As David Hockney put it, “Drawing makes you see things clearer, and clearer and clearer still, until your eyes ache.”
Seeing begins with opening an eye to light. I don’t understand what it means for light to be a wave and a particle, but I have seen white light refracted into a rainbow, which helps me understand that the light we see is just part of a larger invisible spectrum. For example, there’s ultraviolet light, which I’ve heard that bees can see, and infrared light, which I imagine as being like the dim glow of the nocturnal reptile house at the National Zoo, humming and warm. Light (of all kinds) enters our eye through the contracting pupil, focused by a sliver of lens, and touches the retina in the eye’s rear curve.
In the array of cells at the back of the eye, two main types of receptors respond to the light, beginning the process of converting light energy information into electro-chemical information that can move through the nervous system. Rods, the first type of receptor, are sensitive to contrast and motion. They can function under low light and are concentrated in the peripheral areas of vision. Cones, the other type of receptor, are sensitive to detailed information and color. They are most effective under high illumination, and are concentrated in the central point of vision—the fovea.
Information from the responses of these photoreceptors passes to bipolar cells. For rods, there is a high level of convergence, meaning that many rods provide the input to one bipolar cell. The rods are, in this way, averaged. Although this means the “truth” detected by each rod is lost, convergence facilitates vision in low light since small signals are added together. It also enables motion detection, since movement doesn’t occur at a single point, but rather across points.
For cones, there is a much lower level of convergence. A bipolar cell gets input from one cone. The signal is preserved more clearly, retaining detail.
The responses of the bipolar cells stimulate ganglion cells. There are more than a million of these in each eye, and it’s their long reaching axons that project from the eye bundled together in the optic nerve, synapsing in the brain. From the limited sliver of light entering the eye, to the particular responses of rods and cones, to the averaging of ganglion cells, to the processing of the visual cortex, imperfect signals form the basis of our understanding.
That’s how visual information begins to move from the world, into the mind. That’s how I begin to draw.