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.