The retina (the light-sensitive portion of the eye on which an image is formed by the lens) contains two classes of photoreceptors (rods and cones) that are interconnected by a complex network of neurons which feeds into the optic nerve connecting the retina of the eye with the visual cortex of the brain. Rods (so named because of their long rod shape), which are located outside the fovea, are much more sensitive than the cones, and serve night vision. But they all have the same photopigment and, acting alone, cannot mediate color vision. In contrast, cones (so named because of their short cone shape) are located predominantly in the fovea, are less sensitive than the rods, function best in bright light, and serve fine pattern and color vision. (There are, in fact, three types of cones, each of which responds more to a different color group--the reds, the blues, and the greens--rather like the component colors in a television set.)
There are four principal implications of this information for Bonnard's paintings: (1) The appearance of those parts of the paintings seen in peripheral vision; (2) The appearance of the paintings under varying light levels; (3) The varying appearance, under varying light levels, of long- and short-wavelength spectral colors; and (4) Bonnard's manipulation of the gaps in the perceptual chain.
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