vision and the detailed vision of the macula, the concentration of cones near
the center of the retina. The neural impulses from these two sets of rods and
cones are transmitted to the brain, where they are integrated and interpreted
to assemble an understanding of the objects around us. When you think this
process through, this is the part that is truly amazing. The brain keeps track of
position, motion, and orientation, and integrates the signals from two separate
receptors to perceive
depth. With the merest glance and without conscious
thought, you know that the variation in reflected light is a pencil on the table,
and that it is about two feet away from you. Again without conscious thought,
you could reach over and pick it up—without even looking at it directly. It’s
really pretty amazing.
The brain uses a huge variety of very subtle details and cues to interpret and
understand what the eyes are registering. And because of this, the brain is quite
forgiving. It can utilize existing knowledge to fill in blanks that are poorly
perceived; through depth perception and slight motion, the brain can piece
together what an object is even when it is just on the edge of visibility. Slight
motions of the head and eyes apparently play a huge role in supplying the
brain with enough data to accurately interpret the world “out there,” outside
of ourselves.
This is actually quite important for our topic of study because when we
translate that complex, 3D world of trees and rocks and dust bunnies under
beds into a two-dimensional representation, the brain
suddenly loses several of the subtle cues that it
uses to interpret the world. In particular, we
find that it does not fill in blanks or vague
areas in the same way. So whether the twodimensional
representation is a television
screen or a photographic print or a line drawing,
the creator of the representation must compensate for
what is missing. In short, the representation needs to be better drawn and
more carefully created than the reality would have to be. The important elements
must be clear and well defined. Sometimes it is effective even to blur
out nonessential elements to help focus the eye (and the mind) on what is
essential.
Let me give an example of what I’m talking about here. Suppose you’re sitting
in a dimly lit room you are unfamiliar with. Something in the corner
catches your eye; you can’t quite tell what it is. So you’ll move your head a
little bit, giving the brain extra data about the dimly perceived object; you
may squint or shield your eyes from the light source to allow you a little better
dim light perception. The little bit of extra information gained from this
movement may allow you to figure out what the object is. If it’s not enough,
you always have the option of getting up and walking over there, or of turning
on another light. And if that fails, you can still
