Tuesday, 29 November 2011

DECEMBER 12th [Science Comedy Advent Calendar]

December 12th: The Fovea

Christmas. There’s a lot more that goes into it than one person can feasibly experience. The amount of preparation involved in acquiring gifts, all that food to get, cook, and give to people who may well be too intoxicated to recognise what it is they’re consuming.  The decorations, the work scheduling to get it all organised, the arrangements, the visits. A lot of effort by one part, which may be experienced as nothing more than a brief visit and an exchange of pointless Christmas cards by another party. It’s tragic, in a way.

And that’s just on a small-scale, individual family basis. What about the industrial processes that go into the whole festive season? Christmas seems to have a profound effect on the whole economy, it’s reported in the news, with constant update son how the high-street is doing. And think of the manpower that goes into converting every branch of every multinational into a more ‘festive’ style. Even the fictional aspects, the Santa and his elves thing, if that were true, it would involve countless hours of manual (‘elf’ual?) labour and the violation of spacetime by a bearded fat man; and for what? This herculean effort is experienced by individual children as a period of excitement and the acquisition of a few more flimsy toys. Is that really all it amounts to?

This shouldn’t be surprise though, seeing as humans experience such a thing on a regular basis. Our own eyes and brains are actually capable of experiencing only a small fraction of the visual stimulus that constantly bombards us. You’d probably assume that our eyes encode the visual scene we experience in much the same way as a camera processes an image; light goes in, gets moved around a bit, then sent to the brain/film/memory card. But no, not the human eye.

When it comes to fine detail, the sort of useful, accurate, specific processing is limited to an alarmingly small area. It’s the fovea, the part of the eye that’s most densely packed with photoreceptors (only cones, no rods, by the way). It can pick up on the small details, the finer points, and no other part of the eye can. It’s like a very small searchlight casting about through the fog of our visual sensory input. What we essentially do is use the fovea to focus (no pun intended) on things which our visual systems classify as worthy of attention. Visual psychology experiments have used tracking software to follow a person’s eye movements when looking at stimuli such as elaborate paintings. It’s interesting, the tracking pattern is like someone tried drawing the painting themselves on an etch-a-sketch while suffering serious drunken tremors.

But it’s enough. The brain can take this scattering of detailed glimpses and build up a detailed and, more relevantly, useful perception of the world itself. All from a part of the retina that’s no even a millimetre in diameter. Even for something as small in area as the retina, that’s a pretty pathetic amount of space given over to detailed perception, don’t you think? Especially when the periphery of the retina can’t even encode colour (our brain just infers it later in the processing stage, if you’re wondering).

But if you did think the fovea was a measly allocation of useful processing space, look at it this way; this measly bit of retinal space is sufficient to provide us with the sort of rich detailed vision we take for granted, despite the fact that it’s mostly the result of brain processing rather than direct sensation. You want more? Well, if the fovea were twice the diameter it is, we’d actually need brains the size of beach balls to handle the data input. And that wouldn’t be practical. We’d need crackers to have paper hats that were a lot bigger (there may also be other consequences, like needing bigger wigs if you’re a bald man).

So yeah, the effort that goes into making Christmas happen is just like our visual perception; far more is going on than we can actually perceive. But what we have, that is usually more than enough.

See, I can do schmaltzy too, just so you know.

Twitter: @garwboy


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