Saturday, January 19, 2013

Moon Illusion

Presented another answer to the age old question of why the moon comes into view larger close to the horizon than at the pinnacle.

Joseph Antonides and Toshiro Kubota from Susquehanna University (USA) re-opened the debate around the famous optical illusion. According to their theory, the illusion is due to inconsistency between the estimates of distances, which allow the brain is subjective picture of the world and according to binocular vision.

The fact that the increase of the moon on the horizon - that illusion, but not the visual effect is not disputed. That there is a lot of photographic evidence: a picture with regular camera setting moon does not change its size all the way from the zenith to the horizon. It remains an open question about the causes of this illusion.

Perhaps the best-known explanation is based on the assumption that the angular size of the moon is seen in comparison to the background of it located on the objects. The moon on the horizon involuntarily compared with objects known to us (and considerable) size (trees, buildings, etc.) and seems to be "bigger than big." A similar effect is known Ebbinghaus illusion.

Antonides and Kubota indicate two flaws in this theory. First, in all experiments with the Ebbinghaus illusion, observers reported a 10% bonus to an apparent increase of the object, and the moon can "grow up" and half. Second, it does not explain why the effect disappears in the photo and video, as opposed to Ebbinghaus illusion, which is easy to capture.

The new theory is based on the assumption that the brain evaluates the distance in two different ways. The first - on the basis of images provide by binocular vision. The smaller the difference between the projections of the image on the retina of the left eye and right eye, the more distant the object is professed. The second - on the basis of "built-in" picture of the world: for the visual cortex there is no concept of "infinity" and the brain is trying to recognize the sky as a sphere remote from us for some (albeit long) distance, with placed before her the moon, sun and stars. Here and there is a contradiction: binocular vision says that the moon did not closer than the "celestial sphere". The brain resolves this conflict by increasing the projection of the moon, and this distortion is shown, the stronger the less conventional distance to the "celestial sphere." And the presence of the horizon of the same buildings and trees causes the brain to "tie" them sky this is the house, and immediately behind him - "celestial sphere". Therefore the moon appears larger than the zenith. When we look up, the sky is perceived as extremely remote.

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