The eye views images upside down in the manner of a camera lens, but our brains reinterpret this input to allow us to see things the correct way up. Have there been any examples of damage to this part of the brain causing people to see the world upside down? How does this happen, is the brain able to compensate and, if so, how?
鈥� There is no example of damage to the brain causing people to see the world upside down. This is because the image itself doesn鈥檛 actually transfer directly to your brain; only a series of electrical signals is carried there.
The lens of the eye does focus an upside down image onto the retina. This image is then translated into a series of electrical signals which travel down the optic nerve and pass through the lateral geniculate nucleus 鈥� a kind of way station 鈥� into the occipital (visual) cortex at the back of the brain.
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The reason that the upside down image does not get flipped is because there is no image to flip. In your brain there are only electrical signals being sent from neuron to neuron, transforming as they go. Your brain processes these signals to create your experience of sight.
Experiments show that if imagery received by the eyes is inverted for a long time, these signals are simply reinterpreted by the brain and eventually perceived as the right way up.
Gregory Szucs, North York, Ontario, Canada
鈥� The brain does not need any special mechanism to compensate for the image in the eye being upside down. Once the retina has converted the image into neural information, the physical arrangement of the information is arbitrary.
For example, why should it matter to the brain cells dealing with the top half of the visual world that the nerves supplying them with information happen to originate in the bottom half of the retina?
Tim McCulloch, Camperdown, New South Wales, Australia
鈥� As a child, I remember constructing a using toilet-paper rolls and tissue paper as the screens. I placed it against one eye and covered my other eye. These lenses invert the image of the world, and initially it was very disorienting seeing everything upside down: I walked into doors and collided with any number of household objects. However, tactile feedback is a good teacher, and I learned to cope with it. After some time, my brain adapted and the image I was perceiving reverted back to normal. Then, of course, once I had adapted, taking the lens off caused everything to flip upside down again, until I readjusted once more.
鈥淚 wore lenses to invert the image of the world and after some time my brain adapted. Taking the lenses off caused everything to flip upside down again鈥�
I guess that the ability of the brain to cope with an inverted view of the world would be similar to coping with a mirror-image view: at first, trying to correctly position something while looking in a mirror is very difficult, but with practice it becomes instinctual.
Simon Iveson, Warabrook, New South Wales, Australia
鈥� It is generally known that our eyes form an inverted image of what we see and that the brain corrects the scene to look the right way up. However, when people wear inverting spectacles so that a scene is inverted before it enters our eyes, the wearer should see the world inverted. did this experiment in 1897 and claimed that the world looked the right way up again within a week. In other words, the brain 鈥渞einstated鈥� upright vision.
The experiment has been repeated a few times since, with mixed results, so the jury is still out on this claim. Experiments in the 1940s and 1950s showed that human subjects managed to ride bikes and to go skiing while wearing inverting spectacles, suggesting that they were seeing the world the right way up. However, in the late 1990s a team led by David Linden refuted this claim in Perception (vol 19, p 469). Their paper suggests that those wearing inverting spectacles simply adapt to seeing the world upside down by learning new motor patterns and increasing their skill at spatial transformations.
Mike Follows, Willenhall, West Midlands, UK