The Standing Invitation

A Few Comments On Your Wallpaper

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Here’s another one drawn from Dennett’s Consciousness Explained. Before reading on, find yourself a pack of cards. Go ahead, I’ll wait.

Got the cards? Obviously you found them using your eyes. Human vision is pretty good for mammals. Reflect for a moment on how much detail you can see right now: you see a whole page of words, on your computer screen, in full colour. Probably you are aware of what objects are behind your monitor, colour the wallpaper is, what its texture is. It’s pretty impressive.

Now take your pack of cards, shuffle them and select one at random without looking. Keep your eyes focused on one point directly in front of you. Without turning your eyes to look at it, hold the card at arm’s length to one side, with the picture-side turned towards you. It’s in your peripheral vision. You probably can’t see it very clearly, and have no idea what card it is.

Now move your arm a few degrees closer to the centre of your field of vision. Can you identify the card now? Can you even see what colour it is? Move it a little closer. Black or red? Face card or number? Keep moving it closer, without looking directly at it. It really is surprising how close it has to get to the centre of your field of vision before you can confidently identify it; up till then, it’s a blur.

The clear patch in the centre of your vision corresponds with your fovea, the densest concentration of rods and cones in your retina. This is the only part of your eye that can see in detail and colour. The rest is devoted to picking up motion, change; it is the early warning system that tells you where to point your fovea.

You don’t see the world. You see a description of the world that is provided by your eyes. Your fovea flicks from one point of interest to another, gathering information with which to update your brain’s virtual-reality reconstruction of your surroundings. The brain’s editing process is seamless: it’s only when you deliberately prevent your eyes from moving that you realise just how patchy your vision really is.

Dennett goes further: imagine you have some really garish wallpaper, in the style of Andy Warhol, that consists of thousands of identical pictures of Marilyn Monroe. When you look at the wallpaper, how much of it do you really see? Every Marilyn in detail? Or does your brain just ‘fill in’ the rest, based on inspection of one or two. Either way, you can’t tell the difference.

The unsettling conclusion of all this is that you actually perceive the world in more detail than your eyes are providing. The sense of vision is not a window on the world: it is a cobbled-together bag of cheats, tricks and shortcuts. Fortunately, this seems to be enough.


Written by The S I

July 18, 2011 at 8:05 pm

Posted in Science

Tagged with , , ,

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