Recognition

Vision is a bizarre combination of stimulus and interpretation. By itself, the torrent of lights and colors that makes up the sensory input of the second cranial nerve is merely noise, data picked up and mapped geographically onto receiving portions of your brain. This mapping, interpreted by your brain, allows you to interpret what you see. If section X lights up, your brain knows that whatever information you have received there come from the left side.

But you need more than just this somatotopy to interpret everything you see. You need associations, you need memory. Vision without memory is like listening to a foreign language. You hear the quality, tone, and speed of the sounds, but you don't understand the context. What is it to see an object if you don't know what it is? The significance assigned is what gives you interactivity with your world. This can be taken away from you. Neurological damage can remove your ability to tie visual stimuli to concepts, removing your understanding of the world around you.

For instance, damage to the fusiform gyrus can cause facial agnosia, destroying your ability to recognize the faces around you. You see everyones face, you can describe them, draw them. But you don't know them. The association, the connection between this pattern of intensity and color and your memory, is gone. Without it, a face just becomes a face, not someone's face. Imagine how isolating it must be, walking through hallways, down streets, never recognizing anyone. Imagine knowing your own face only through context, knowing yourself only because the face in the mirror must be you.

Icy Hot

In high school, a friend once took up a bet that he wouldn't slather icy hot over a most delicately indelicate region. He took the bet for money, a move made on the assumption that it wouldn't be that bad. Mere moments after slathering the viscous jelly on himself and he was clearly regretting his decision. His skin absorbed the active ingredients, menthol and methyl salicylate, and it was sending signals his brain interpreted as the damage of rapid freezing. His brain, convinced that he was somehow accidentally dipping his testicles in a vat of frozen water, was screaming at him that something was direly wrong.

The pain and temperature nervous system runs on different wiring than the rest. Temperature transmits more slowly to your brain, allowing a period of accommodation when changing one's climate. The nerves themselves lack the complicated mechanical apparatus of the somatic sensory, ending in uncomplicated open ports that merely change elements of biological function if the temperature becomes excessively high or low. The odd thing is that these sensors can also be triggered chemically.

The menthol and methyl salicylate of the icy hot had been absorbed by his skin, percolating into his system and encountering nerves dedicated to a purpose of discussing the weather. They bind to these nerves, triggering their activity, and sending a veritable tidal wave of information to the brain, all coded to mean the same thing: Cold. It is this mechanism that makes you feel the air cool when you take a cough drop (menthol), or burns the inside of your mouth when you eat a habanero pepper (capsaicin). For some reason we have an evolutionarily designed mechanism to interpret a chemical as hot or cold, to become sweaty when eating a burrito doused in hot sauce, or to feel a cool breeze merely by contacting menthol.

Perhaps it was a far sighted evolutionary attempt to teach my friend to exert better judgement.

Two Point Discrimination

We live in a bubble of interpretation, building a world around us piecemeal from the myriad of detective devices built into our frames. Information is recorded via physical or electrical media, interpreting pressure, chemicals, or light into coded patterns, messages which our brain instinctively interprets.

We feel the outside world via a series of pressure sensors. These sensors read vibrations and force, interpreting the combination into an understanding of texture and position. They combine with internal architecture, stretch receptors reporting the position of your joints. The brain synthesizes the feeling of pressure against your fingertips with the position of your muscles and bones, painting a picture by numbers of what it is you hold.

Your brain portrays the illusion of continuity, of a physical understanding of what you touch, and what is touching you. The distribution of nerves controls how precisely you can feel, allowing your fingers to read braille, while your legs can barely report more than contact. The phenomenon of sensory acuity is described by the phrase "two point discrimination." In the finger tips, you can feel two different points of contact at minute distances. In the back, the distance goes up to centimeters. I can hold two pens in my hand, touch them to your back at the same time, and your brain will report only one touch. The astonishing nature of this is not in your inability to discriminate, its in your brain's absolute conviction that there is only one pen. Even knowing full well that someone is holding two pens to your back, the only result is a cognitive dissonance between known and observed reality.

I marvel at this, the fact that your body and perception can so convincingly lie to you. It is very mystical in its implications, the idea that the physical, the body, cannot be trusted.