up his results, indicating that—unlike speech, which is processed in Broca’s area, or vision, which the occipital lobe handles—our sense of time is not centralized. Because of this, most scientists in the field have moved on to solving how parts of the brain work together to produce a single representation of time. But they first need to know if the system is truly capable of varying the rate at which it interprets the data. Eagleman remembered falling off a roof as a kid and how time seemed to stretch out forever in what was really only an instant. That’s when he decided that dropping people off a tower could be the way to figure all this out.single page
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