Introduction
Light + Eye + Brain = Vision
Depending on our familiarity with the variables to the left of the equal sign, our titular equation may seem a metaphor of thin explanatory power or one with something of the compressed elegance of e = mc2. Of course, the value of the metaphor is a function of our further knowledge of the many sums and products and quotients resulting from the myriad of previously operated processes that ultimately define the variables. Use of the unqualified variable "Eye," for example, implies a knowledge of the integrated workings of the cornea, pupil, lens, rods, cones, photopigments, etc. For that matter, we could press even further into ever smaller and more fundamental components in hopes of arriving at some first material principle; but that would require us to cross the traditional boundaries "separating" biology from chemistry and physics.
So, as a matter of practicality, let us assume that we are only biologists; that chemists and physicists have provided us with certain givens; and that the somewhat larger and less discrete findings of biology are sufficient for our understanding.
We will begin, then, with a short description of the role of light in vision, to be followed by descriptions of the anotomy and physiology of the human eye. A third section will trace visual input from the retina to the primary visual cortex and, eventually--as the site is expanded--to the other cortices to which this input is later reflected. Next will follow a section devoted to invertebrate vision, the subject with which this laboratory in most deeply associated. And we will conclude with a discussion of vision.
In this last regard, please keep it in mind that vision, or an explanation of vision, is in notorious want of some “binding mechanism.” That is, we have eventually to explain how the various nuclei of the brain are able to assemble the results of various discrete processing activities into the integrated complex of the thing finally seen. But this last all-explaining activity appears, like consciousness, to be epiphenomenal—a synergistic phenomenon circumscribed by associative cortical machinations without a center. So, its explanation remains—if only for the present—as mystical as Augustine’s God cum circle.
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Note: This site was originally intended to emphasize the invertebrate visual system, which is now introduced only after a description of our own eye and brain. We thought it would be simpler first to describe a system for which you would not have to imagine the output and, then, to describe alien systems, whose contemplation would probably elicit affective misgivings in regard to their differences. It is inevitabe that they be interpreted as limitations when we attempt to imagine their eyes because it is so difficult to unimagine our own. How hard it is not to reach for the metaphors of impairment: "it is like myopia," "like a cataract," "as if it were colorblind."
Even more confounding is the consideration of the not-so-strictly-visual components of seeing. For example, when we wonder whether a fly sees the same as we do, we have, in turn, to wonder what such “same seeing” would actually mean. Humans are bound to the world by guy wires of meaning, and many things—perhaps, most—possess an emotional resonance of some sort. But does the fly have nominal categories for the various objects in its world? Would a fly linger at a scene for the thrill of merely reliving some prior pleasurable experience? Does the sight of a larva inspire it to tears in the recollection of its own larvahood?
At the risk of sounding presumptous, let's say no. Its vision may function a little more like our sense of touch—a non-primary sense, used to distinguish between the tolerable and intolerable circumstance while largely devoid of the affective frame of mammalian vision.
--But the point of this note is to acknowledge that our original ambition is not yet realized. The section on invertebrate vision has only an introduction and an apology. However, more is on its way; so, please, please revisit our site.