Page 68 - Miracle in the Eye

M MIRACLE IN THE EYE

You cannot see this spot because where the optic nerve enters the eye-
ball, there exists a small round area of the retina that has no cone or rod cells.
This optic disk, which is not sensitive to light, forms the blind spot of the eye.
With such a blind spot, how can we still see seamlessly? This is thanks
to the brain's supplementary ability. The missing part of your vision caused
by the blind spot is "painted" with whatever color most closely matches the
background, and thus camouflaged. 18
This is why you are unaware that you have a blind spot in the first
place!
In order to understand the concept better, refer to the test in Figure 2.5,
then follow these steps: Shut your right eye and hold this book 50 centimeters
(19.7 inches) away from your nose. Now, focusing only upon the red cross with
your left eye, slowly draw the book toward your nose. As the book comes
closer, you will see the red circle disappear, to be replaced by the background
pattern of diagonal lines. At this moment, you are blind to that spot. But you
perceive no gap in your vision, because your brain assumes that the spot would
contain the linear background. How the brain forms this assumption is a mys-
tery that neither psychologists nor neurologists have been able to solve. Some
have put forward a theory that each eye compensates for the blind spot of the
other eye, since with respect to the optic axis, the blind patch on one eye lies at
a different location than the other's. This is only part of the theory, however.
Defenders of this theory are far from an adequate explanation as to how we still
manage to see a continuous picture with only one eye. 19
We do know that the brain's "cover-up" for the blind spot is an illusion
we are made to believe and accept. This means that any vision that you think
is real may not be wholly accurate. It's a little like a dream: While it takes
place, you believe you are actively taking part in the events, while they are
nothing but an illusion created in your mind.
Now try another experiment. Look at the left-hand cross (in Figure 2.6)
with both eyes, for a full minute. Now, move your eyes to the right-hand
cross. In a few moments, color will appear around it, even if it isn't really
there. Your brain is fooling you—you are under the impression that some-
thing is there, when it's actually not.

66