|
 previous / next column
A PHYSICIST WRITES . . .
(March 2004)
In July last year I attempted a description of how the brain rapidly performs the complicated task of enabling you to ‘see’ what you are looking at. In brief: the tiny images captured by your eyes go through an extraordinary process of dissection, reassembly and matching against your visual memory. At the end of it, apparently without any mental effort and in the twinkling of an eye (!) you are able to identify every object in front of you, and work out exactly where it is and in what direction it might be moving.
Well, not quite. To keep the story short I missed out a couple of surprising facts. Firstly, the subconscious brain ignores a great deal of the information from the eyes, particularly if it seems confusing or unimportant. Secondly, much of what you think you see is actually being invented by the brain to fill gaps and to try to make better sense of the picture.
Let’s consider the inventing first: are you aware of the sizeable blind spot in each of your eyes? No, because the ‘holes’ are cleverly filled in with whatever colour is in view around them!
Even when you close your left eye, say, you will only notice the blind spot in the right eye if it covers some small object and makes it vanish (this will be just to the right of where you are actually looking — see my April 2003 column).
A different sort of in-filling occurs if you are on the road and the front and rear ends of another car happen to be visible on either side of your door pillar. Immediately (with luck) the brain will recognize them as a complete vehicle and you can then predict its path relative to your own car, as if it was in full view. This is not just common sense but a real achievement of brain-power.
As for the information that is simply being ignored by the brain, this was wonderfully demonstrated by a TV programme last year about vision (it was part of a BBC series exploring each of our senses in turn). Near the end of it we saw a group of people about to watch a short video of some basketball players warming up.
The watchers were instructed to concentrate on counting the number of times the ball was passed. We at home were told that a man in a gorilla suit would appear among the players, beat his chest and walk off again. But because their attention was on the ball, three-quarters of the watching group failed to notice the intruder! When the video was replayed (this time with no instructions) they could not believe their eyes.
The last laugh was against us, though, when the presenter told us that the same gorilla had appeared in the background several times during the course of the programme. Even when I viewed my recording of it again some months later — knowing he was in there somewhere — I did not see him once.
Such is the ability of the brain to concentrate on something and blind you to everything else. While you are focused on reading this, are your eyes telling you much about what may be happening around you? I suspect not.
In fact the brain would become overloaded with information if it did not work in these curious ways. But they undoubtedly make trouble for motorists.
On my route home from work I turn right and then nearly always have to work my way around a car parked immediately on the left. On one occasion my attention was so firmly on this car that I did not notice another one approaching from beyond. I saw it only just in time to avoid blocking its path — yet it must have been in view from the moment I started to turn the corner. And it can’t have been covered by the blind spots of both eyes at once!
I believe there is a serious message for drivers in all of this, especially when the view deteriorates a bit. If the traffic situation is confused, or you are driving into mist, or the windscreen steams up, or the wipers don’t clear the glass right to the edge, then road hazards do not simply become harder to see. Instead, the subconscious brain may decide to ignore the signs of a hazard altogether, probably earlier than you would expect and certainly without asking you first.
Thinking again about your door pillar separating the two ‘visible’ ends of another car, for example: you rely entirely on the brain as it first detects the outlines and then tries to decide whether they are important. The next task is to recognize them as a moving vehicle, and only then does the brain finally make you consciously aware of the hazard. If at any stage this process stopped because your attention was too much on something else, you might never know what hit you...
Peter Soul
previous / next column
|
