Page 138 - Darwin's Dilemma: The Soul

Darwin’s Dilemma: The Soul

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P Perceptual Defects in the Brain and a
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D Different External World
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When our five senses—which convince us that what we see is
the real world—are deprived of the electrical signals that give rise
to perceptions, the external world disappears. It is a scientific fact
that the senses provide information only by way of electrical sig-
nals. If there is plentiful information in the outside world, but the
relevant electrical signals fail to register, we will be unaware of it.
Errors of perception in the brain are some of the most impor-
tant proofs of this. For example, if you look at a room in full day-
light and imagine you are seeing it completely, the reality is differ-
ent. There is one very small point of the room in front of you that
you cannot see. And that missing spot remains wherever you look.
This is the “blind spot,” present in every human being in the cen-
ter of the retina where the optic nerve departs for the brain.
The cause of this blindness is the fact that the cells of the reti-
na are absent in just that one spot in the retina. Nonetheless, you
see the image before you utterly flawlessly. The reason is the com-
pensatory nature of the brain. The area that cannot be seen because
of the blind spot becomes “visible” because of the brain’s ability to
“color in” and “complete” the other details in the background. This
is an extraordinary state of affairs. There literally exists no infor-
mation in that blind spot, and whatever details the brain creates
there is entirely illusory. Yet we never know that we “cannot see”
that spot. The brain “papers over” the blind spot by making its
own best estimate of what ought to be there. But how is that esti-
mate made? That question still represents a puzzle for scientists.
Vilayanur S. Ramachandran describes this secret:
For example, you could try “aiming” your blind spot at the corner
of a square. Noticing the other three corners, does your visual sys-
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