Rods and Cones

120 million rods, but only 5, 6 or 7 million cones (depending who you read) in each human eye, the cones concentrated in the fovea centralis, the 0.3mm pit at the focus of the lens. The rods are more sensitive, accented towards blue-green, night vision, motion sensing, peripheral visionand reds ths appear blacker at night. They have a tendency to burn out in bright light. Cones specialise in the RGB range, with an overlap between 'red' and 'green' receptors in the yellow range, which thus appears brightest.

Materialist accounts of light should span the scale from quantum optics to physical optics (refraction etc), and thence to physiological optics and to the brain's handling of light. This scale begins and ends in mystery.

But perhaps there is something to add, in the thesis of the social construction of science as discourse – a process that materialism has its hand in – and in the social nature of perception. The latter emerges from the relative inability of stereoscopic vision to give a clear sense of distance, which requires two pairs of eyes or more to triangulate fully, which in turn may be why, when we see someone staring intently towards something, we follow their gaze to see what they see.