The Mystery of Our Sensory World
ERAN MUKAMEL
SHMA.COM
For most of us, our sensory intercourse with the world feels effortless, even au- tomatic. The colors and shapes of objects around us fill our vision the moment we
open our eyes; hearing requires even less initiative. Odors, both pleasant and noxious, intrude on our experience without any
conscious act of our will. We easily take our
sensory perception for granted and yet we
place hearing — or, perhaps, listening — at the
head of Jewish tradition’s most recognizable
prayer: Sh’ma. Why does the commonplace
act of listening provide the basis for renewing
and affirming a spiritual connection?
One of the brain’s functions is the construction
of a coherent system of meanings for the
objects of our sensory experience.
Eran Mukamel is a Swartz
Postdoctoral Fellow in
theoretical neuroscience at
Harvard's Center for Brain
Science. His interests range
from the mechanisms our
brains use to perceive, decide,
remember, and act, to the
application of mathematical
and statistical methods to
neural network models. He
can be reached at
eran@post.harvard.edu.
To a neuroscientist, sensory perception is
more complex and more mysterious than our
conscious experience suggests. After the eyelids are opened, a marvelously intricate and
elegant chain of molecular and cellular events
conveys and processes visual information to
produce the interrelated phenomena of perception. We perceive seemingly stable, coherent images and sounds without being aware
of the ways these images are reconstructed by
our sense organs. Some of the links in the
chain of perception are more or less understood, such as the formation of an image by
the lens on the back of the eye (the retina) and
the absorption of photons by the pigment in
photoreceptor cells. But after these early
stages that convert light into graded electrical
responses, increasingly elaborate networks of
nerve cells take over the processing and transmission of the visual world.
Neural networks have evolved to let us interact with a varied and constantly changing
environment. Where is my food, my friend,
my mate? How big is that pothole, and how
friendly is that dog? Our need for knowledge
of the environment is constant and visceral.
Yet the raw material provided by our sense organs can be quite inadequate. High-resolution
visual information is available from only a
small region at the center of each eye’s field of
view. To compensate, our gaze shifts constantly, several times every second, to bring
new details and features of the visual scene
into the focus of this high-acuity region. To
gather data about our surroundings we reach
out to the world with our eyes as much as we
do with our hands.
The ears, with their immobile flaps of skin
and ever-receptive pores, belie the fundamentally active way in which we perceive the
auditory world around us. To make sense of
the world, the brain filters, selects, and am-plifies those few key elements comprising the
current objects of our interest. Without this
ability, we could not distinguish the words of
an interlocutor who will presently expect an
intelligent and appropriate response from the
background of similar sounds coming from all
directions. Our auditory behavior is remarkably adapted to serve our behavioral needs.
In fact, it seems the processing of sound in
even the earliest stages of our auditory cortex
can be modulated in significant ways by context and higher cognitive processes. We may
not hear only what we’re listening for, but
what we hear is certainly a product of active
auditory behavior.
The brain has evolved to cope with a dangerous, competitive, and uncertain world by
taking in sensory information and constructing stable and useful representations. In a
sense, the brain deals constantly with puzzles,
challenges, and mysteries posed by the arrival
of incomplete and noisy information from the
senses. It may be that our search for spiritual
comfort in the face of the unknown is not simply analogous or poetically akin to groping in
the dark. In fact, the neural computations we
use to reach out and comprehend our sensory
world may be paradigmatic of the other more
private but no less necessary and salient, computations our brains use to perform their other
cognitive functions. One of these functions is
surely the construction of a coherent system
of meanings for the objects of our sensory experience. The injunction sh’ma reminds us
that we bring the world into our own experience when we listen, and we relate to the
great mysteries of our universe through an ongoing process of actively reaching out.
