Precisely how our vision works is more surprising than you might think. It's not exactly just a camera pointed out at the world. The brain has all sorts of processing shortcuts that help us get the visual information we need without overtaxing our mental resources.

In a wonderful and wide-ranging interview, Oliver Sacks explores precisely that topic with science writer Steve Silberman on the latter's new blog, NeuroTribes. Silberman, a long-time writer for Wired and other magazines, has produced wonderful example of what you might call slow-form blogging. It feels like a blog, that is to say, approachable and personal, but it also has the polish of a mag feature.

Sacks has turned his battle with cancer of the eye into a stunning series of experiments. His keen observation powers have turned inward. Here, Sacks talks about how his brain is able to fill in things that he knows his eyes can't see.

In general terms, I learned that the brain is always busy. In particular, if a sensory input -- whether it be vision or hearing or kinesthesia -- is taken away, there will be some sort of compensation, and the cortical systems involved in those representations will become hyperactive. This first became clear to me when I spoke to various blind people. One man, for example, who had lost his sight when he was about 20, said that when he read Braille, he didn't feel it in his fingers, he saw it. And there's nice evidence that the occipital areas of the brain, and the inferotemporal areas -- visual areas -- are excited in that sort of situation.

For myself, I was very struck by this "filling in" business. The first thing that struck me was when I was in hospital and I could pay more attention to these things -- perhaps too much attention. But the scotoma in my vision, the blind area, was almost like a window looking into a landscape. I could see movement, and people, and buildings in it -- things like those my brain concocts while I'm falling asleep or before a migraine. But this seemed to be going on continuously...

But this sort of thing really only hit me after I had been lasered in June of '07 and lost my central vision. Then the night I took off the bandage, I saw this great black amoeba -- this thing shaped like Australia -- but when I looked up at the ceiling, it immediately disappeared. It turned white and became camouflaged by taking on the color of its surroundings. I then found that I could fill it in with simple patterns, like the repeating geometric pattern on my carpet.

Read the full story at NeuroTribes at PLOS.