A Famous Argument Against Free Will Has Been Debunked
[[Very technical article, but for those who know of
the research it is an excellent example of how a definite proof against free
will can be based on a pure mistake.]]
For decades, a landmark brain study fed
speculation about whether we control our own actions. It seems to have made a
classic mistake.
Sep 10, 2019
https://www.theatlantic.com/health/archive/2019/09/free-will-bereitschaftspotential/597736/
[[And here is the original article
https://mail.google.com/mail/u/0/#inbox/FMfcgxwDrHsnkjfWCWKVRSGDcqnmVpdM?projector=1&messagePartId=0.1]]
[[And here is the original article
https://mail.google.com/mail/u/0/#inbox/FMfcgxwDrHsnkjfWCWKVRSGDcqnmVpdM?projector=1&messagePartId=0.1]]
The death of free will began with thousands of finger taps. In
1964, two German scientists monitored the electrical activity of a dozen
people’s brains. Each day for several months, volunteers came into the
scientists’ lab at the University of Freiburg to get wires fixed to their scalp
from a showerhead-like contraption overhead. The participants sat in a chair,
tucked neatly in a metal tollbooth, with only one task: to flex a finger on
their right hand at whatever irregular intervals pleased them, over and over,
up to 500 times a visit.
The purpose of this experiment was to search for signals in the
participants’ brains that preceded each finger tap. At the time, researchers
knew how to measure brain activity that occurred in response to events out in
the world—when a person hears a song, for instance, or looks at a
photograph—but no one had figured out how to isolate the signs of someone’s
brain actually initiating an action.
The experiment’s results came in squiggly, dotted lines, a
representation of changing brain waves. In the milliseconds leading up to the
finger taps, the lines showed an almost undetectably faint uptick: a wave that
rose for about a second, like a drumroll of firing neurons, then ended in an
abrupt crash. This flurry of neuronal activity, which the scientists called
the Bereitschaftspotential, or readiness potential, was like a gift
of infinitesimal time travel. For the first time, they could see the brain
readying itself to create a voluntary movement.
This momentous discovery was the beginning of a lot of trouble
in neuroscience. Twenty years later, the American physiologist Benjamin Libet
used the Bereitschaftspotential to make the case not only that the brain
shows signs of a decision before a person acts, but that, incredibly, the
brain’s wheels start turning before the person even consciously intends to do
something. Suddenly, people’s choices—even a basic finger tap—appeared to be
determined by something outside of their own perceived volition.
As a philosophical question, whether humans have control over
their own actions had been fought over for centuries before Libet walked into a
lab. But Libet introduced a genuine neurological argument against free will.
His finding set off a new surge of debate in science and philosophy circles.
And over time, the implications have been spun into cultural lore.
Today, the notion that our brains make choices before we are
even aware of them will now pop up in cocktail-party conversation or in a
review of Black Mirror.
It’s covered by mainstream journalism outlets, including This American Life, Radiolab, and this magazine. Libet’s
work is frequently brought up by popular intellectuals such as Sam Harris and
Yuval Noah Harari to argue that science has proved humans are not the authors
of their actions.
It would be quite an achievement for a brain signal 100 times
smaller than major brain waves to solve the problem of free will. But the story
of the Bereitschaftspotential has one more twist: It might be
something else entirely.
The Bereitschaftspotential was never meant to
get entangled in free-will debates. If anything, it was pursued to show that
the brain has a will of sorts. The two German scientists who discovered it, a
young neurologist named Hans Helmut Kornhuber and his doctoral student Lüder
Deecke, had grown frustrated with their era’s scientific approach to the brain
as a passive machine that merely produces thoughts and actions in response to
the outside world. Over lunch in 1964, the pair decided that they would figure
out how the brain works to spontaneously generate an action. “Kornhuber and I
believed in free will,” says Deecke, who is now 81 and lives in Vienna.
To pull off their experiment, the duo had to come up with tricks
to circumvent limited technology. They had a state-of-the-art computer to
measure their participants’ brain waves, but it worked only after it detected a
finger tap. So to collect data on what happened in the brain beforehand, the
two researchers realized that they could record their participants’ brain
activity separately on tape, then play the reels backwards into the computer.
This inventive technique, dubbed “reverse-averaging,” revealed the Bereitschaftspotential.
The discovery garnered widespread attention. The Nobel laureate
John Eccles and the prominent philosopher of science Karl Popper compared the
study’s ingenuity to Galileo’s use of sliding balls for uncovering the laws of
motion of the universe. With a handful of electrodes and a tape recorder,
Kornhuber and Deecke had begun to do the same for the brain.
What the Bereitschaftspotential actually meant,
however, was anyone’s guess. Its rising pattern appeared to reflect the
dominoes of neural activity falling one by one on a track toward a person doing
something. Scientists explained the Bereitschaftspotential as
the electrophysiological sign of planning and initiating an action. Baked into
that idea was the implicit assumption that the Bereitschaftspotential causes
that action. The assumption was so natural, in fact, no one second-guessed
it—or tested it.
Libet, a researcher at the University of California at San
Francisco, questioned the Bereitschaftspotential in a
different way. Why does it take half a second or so between deciding to tap a
finger and actually doing it? He repeated Kornhuber and Deecke’s experiment,
but asked his participants to watch a clocklike apparatus so that they could
remember the moment they made a decision. The results showed that while
the Bereitschaftspotential started to rise about 500
milliseconds before the participants performed an action, they reported their
decision to take that action only about 150 milliseconds beforehand. “The brain
evidently ‘decides’ to initiate the act” before a person is even aware that
decision has taken place, Libet concluded.
To many scientists, it seemed implausible that our conscious
awareness of a decision is only an illusory afterthought. Researchers
questioned Libet’s experimental design, including the precision of the tools
used to measure brain waves and the accuracy with which people could actually
recall their decision time. But flaws were hard to pin down. And Libet, who
died in 2007, had as many defenders as critics. In the decades since his experiment,
study after study has replicated his finding using more modern technology such
as fMRI.
But one aspect of Libet’s results sneaked by largely
unchallenged: the possibility that what he was seeing was accurate, but that
his conclusions were based on an unsound premise. What if the Bereitschaftspotential didn’t
cause actions in the first place? A few notable studies did suggest this, but
they failed to provide any clue to what the Bereitschaftspotential could
be instead. To dismantle such a powerful idea, someone had to offer a real
alternative.
In 2010, Aaron Schurger had an epiphany. As a researcher at the
National Institute of Health and Medical Research in Paris, Schurger studied
fluctuations in neuronal activity, the churning hum in the brain that emerges
from the spontaneous flickering of hundreds of thousands of interconnected
neurons. This ongoing electrophysiological noise rises and falls in slow tides,
like the surface of the ocean—or, for that matter, like anything that results
from many moving parts. “Just about every natural phenomenon that I can think
of behaves this way. For example, the stock market’s financial time series or
the weather,” Schurger says.
From a bird’s-eye view, all these cases of noisy data look like
any other noise, devoid of pattern. But it occurred to Schurger that if someone
lined them up by their peaks (thunderstorms, market records) and
reverse-averaged them in the manner of Kornhuber and Deecke’s innovative
approach, the results’ visual representations would look like climbing trends
(intensifying weather, rising stocks). There would be no purpose behind
these apparent trends—no prior plan to cause a storm or bolster the market.
Really, the pattern would simply reflect how various factors had happened to
coincide.
“I thought, Wait a minute,” Schurger says. If he
applied the same method to the spontaneous brain noise he studied, what shape
would he get? “I looked at my screen, and I saw something that looked
like the Bereitschaftspotential.” Perhaps, Schurger realized,
the Bereitschaftspotential’s rising pattern wasn’t a mark of a
brain’s brewing intention at all, but something much more circumstantial.
Two years later, Schurger and his colleagues Jacobo Sitt and
Stanislas Dehaene proposed an
explanation. Neuroscientists know that for people to make any type of decision,
our neurons need to gather evidence for each option. The decision is reached
when one group of neurons accumulates evidence past a certain threshold.
Sometimes, this evidence comes from sensory information from the outside world:
If you’re watching snow fall, your brain will weigh the number of falling
snowflakes against the few caught in the wind, and quickly settle on the fact
that the snow is moving downward.
But Libet’s experiment, Schurger pointed out, provided its
subjects with no such external cues. To decide when to tap their fingers, the
participants simply acted whenever the moment struck them. Those spontaneous
moments, Schurger reasoned, must have coincided with the haphazard ebb and flow
of the participants’ brain activity. They would have been more likely to tap
their fingers when their motor system happened to be closer to a threshold for
movement initiation.
This would not imply, as Libet had thought, that people’s brains
“decide” to move their fingers before they know it. Hardly. Rather, it would
mean that the noisy activity in people’s brains sometimes happens to tip the
scale if there’s nothing else to base a choice on, saving us from endless
indecision when faced with an arbitrary task. The Bereitschaftspotential would
be the rising part of the brain fluctuations that tend to coincide with the
decisions. This is a highly specific situation, not a general case for all, or
even many, choices.
Other recent studies support the idea of the Bereitschaftspotential as
a symmetry-breaking signal. In a study of monkeys tasked with choosing
between two equal options, a separate team of researchers saw that a monkey’s
upcoming choice correlated with its intrinsic brain activity before the monkey
was even presented with options.
In a new study under review for publication in the Proceedings
of the National Academy of Sciences, Schurger and two Princeton researchers
repeated a version of Libet’s experiment. To avoid unintentionally
cherry-picking brain noise, they included a control condition in which people
didn’t move at all. An artificial-intelligence classifier allowed them to find
at what point brain activity in the two conditions diverged. If Libet was
right, that should have happened at 500 milliseconds before the movement. But
the algorithm couldn’t tell any difference until about only 150 milliseconds
before the movement, the time people reported making decisions in Libet’s
original experiment.
In other words, people’s subjective experience of a
decision—what Libet’s study seemed to suggest was just an illusion—appeared to
match the actual moment their brains showed them making a decision.
When Schurger first proposed the neural-noise explanation,
in 2012, the paper didn’t
get much outside attention, but it did create a buzz in neuroscience.
Schurger received awards for
overturning a long-standing idea. “It showed the Bereitschaftspotential may
not be what we thought it was. That maybe it’s in some sense artifactual, related
to how we analyze our data,” says Uri Maoz, a computational neuroscientist at
Chapman University.
For a paradigm shift, the work met minimal resistance. Schurger
appeared to have unearthed a classic scientific mistake, so subtle that no one
had noticed it and no amount of replication studies could have solved it,
unless they started testing for causality. Now, researchers who questioned
Libet and those who supported him are both shifting away from basing their
experiments on the Bereitschaftspotential. (The few people I found
still holding the traditional view confessed that they had not read Schurger’s
2012 paper.)
“It’s opened my mind,” says Patrick Haggard, a neuroscientist at
University College London who collaborated with Libet and reproduced the original
experiments.
It’s still possible that Schurger is wrong. Researchers broadly
accept that he has deflated Libet’s model of Bereitschaftspotential,
but the inferential nature of brain modeling leaves the door cracked for an
entirely different explanation in the future. And unfortunately for
popular-science conversation, Schurger’s groundbreaking work does not solve the
pesky question of free will any more than Libet’s did. If anything, Schurger
has only deepened the question.
Is everything we do determined by the cause-and-effect chain of
genes, environment, and the cells that make up our brain, or can we freely form
intentions that influence our actions in the world? The topic is immensely
complicated, and Schurger’s valiant debunking underscores the need for more
precise and better-informed questions.
“Philosophers have been debating free will for millennia, and
they have been making progress. But neuroscientists barged in like an elephant
into a china shop and claimed to have solved it in one fell swoop,” Maoz says.
In an attempt to get everyone on the same page, he is heading the first intensive research
collaboration between neuroscientists and philosophers, backed
by $7 million from two private foundations, the John Templeton Foundation and
the Fetzer Institute. At an inaugural conference in March, attendees discussed
plans for designing philosophically informed experiments, and unanimously
agreed on the need to pin down the various meanings of “free will.”
In that, they join Libet himself. While he remained firm on his
interpretation of his study, he thought his experiment was not enough to
prove total determinism—the idea that all events are set in
place by previous ones, including our own mental functions. “Given the issue is
so fundamentally important to our view of who we are, a claim that our free
will is illusory should be based on fairly direct evidence,” he wrote in a 2004
book. “Such evidence is not available.”
We want to hear what you think
about this article. Submit a letter to
the editor or write to letters@theatlantic.com.
Bahar Gholipour is a New York–based tech
and science journalist who covers the brain, neuroscience and psychology,
genetics and AI.