optic chiasm

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An area at the bottom of the brain immediately below the hypothalamus where decussation (partial decussation in humans and other animals with forward-pointing eyes and therefore overlapping visual fields) of the optic nerve fibres occurs, with approximately half the fibres from each eye (the fibres from the nasal retina of each eye) crossing over to the opposite cerebral hemisphere. The effect of this is that images from the left visual field of both eyes are transmitted to the right cerebral hemisphere and images from the right visual field to the left cerebral hemisphere, enabling information from corresponding points in the visual fields of the eyes to come together in the visual cortex for binocular depth perception. In animals such as rabbits with much smaller overlap of visual fields, almost all the fibres are crossed. Also called the optic chiasma. See also binocular cell. [From Greek optikos optic, from optos seen + chiasma a cross, named after the shape of the upper-case letter chi (X)]

Subjects: Psychology.

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