14 ASTRONOMY • FEBRUARY 2018S
eeing is believing. Or
is it? In his inf luen-
tial 1950 book The
Perception of the
Visual World, psy-
chologist James J. Gibson argued
that our conscious perceptions
come to us directly through our
senses. This outside-in notion
of perception might seem like
common sense, but common
sense can be wrong. And as it
happens, this common sense
description of conscious percep-
tion is about as wrong as it gets!
As cognitive scientists dig
deeper into the workings of the
brain, they have discovered that
the world of our perceptions
— the only world we ever con-
sciously experience — isn’t a
direct representation of external
reality at all. Instead, it is a car-
toon world of sorts, constructed
from the inside out. According
to Anil Seth, co-director of the
Sackler Centre for Consciousness
Science, “Your brain hallucinates
your conscious reality.”Prediction machine
Seth refers to the brain as a
“prediction machine” that main-
tains its own internal model
of what is going on beyond the
borders of consciousness. It uses
that theory of the world to make
predictions about future infor-
mation from the senses, then
compares those predictions with
sensory data as it arrives. When
the two agree, all is well. But
when sensory data don’t match
the brain’s predictions, the neu-
ral circuits that build our con-
sciousness shift into high gear
resolving the differences.FORYOURCONSIDERATION
BY JEFF HESTERConstrained
hallucinations
How the brain uses science to perceive the world.When predictions and data
disagree, your brain does the
obvious thing: It makes a best
guess. Cognitive scientists speak
of the Bayesian brain in refer-
ence to Bayes’ theorem for infer-
ring probabilities from a
combination of data and prior
knowledge. Ultimately your
brain modifies its model of the
world until predictions again
agree with sensory data.
This process takes time; per-
ceptions lag a few hundred mil-
liseconds behind actual events.
The things you consciously
experience happened awhile
ago, but you don’t perceive them
until your brain incorporates
them into its internal model.
Hmmm ... starting with a
theory ... making testable pre-
dictions ... comparing those
predictions with data ... recon-
ciling theory with data when
they are at odds ...
All of that sounds kind of
familiar. Or at least it should
sound familiar if you’ve read
many of my columns or remem-
ber the scientific method from
high school. Perception is a
product of hypothesis testing.
The process we use to perceive
the world is for all intents and
purposes a restatement of Karl
Popper’s description of how
falsifiable predictions are used
to test scientific knowledge.
In short, we perceive the
world via a biologically evolved
implementation of Popper’s
epistemology of science. Pardon
me for using the vernacular of
my youth, but far out!
The parallels between con-
scious perception and scientificknowledge don’t stop there.
Scientific theories don’t just
appear out of the blue. Theories
get their start when people
observe phenomena in the
world, then scratch their heads
about just what might be going
on. Similarly, a brain’s percep-
tual model doesn’t spring fully
formed from nowhere. The men-
tal model used to generate your
conscious experience is built up
through a lifetime of learning,
exploration and discovery.In a child’s eye
If you are a parent, you have
seen this remarkable process at
work. A newborn baby is awash
in sensory information. Light
sensitive cells in her eyes fire.
Her ears turn sound waves into
neurological signals. But watch
her look around. She detects
motion, which generates the
most basic type of difference sig-
nal there is. She also sees faces
and recognizes voices. Those
are so important to humans that
evolution hard-wired them into
the brain’s neural networks.
But your newborn daughter
doesn’t perceive chairs, or
tables, or meaning in words.
How can she? Lacking an
understanding of spatial rela-
tionships, objects and their
properties or the meaning of
language, she has nothing to
project into her perceptions!
Her brain is ready to discover
the world, but for now she doesnot even perceive a difference
between herself and the rest of
the world; only later will she
develop consciousness of self.
Not all internal models of the
world are equally valid, but they
are unique. Since each of us has
our own set of genes, knowl-
edge, and experiences, we also
have our own mental model of
the world. That means that each
of us consciously experiences
the world differently. When a
physicist and a lawyer look at
the world, they don’t just under-
stand things differently; they
consciously perceive things dif-
ferently! A hundred people
might occupy the same physical
room, but consciously they
inhabit a hundred different
rooms that might bear little
resemblance to each other.
There is a thought for you.
We all share the same objective
reality. But the nature of the
world you consciously experi-
ence, constructed by your
brain using the same approach
to knowledge that powers sci-
ence, is yours and yours alone.
Who knows? Maybe reading
this column will modify your
internal model enough to
change your conscious percep-
tion of your conscious percep-
tions themselves!BROWSE THE “FOR YOUR CONSIDERATION” ARCHIVE AT http://www.Astronomy.com/Hester.Jeff Hester is a keynote speaker,
coach, and astrophysicist.
Follow his thoughts at
jeff-hester.com.© ARTISTICCO LLC | DREAMSTIME