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When I take off my glasses, the world suddenly becomes a much more interesting place. A few nights ago, I was a passenger in the car, heading home late at night. It was foggy; my eyes were tired. Thinking about rubbing them, I removed my glasses when... who are they? A string - a peloton - of tiny metallic silver men on bicycles appeared, weaving across the road in front of the car. That's it, I said; I'm wearing the contacts from now on.
The point of the story is that, rather than simple blurry vision, I had a detailed vision of something that wasn't there. If I were inclined to be superstitious, I would be asking what it all means - but since I'm not, I looked it up. It means this: the human brain devotes almost a third of its power to the visual sense, but that power is mostly expended, not on recording, but on interpretation. Our eyes are, anatomically, parts of our brains, extruded through small holes in our skulls to meet the world head on - and the basic light information gathered by them, blurry or clear, is quickly assessed at progressively more and more abstract levels.
There are neurons that fire only when we see a face - or think we do in a pattern of leaves or clouds. Further neurons only fire at the sight of a face from our own species. Yet further neurons only fire at the sight of a human face we recognize; the research that identified these found brain cells devoted uniquely to the faces of Halle Berry and Jennifer Anniston.
Quirks in this visual system explain why we all fall for the same optical illusions (you can see some of the best here), but they also reveal why some of our false perceptions can seem so real and detailed. If, though some chance electrical fault, your Halle Berry neuron fires when you see someone else, you will believe it's her - your brain has no way of telling the difference. Similarly, if you "see" a spectre, a huge ape, or a figure of religious devotion, the experience will feel just as real as if those beings were right there in front of your eyes. Seeing is believing - it's just not necessarily reality.
Why should our visual systems fool us this way? Because our brains are trying to do the best they can with limited resources. Each eye produces a data stream equivalent to an Ethernet connection – and even this represents a drastic slimming down of the available optical information. The brain, though amazingly complex, is very slow: it can only manage 200 sequential calculations per second. It needs to make assumptions so we can make decisions, This means that most of our perception of the world is actually an executive summary, manipulating mental symbols we have created to stand in for real things.
The brain isn't a truth seeker; it's an explanation generator. Its optimized parameter is speed, not accuracy – because in a world full of predators, it's better to be wrong than lunch. Our illusions therefore tend to be about animate beings - humans and animals - because our most primal fears and hopes involve them.
And what about the tiny bicycles? I have no idea - you'll have to ask my brain.
If you enjoy similar tales of human fallibility, you can a new one every day on my sister site: see you there.
