I went the other day to see the new 3-D film of Alice in Wonderland. Compared to the original it fell flat. Plenty of viewers will find itflatter, for they are stereo-blind; unable to sense depth in a scene by combining the slightly different images that come from each eye. Until they find themselves baffled by what seems like double-vision as they watch the antics of the Red Queen, most among them – like many with colour blindness – do not realise their predicament. Plenty of animals, after all, give up depth in favour of breadth. Lewis Carroll's White Rabbit,with eyes on either side of its head, sees only a small part of the world in three dimensions, but has a much wider field of vision. A panoramicview is useful when a binocular Cheshire Cat creeps up from behind in the hope of a meal.
A recent survey of thousands of fifty-year old Britons showed that around one in seven has some stereo blindness although most are scarcely aware of it. For a few the difficulty arises because they were cross-eyed in infancy, and although that was solved by surgery, it was by then too late for their growing brains to learn the difficult job of fusing two images into one.
The real Alice, Lewis Carroll's Oxford friend, was ten when the tale was first told to her so that her strange visions cannot be blamed on her early life. Babies develop some stereo ability when they are four months old. It was once thought that those who had not developed the talent within their first five years or so would never be able to do so. The good news is that with careful training, and with the use of prisms as spectacles, many adults with the problem can learn to see in stereo, putting paid to the old idea that the brain cannot be persuaded to change its habits.
Vision, like art, involves more than the physics of the eye. When the March Hare tells Alice at the Tea Party to "say what she means", she replies that "at least I mean what I say – that's the same thing". "Not the same thing a bit!" says the Mad Hatter. "Why, you might just as well say that 'I see what I eat' is the same thing as 'I eat what I see'!" To Lewis Carroll that was a joke about a then novel form of maths in which y times x gives a different result from x times y. The statement also says something about eye and brain.
Alice was the daughter of the Dean of Christ Church and of impeccably privileged background. For those of us in the real world, there is an unexpected tie between stereo-blindness and social position. People with the condition tend to come from poorer families, grew rather slowly as infants, and lived in relatively crowded conditions. As adults, they score slightly worse than average on measures of depression and of overall health, are poorer and are more likely to be single. Childhood deprivation also increases other difficulties in eyesight – but stereo is affected most of all, hinting that the problem lies in the brain and its early experiences rather than in the eye itself.
he eyesight survey shows that damage to the growing brain can change the way one sees the world, but also the way the world sees you. That sounds simple – but as usual when it comes to the contents of the skull, the Mad Hatter has something useful to say. People born with only one eye, or those who lose an eye in early infancy, have never seen in stereo. Even so, tests of those who suffer that fate shows that that many among them are as able to sense depth as are the rest of us. They do it in a different way, often because they have a much improved ability to pick up slight differences in light and shade which compensates for their lost perspective on the world. For them, life in two dimensions may be as meaningful as in three. The one-eyed men circumvent the simple logic of Alice in favour of that of Wonderland, in which causes and consequences are not necessarily related. I have vivid memories of fleeing from a cinema in the 1950s when, in a Western, arrows suddenly started pouring from the screen. It scared me so much as to put me off films for years. Now the stereo in Alice seems to me to reduce rather than enhance the magic of the tale itself (and the barbarities visited upon its plot do not help). Perhaps one unlearns the ability to see life in depth as age creeps on – or perhaps one's outlook gets flatter for other and more intractable reasons.
When watching 3D can fall flat
source telegraph.co.uk
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