Rationally Speaking
A monthly e-column by Massimo
Pigliucci
Department of Botany,
University of Tennessee
N. 6, January 2001: "Split-brains, paradigm shifts, and why it
is so difficult to be a skeptic"
The human brain is a funny machine. Imperfectly designed
by natural selection, it finds itself in an environment that has little
resemblance with the one it evolved in. Gone is the savannah in which
our ancestors had to guard themselves from fierce creatures. Instead,
we live in a complex and ever expanding social milieu, our neighborhood
now encompassing the whole planet. Is it any wonder that our poor brains
are not doing so well in this brave new wired world?
Our brains seem to fail to grasp reality, as demonstrated
by the fact that a majority of Americans don't "believe" in
evolution (whatever "believing" in a scientific theory means),
while a sizable percentage is ready to accept the existence of an imaginary
all-powerful god, as well as of the devil, hell, and a sleuth of angels.
Why is it so difficult to be a reasonably skeptical person? What is
it that makes so many apparently intelligent people so gullible about
things that their brains clearly have the power to master? And-perhaps
most importantly for the skeptic-how do we get people to change their
minds in an informed way on so wide an array of irrationalities?
Obviously, I am not going to present the reader with
the magic bullet that can answer these questions, but a starting point
is being provided by recent research in neurobiology. It turns out that
lately we have learned a lot about how the brain works and why it makes
mistakes while interpreting reality. Since our most powerful tool doesn't
come with an owner's manual, it may pay off to spend a little time thinking
about how we think.
Perhaps one of the most dramatic ways we are learning
about the brain is by studying patients who literally have a split one.
The brain is made of two hemispheres, joined by a structure called the
corpus callosum which contains nerve fibers that continuously exchange
signals between the right and left hemisphere. Some individuals have
suffered more or less complete damage to the corpus callosum, either
because of a stroke or because of a surgical operation. These subjects
are invaluable to neurobiologists because it is possible to interrogate
the right and left hemispheres separately, see how differently they
think, and then piece this information together to reconstruct the thought
patterns of normal individuals. The problem with attempting to "talk"
to both hemispheres is that language is controlled by the left one,
the only hemisphere that can articulate things. Fortunately, the right
side can still "respond" to interrogations by virtue of its
control over the motor functions of the left half of the body, including
the arm and hand.
Perhaps the most astonishing thing neurobiologists
have discovered from split-brain patients is that the left hemisphere,
which normally "dominates" the right one, is literally in
charge of our view of the world. And it fights hard to preserve it.
In a wonderfully elegant experiment, a group of researchers led by Michael
Gazzaniga at Dartmouth College showed pictures to the right and left
hemispheres of a split-brain patient and then asked each hemisphere
to pick another picture to accompany the one originally presented. The
right side was shown (through the left half of the visual field) a house
with snow and, logically enough, it picked a shovel. The left hemisphere
was shown a chicken leg (through the right half of the visual field),
and it picked a chicken head-also quite logically. The experimenters
then verbally asked the patient to explain his choices. The left hemisphere
was the only one that could articulate an answer, but remember-it did
not know why his right counterpart had chosen a shovel, since the information
about the house with the snow did not cross the severed corpus callosum.
The patient's answer was as astounding as illuminating: "Oh, that's
simple. The chicken claw goes with the chicken [which was true], and
you need a shovel to clean out the chicken shed [which was coherent,
but completely false]." In other words, the left hemisphere acted
as an interpreter of the worldview of the individual and fabricated
a just-so story to fit all the available data!
These sort of experiments have shown that the left
hemisphere is in charge of our worldview, of the paradigms we currently
hold about a variety of aspects of reality. In normal patients, these
paradigms are constantly evaluated against external evidence, gathered
by both hemispheres through a suite of sensorial inputs. The left interpreter
has the all-important function of making sense of the world, and it
does a reasonably good job at it. However, when the incoming data is
insufficient, or when some piece of evidence contradicts the currently
held view, the left hemisphere either rejects the unfit information
or it distorts it so to make sense of it. This process of "rationalizing"
the world goes on up to a certain point. If the degree of conflicting
information is too high (i.e., there is too much dissonance between
what one believes and what one perceives) then that most stupendous
phenomenon suddenly occurs: we change our minds (literally)!
The problem that rational people face, then, is twofold.
On the one hand, the brain has evolved a powerful mechanism to avoid
to change its mind too often, which means that people will stubbornly
continue to believe all sorts of nonsense because it is less painful
than to radically alter their worldview. On the other hand, we know
that the problem is all the more insurmountable when the data fed to
the subject is poor, and unfortunately most of what modern human beings
are exposed to by the media is pure garbage.
However, there is no need to despair just yet. Understanding
the problem is a necessary (though by all means not sufficient) step
to solve it. Realizing where people's stubbornness (and sometimes our
own) comes from will help not getting unduly irritated or downright
nasty when facing patent irrationality in our fellow human beings. And
empathy is one important step toward connecting with anybody. The second
message of modern neurobiological research is perhaps an old one, but
which now comes with the weight of evidence: education is our (slow)
way out. What we need to do is to keep educating people, to feed good
information to the brain's interpreter. If neurobiologists are correct,
most brains will come to understand reality if properly nurtured. It
is ignorance which provides the necessity for just-so stories, with
all the tragic consequences that follow when people defend a flawed
worldview at all costs.
Next Month: "The greatest democracy in the world
and
the unfairness of American elections"
© by Massimo Pigliucci, 2001
