We take it for granted that we see the world as it actually is, but in fact, we do not. Our perception of the world is the brain’s best guess at what is actually happening, based on the information it receives through the senses. Optical illusions clearly demonstrate that the brain does not always interpret sensory information correctly, by producing a discrepancy between what we see and and how we perceive.
http://www.theguardian.com/science/neurophilosophy/2011/aug/17/memory-contaminates-perception
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