 Colour vision
ability to distinguish
among various wavelengths of light waves and to
perceive the differences
as differences in hue. The normal human eye can
discriminate among hundreds
of such bands of wavelengths as they are
received by the sensory cells
(cones) of the retina. There are three types
of cones, each of which contains
a distinctive type of pigment; one cone
absorbs red light, another green,
and the third type blue-violet. A given
colour stimulates all three types
of receptors with varying effectiveness;
the pattern of these responses
determines the colour perceived. In 1986
researchers identified the genes
that correspond to the red, green, and blue pigments.
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Cones
in neurology, light-sensitive neuron with a conical projection in the retina of the
vertebrate eye, associated with colour vision and perception of fine detail. Shorter
and far fewer than the eye's rods
(light-sensitive cells), cones are less sensitive to low
illumination levels and are mediators of photopic
rather than scotopic (Greek skotos, “dark”)
vision. Cones are mostly concentrated at the central yellow
body containing the fovea
(depression in the retina), where no rods are present, while at the outer
edges of the
retina, cones are sparse. Chemical changes that occur when light strikes the cones are
relayed as impulses to optic-nerve fibres leading to the occipital lobe of the brain. |