Human visual system

The eye and brain pathways that turn light into perception, from photoreceptors through the lateral geniculate nucleus to the visual cortex.

Phototransduction: The biochemical cascade by which retinal cells convert absorbed photons into electrical signals. The first conversion step of the whole pipeline, inside every rod and cone.
Rod cell: Photoreceptor tuned to dim light; saturated in daylight but capable of single-photon sensitivity. Rods carry night vision and dominate the peripheral retina.
Camera obscura: A dark chamber projecting an image through a pinhole or lens, the historical model of passive optics. The eye's optics resemble a camera, but the brain's processing diverges from any photograph.
Optical illusion: A stable, shared mismatch between the visual percept and physical reality, exploited to probe visual processing. Illusions expose the shortcuts and assumptions the visual system makes.
Hermann von Helmholtz: Nineteenth-century physiologist who measured the eye's optics and founded perception-as-inference theory. His Handbook of Physiological Optics set the agenda for two centuries of vision science.
Retina: The layered light-sensitive tissue at the back of the eye where photoreceptors and retinal neurons process images. The retina does substantial computation, not just detection, before signals leave the eye.
Cone cell: Photoreceptor operating in bright light; the three cone types underlie human color vision. Cone types and their dense packing in the fovea set the limits of daylight vision.
Computer vision: The engineering discipline of extracting meaning from images with algorithms and learned models. Machine systems mirror human visual tasks while failing and succeeding in different ways.
Blind spot: The retinal region lacking photoreceptors where the optic nerve exits, normally filled in by the brain. The optic disc's gap proves perception is constructed, not a literal image.
Hubel and Wiesel: The neurophysiologists who recorded single cells in visual cortex and mapped orientation columns and critical periods. Their decades of V1 recordings won the 1981 Nobel Prize and defined cortical vision research.

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