The Brain 113
Penrose Steps
Optical Illusions
This picture is an illusion that plays with your stereoscopic synthesis. The dots appears to flip between black and white. Other illusions play with depth perception. The Penrose Steps are a type of illusion that tries to build an impossible physical model in our cerebral cortex. The brain sees perspective and depth perception cues, but the resulting shape could never exist.
Hearing Unlike sight, hearing is an absolute sense. Our ears capture and focus sound down to the eardrum where a set of small hairs called cilia convert it into electrical impulses. The impulses stimulate cells corresponding to specific pitches.
We are born with perfect pitch, yet most of us lose it early on. When I hear Maria Carey sing a top B flat a specific set of neurons located near the ear fires, and if she sings a top ‘A then a different clump of neurons are stimulated. By the time most children come to learn music they have edited out this absolute pitch information. One group of children who do not lose the ability are Chinese pianists. Because Chinese is a tonal language — where the pitch of words affects their meaning — and because
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