Thursday, 27 April 2017

An odd ghost

Sun behind treeI noticed an intriguing diminutive human figure in the street but not for long. After just a second or two it vanished! So, a ghost then! I thought it was odd, even for a ghost, and afterwards I realised why.

The figure was walking along a sunlit pavement. When I saw it, most of the figure was concealed behind a foreground tree, which was in shadow. I soon realised that the figure was a result of misperception caused by the foreground tree. But here's the weird bit. The figure was clearly sunlit while the tree was firmly in shadow. So how could that happen?

I realised that the 'figure' was actually formed by the bits of the sunlit pavement that I could see through the tree. These areas, enclosed by the branches and leaves of the tree, were united in my brain to form a fleeting human figure. It was a bit like the photo (above right) but with the bright areas suggesting a figure. The movement of the 'figure' was caused by the fact that the tree was moving gently in the wind. My brain interpreted this movement as walking because the 'figure' was apparently on the pavement.

I have come across misperception caused by shadows in the past. The enclosed areas of brightly lit pavement were similar to shadows except they are bright instead of dark. It seems human perception makes little distinction. It is the shapes formed by the shadows / bright areas and their relative positions which is vital. And in this case the light bits seen together suggested a human figure. The 'figure' vanished because the shapes moved around and stopped resembling a person. Obviously, the figure in such a situation would always appear to be partly concealed by a foreground object.

From this experience I would say that this kind of misperception can be particularly convincing. It was only when it vanished that I realised it wasn't a real person. Having said that, I did think it was an odd-looking figure at the time.

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