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Colour vision refers to the ability of the visual system to perceive wavelength of light as colours. It is dependent on retinal cone cells, which express photoreceptors that are sensitive to specific wavelengths of light.
A long-standing puzzle has been the seeming inconsistency between neuronal responses in primary visual cortex to colored stimuli and the elementary perceptual attributes of color vision. Nonlinear analysis resolves this paradox.
The diverse population of retinal cell types has now been shown to include one that does a neat trick: an interneuron inverts the sign of the retina's response to blue light, creating the blue-Off output signal to the brain.
How do we tell red from green? Work on the primate retina shows how neural circuitry combines signals from individual cone photoreceptor cells to provide the basic building blocks for colour vision. See Article p.673