Friday, May 16, 2014

Ponzo Illusions and Your Brain

My brain is fascinated by illusions. Even when it knows that it is somehow being tricked, it’s still interesting. Take Ponzo illusions, for example. This phenomenon was reportedly first demonstrated by Mario Ponzo, an Italian psychologist, early in the last century. It was his opinion that the human mind judges the size of an object based on its background. He demonstrated this by drawing two identical lines across a pair of converging lines. The explanation typically given is that the upper line looks longer because the mind interprets the converging sides according to linear perspective. In this context, it interprets the upper line as though it were farther away. Naturally, most people perceive the upper line as longer because a farther object would have to be longer than the nearer object in order for both to produce retinal images of the same size. Intellectually I know that the two parallel lines are the same length. Because they are pictured against vertical receding lines, however, at first glance the two parallel lines often appear to be of differing lengths. If you haven’t looked at examples of Ponzo illusions for a while, check out this website and pay attention to what your brain perceives.

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