FoundationalConceptsNeuroscience

ality. What is it that exists?
Next, our experience of the world depends on the physical proper-
ties of our sensory receptors: eyes are sensitive to a limited range of
energies of electromagnetic radiation, ears to a limited range of fre-
quencies of mechanical vibration, noses to a limited range of molec-
ular shapes, and so forth. Then, signals from sensory receptors are
manipulated by the nervous system and, particularly in us humans,
by our brain. Billions of cells and trillions of synaptic connections
are impacted by information received via sensory pathways. This
interaction of neural networks with incoming sensory information
somehow forms the basis, it is believed, for our mental experience
of the world. In philosophy, this is the realm of epistemology: how do
we know what we know? In summary, according to the conventional
framework in the neuroscience of perception, our experience of the
world is a function of what actually exists, the physics of our sensory
receptors and organs, and the neural manipulation of incoming sig-
nals by the brain.
There is a notion in epistemology called naive realism, that what we
perceive is identical to what actually exists in the world—what we see,
hear, smell, taste, and so forth, is exactly what is “out there” in some
way. It is very easy to demonstrate the limitations of naive realism.
Figure 11.3 is called the café wall illusion, inspired by a tile pattern
on the wall of a coffee house in Bristol, England. Most people see lines
that are not parallel, that are askew. However, you can easily verify by
using a straightedge that all lines are indeed parallel. This simple but
powerful visual illusion clearly illustrates that what we perceive (in
this case, see) is not exactly what is.