Size Constancy (Plummer)

Size Constancy is the mind's proneness to percieve a particular familiar object as larger than another because of differences in distance. It is similar to depth perception. The visual system will often exploit regularities from the environment when it determines size and distance relationships, meaning that your mind will accept a clearly impossible size difference instead of noticing the environment. The photo below depicts two dogs of the same size, however it initially appears that the dog farthest from us is larger.

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