The New Yorker, April 2011
Edited by Andy Ross
David Eagleman, 39, is an assistant professor of neuroscience at Baylor
College of Medicine, in Houston. He has spent the past decade tracing the
neural and psychological circuitry of the brain's biological clocks.
Brain time, as Eagleman calls it, is intrinsically subjective. How much of
what we perceive exists outside of us and how much is a product of our
minds? Time is a dimension like any other, yet the data rarely matches our
reality. The jittery camera shake of everyday vision is smoothed over and
our memories are often radically revised.
A few years ago, Eagleman
ran an experiment to investigate the slowing down of perceived time under
stress. First, Eagleman and a graduate student developed a perceptual
chronometer. The unit could be strapped to a subject's wrist, where it would
flash a number at a rate just beyond the threshold of perception. If time
slowed down, Eagleman reasoned, the number would become visible. Then his
team built SCAD, a "suspended catch air device." At the top of a tower, a
subject would be hooked to a cable and lowered through a hole in the floor.
His back would be to the ground, his eyes looking straight up. When the
cable was released, he would plummet 110 feet, in free fall, until a net
caught him near the ground.
A sense of time is threaded through
everything we perceive. In Eagleman's 2009 essay "Brain Time," he writes
that the brain is like Kublai Khan, enthroned in its skull, "encased in
darkness and silence," at a lofty remove from brute reality. Messengers
stream in from every corner of the sensory kingdom, bringing word of distant
sights, sounds, and smells. Their reports arrive at different rates, often
long out of date, yet the details are all stitched together into a seamless
chronology. Kublai Khan was piecing together the past. The brain is
describing the present.
Eagleman's mother was a biology teacher, his
father a psychiatrist. As an undergraduate at Rice, Eagleman wanted to be a
writer, but his parents persuaded him to major in electrical engineering.
An extended sabbatical ensued. After his sophomore year, Eagleman joined the
Israeli Army as a volunteer, then spent a semester at Oxford studying
political science and literature, and finally moved to Los Angeles to become
a screenwriter and a standup comic.
Back at Rice, he began to read
books about the brain in his spare time and decided to take a course in
neurolinguistics. For his doctoral work at Baylor, he programmed a piece of
virtual neural tissue so complex that it tied up the Texas Medical Center’s
new supercomputer for days. Eagleman's program showed that brain cells can
exchange information not just through neurotransmitters but through the ebb
and flow of calcium atoms. He went on to earn a postdoc at the Salk
Institute, near San Diego. There he fell under the spell of Francis Crick.
Like Crick, Eagleman was fascinated by consciousness. He thought of time
as a window on the movements of the mind. In a 2000 paper, Eagleman looked
at the flash-lag effect. His version of the illusion consisted of a white
dot flashing on a screen as a green circle passed over it. To determine
where the dot hit the circle, Eagleman found, his subjects' minds had to
travel back and forth in time. They saw the dot flash, then watched the
circle move and calculated its trajectory, then went back and placed the dot
on the circle. It was not prediction but postdiction.
reach the brain within 100 ms of one another, any
differences in processing are erased. The margin of error is surprisingly
wide. Decades ago, Benjamin Libet, at the University of California, San
Francisco, tested this by stimulating the cortical neurons of patients with
electrical pulses. The subjects felt a tingle in the body parts wired to the
neurons, but the stimulus didn't register for up to half a second.
Eagleman says that, like
Kublai Khan,the brain needs time to get its story straight. It
gathers up all the evidence of our senses, and only then reveals it to us.
Perception and reality are often a little out of register. If all our senses
are slightly delayed, we have no context by which to measure a given lag.
Reality is carefully censored before it reaches us.
Eagleman ran the
first round of SCAD experiments in 2007, with twenty subjects. He programmed
the perceptual chronometer to flash its numbers just a little too fast to be
legible. Then he stationed one observer at the top of the tower, to make
sure the riders looked at the chronometer as they fell, and another on the
ground. Afterward, the riders would report their chronometer readings, then
take a stopwatch and go back over the experience in their minds, timing it
from start to finish. Eagleman knew how long the fall took in real time and
wanted to know how long it felt. On average, the subjects overestimate the
length of their fall by 36 percent. But no matter how hard they stare at the
chronometer, they can't read the numbers.
When something threatens
your life, the amygdala seems to kick into overdrive, recording every last
detail of the experience. The more detailed the memory, the longer the
moment seems to last. "Time is this rubbery thing," Eagleman said. "It
stretches out when you really turn your brain resources on, and when you
say, 'Oh, I got this, everything is as expected,' it shrinks up."
Early this winter, Eagleman was in London for a study of time perception in
drummers. The idea of studying drummers had come from Brian Eno, the
composer, record producer, and former member of the band Roxy Music. Eno
first met Eagleman two years ago, after a publisher he knew sent him a book
of Eagleman's short stories, called Sum.
Sum has forty chapters,
each describing a different version of the afterlife. Eagleman establishes a
set of initial conditions, then lets the implications unfold logically.
took years to find a publisher. In England, reviewer Geoff Dyer called it
"stunningly original" and saw in it "the unaccountable, jaw-dropping quality
of genius." Scientists and religious readers alike praised it.
suggested a staged reading of the book. The production premièred at the
Sydney Opera House in June 2009, with a score by Eno. There Eno told
Eagleman the story that inspired the drumming study. Eagleman arrived at
Eno's studio the next day carrying a pair of laptops and a wireless EEG
monitor. He clamped the EEG on his head and watched as sixteen wavering
lines represented the electrical activity at points in his brain. The drummers would wear this while taking a
set of four tests.
Eno was right: drummers have more exact time
perception than most people. Eagleman planned to use the EEG data to locate
the most active areas of the drummers' brains, then target them with bursts
of magnetic stimulation to see if he could disrupt their timing.
May, Pantheon publishes Eagleman's popular account of the unconscious,
AR I guess this is a man to take seriously.
Like him, I think our perception of time is crucial to understanding how the
brain supports our consciousness.