November 15, 2007

Brain Sees What The Eyes Can Not Behold:The Strange Facade of Optical Illusion

card showing misspelled textIf you look carefully at the image on the left and read the text aloud, chances are that you will read this SMS type text just as gracefully as you would read ordinary texts. Despite the several spelling mistakes that the eye detects, the brain comes in to fill in the void, by its own damage control machinery. Optical slips are also managed in more or less the same way when we see TV or watch a movie, which are typically delivered in frames per second.

There is no denying the fact that the physiology of visual sensation itself is interesting. Hyperpolarization of photoreceptors plays important role in the propagation (generation) of nerve signals. It is in stark contrast to what happens normally; depolarization of cells as a means of signal generation and propagation. Moreover, the image retina gets, as a result of light passing through the lens, is an inverted real image. But we see them normally, not upside down, as a result of some manipulations by the brain.

autostereogramThe picture on the left is an example of autostereogram. This is a FANTASTIC picture! Just save the picture in your computer, then open it using Windows Picture and Fax Viewer. Look at it but don't focus on the plane of the picture! Easier said than done. Now try to adjust your focus back and forth; a picture of a 3 dimensional ball will begin to emerge. Concentrate on it. When you can behold the image relatively easily, for a longer period, zoom in on the image, using the scroll button of your mouse. A brilliantly colored spirally twisted cone will advance towards you, perpendicular to the plane of your computer monitor's screen. Its really tough, initially, but exercise your patience, you will get the experience of your lifetime. You can see some more of these stereograms here.

Many other interesting optical illusions are there, and some even take into account, the 4th dimension: the images move. You can get some of them here. However, sometimes the eyes see right but the brain goes bonkers. In the extreme example of visual illusion, one interprets a coiled rope for a snake. This may have been the result of the survival advantage it offered, which we acquired in the course of evolution. So, trick the eye and fool the brain.
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