Retinal Prosthesis Dissertation - Student Home Pages

3.5 Human visual processing
Humans are trichromats i.e. the vast majority see in colour by the retina responses to
the colours red, green and blue. However upon leaving the retina via the optic nerve
(composed of 1.2 million nerve fibres) 80% of those fibres are tailored to accept
colour output from the retina in terms of three colour signal ranges historically
termed red, green and blue. The red cones respond maximally to 558nm but cover
the red wavelength (630-700) nm The green cones respond maximally to 531nm but
cover the green wavelength (520-570) nm and also the yellow wavelength of
580nm.The blue cones respond maximally to 420nm but cover the blue wavelength
(450-495) nm. [193] Rods respond maximally at 491nm. Figure_5 illustrates the way
the four colour opponent theory; operating inside the retina; is construed to operate
to achieve the three colour signals (RGB) leaving the retina at the ganglion cell
axons. [12]
Figure 4 depicts two channels of colour information: one channel carrying data
derived from the L (long wavelength (red)) and M (medium wavelength (green))
cones of the retina i.e. red and green signals and one channel derived from the L and
M and S (short wavelength (blue)) cones.
So the red (modulated by green) half channel propagates its signals down each of
the nerve fibres (ganglion cells) tailored to accept red signals and the green
(modulated by red) half channel propagates its signals down each of the nerve fibres
tailored to accept green signals The blue (modulated by `yellow’) half channel
propagates its signals down each of the nerve fibres tailored to accept blue signals.
The remaining half channel propagates a `yellow’ signal to koniocellular ganglion
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