I. Western Science
How light becomes sight (the very brief version):
1. Light, in the form of photons, contacts receptor cells on the rods and cones of the retina of the eye.
2. Through various electrical and chemical processes, these impulses are transferred (at points being rendered upside-down, and crossing over, left to right, and right to left) along the optic nerve into the part of the brain called the thalamus.
3. These impulses then make their way to the visual area of the occipital lobe of the brain. This is where what we experience as "seeing" begins.
4. In the temporal lobe of the brain the impulses/images are interpreted in the context of various associational networks, producing the rich and textured experience of what we call our "vision."
From Swami Savitripriya's translation/commentary on Patanjali's Yoga Sutras (III: 21-22)
"Through the practice of Becoming the Object of the point where the light that is reflected off of the physical body you are looking at meets your eyes' power of perception, you will be able to suspend your visual awareness so that any object, or portion of any object, will dissolve and disappear from your sight; enabling you to look into, or through, any gross physical form.
This explains how you can also suspend awareness of the sensations of sound, taste, smell and touch while you continue to remain involved in outer physical activities."
Lila is a standard poodle -- curly-black fur, a prancing bundle of excitement and joy - who I periodically take walks with. Lila's human is my friend Deborah Fryer, a brilliant film-maker whose artistic eye is truly sublime. Check out her work at Lilafilms.com.
It may be true that what we see is already gone, but somehow it seems true, also, that - at least potentially -- we have a hand in creating what we see, as a film-maker does in creating her or his films; or a yogi in choosing what layer of the visual universe to perceive, at any given moment.
By the way: the image above is comprised entirely of straight lines -- your ruler (friend or foe?) will prove it, even if your eyes can't.