Abstract
The visual system continually adjusts its sensitivity to the statistical properties of the environment through an adaptation process that starts in the retina. Colour perception and processing is commonly thought to occur mainly in high visual areas, and indeed most evidence for chromatic colour contrast adaptation comes from cortical studies. We show that colour contrast adaptation starts in the retina where ganglion cells adjust their responses to the spectral properties of the environment. We demonstrate that the ganglion cells match their responses to red-blue stimulus combinations according to the relative contrast of each of the input channels by rotating their functional response properties in colour space. Using measurements of the chromatic statistics of natural environments, we show that the retina balances inputs from the two (red and blue) stimulated colour channels, as would be expected from theoretical optimal behaviour. Our results suggest that colour is encoded in the retina based on the efficient processing of spectral information that matches spectral combinations in natural scenes on the colour processing level.
Highlights
One of the strongest visual perceptions we have is that of the different colours in the environment, from the greenish hue of the forest to the bright colours of ripe fruit
We found that colour contrast adaptation begins in the retina, where adaptation to colour can be understood in terms of two working components
The second component controls the two-dimensional nonlinearity function that translates the output of the linear filters in each of the colour channels to the firing rates of the ganglion cell
Summary
One of the strongest visual perceptions we have is that of the different colours in the environment, from the greenish hue of the forest to the bright colours of ripe fruit. Ganglion cell firing rates are matched to the mean or median of light intensity [7,8], and to the range of intensity fluctuations around the mean [9,10,11] This adaptation to the nature of the fluctuations around the mean light, or ‘‘contrast adaptation’’, implements a gain control mechanism. It decreases the firing rate response to stimuli and prevents saturation of the ganglion cell response [12] This adaptation mechanism is the result of retinal circuitry, since previous studies [13,14,15] have shown that photoreceptors do not adapt to light level contrast
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