Brain Rules (Updated and Expanded)

Eye Meets Wireframe
. It is composed only of outlines, or edges.
Another makes a film you might call 
Eye Meets Motion
, processing only the
movement of an object (and often in a specific direction). Another makes
Eye Meets Shadows
. There may be as many as 12 of these tracks operating
simultaneously in the retina, sending off interpretations of specific features
of the visual field. This new view is quite unexpected. It’s like discovering
that the reason your TV gives you feature films is that your cable is infested
by a dozen independent filmmakers, hard at work creating the feature while
you watch it.

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Rivers of visual information
These movies now stream out from the optic nerve, one from each eye,
and flood the thalamus, that egg-shaped structure in the middle of our heads
that serves as a central distribution center for most of our senses. If these
streams of visual information can be likened to a large, flowing river, the
thalamus can be likened to the beginning of a delta. Once the information
leaves the thalamus, it travels along increasingly divided neural streams.
Eventually, thousands of small neural tributaries will be carrying parts of
the original information to the back of the brain. (Put your hand on the back
of your head. Your palm is now less than a quarter of an inch away from the
visual cortex, the area of the brain that is currently allowing you to see these
words.) The information drains into a large complex region within the
occipital lobe called the visual cortex.
Once they reach the visual cortex, the various streams flow into specific
parcels. There are thousands of lots, and their functions are almost
ridiculously specific. Some parcels respond only to diagonal lines, and only
to specific diagonal lines (one region responds to a line tilted at 40 degrees,
but not to one tilted at 45 degrees). Some process only the color information
in a visual signal; others, only edges; others, only motion.
This means you can damage the region of the brain in charge of, say,
motion, and get an extraordinary deficit. You’d be able to see and identify
objects quite clearly, but not tell whether the objects are stationary or
moving. This happened to a patient known to scientists as L.M. It’s called
cerebral akinetopsia, or motion blindness. L.M. perceives a moving object
as a progressive series of still snapshots—like looking at an animator’s
drawings one page at a time. This can be quite hazardous. When L.M.
crosses the street, for example, she can see a car, but she does not know if it
is actually coming at her.
L.M.’s experience illustrates just how modular visual processing is. And
if that was the end of the visual story, we might perceive our world with the
unorganized fury of a Picasso painting—a nightmare of fragmented objects,
untethered colors, and strange, unboundaried edges. But that’s not what
happens, because of what takes place next. The brain reassembles the
scattered information. Individual tributaries start recombining, merging,
pooling their information, comparing their findings, and then sending their

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analysis to higher brain centers. The centers gather these hopelessly
intricate calculations from many sources and integrate them at an even more
sophisticated level. Higher and higher they go, eventually collapsing into
two giant streams of processed information. One of these, called the ventral
stream, recognizes what an object is and what color it possesses. The other,
termed the dorsal stream, recognizes the location of the object in the visual
field and whether it is moving.
“Association cortices” do the work of integrating the signals. They
associate—or, better to say, reassociate—the balkanized electrical signals.
Then you see something. So the process of vision is not as simple as a
camera taking a picture. The process is more complex and more convoluted
than anyone could have imagined. There is no real scientific agreement
about why this disassembly and reassembly strategy occurs.
Complex as visual processing is, things are about to get worse.
You’re hallucinating right now
You might inquire whether I had too much to drink if I told you right now
that you were actively hallucinating. But it’s true. At this very moment,
while reading this text, you are perceiving parts of this page that do not
exist. Which means you, my friend, are hallucinating. I am about to show
you that your brain actually likes to make things up, that it is not 100
percent faithful to what the eyes broadcast to it.