What Do You Think You Are? by Brian Clegg

Author:Brian Clegg
Language: eng
Format: epub
Publisher: Icon Books Ltd
Published: 2020-04-09T16:00:00+00:00

THE DOUBLE-DEALING BRAIN

The brain cheats a lot. This is particularly obvious when we compare our visual image of the world with what’s really happening out there. We tend to think of what we see as being a biological equivalent of a camera. The lens at the front of the eye projects an image onto the sensors in the retina, just as in a camera the lens throws an image onto an electronic sensor. Then the rods and cones in the retina, with their optic nerve connections to the brain, assemble a picture. But just as the camera doesn’t actually store an image like a physical photograph, but instead holds a collection of zeros and ones representing the scene, so your brain does not project the view onto some kind of internal screen to produce the nice, clear image you appear to see in front of you.

In reality, the signals from the rods and cones in your eyes, funnelled through the optic nerves, are picked up by a series of modules that do things like separate out shapes, deal with blocks of colour and so on. This explains why what you see is deceptive. One obvious example is the fact that there’s a blind spot on your retina where the optic nerve connects to it. But you don’t see that gap – the brain fills the image in for you. Similarly, your eyes are regularly darting about in very quick little motions called saccades – but your brain irons out the motion-sickness-inducing jerkiness and provides a totally fake still image.

The disconnect between the imagined way our eye–brain combination works and its real mechanism accounts for the wide range of optical illusions that have been produced. There’s a beautiful example in the so-called chessboard illusion,§§ where two apparently very differently shaded squares are actually identical.

The chessboard illusion. Although it is hard to believe, the square marked A and the square marked B are the exact same shade of grey.

Image by Edward H. Adelson

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