Perception is reconstruction

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One coloured patch looks orange and the other looks brown but they are, in fact, physically identical colours. That is, each patch reflects exactly the same wavelength of light.

This illusion is created in our brains, not in our eyes. The eye treats the two coloured patches as identical, but the brain created an alternative interpretation of these colors using other information that is available — such as the pattern of shading on the cube. There is a part of the brain, called V4, that is responsible for our conscious perception of color.

[Source: PsychologyPress You Tube channel]