The eye as an active rather than a passive element
March 22nd, 2005 | No Comments »I proposed, almost parenthetically, that it follows from my concept that the eye may not be the passive “image accepting camera” that has been for so long assumed. A fundamental characteristic of light wavelength sensitive antennas, an array of which I propose forms the retina, is that they are conceptually able to transmit (i.e., radiate) as well as receive electromagnetic (light) signals. Further, from a physics viewpoint, I have proposed that the retina acts as a phase conjugate mirror (PCM). This follows from my assertion that each receptor pair or, as I define, “detection element”, decodes both light intensity and phase of incoming light rays. The property of a PCM is that it re-radiates an optical signal back along the exact path (to it’s source) upon which it entered the eye. This conceptually forms a “two way” link or a “connectedness” between source (the external perceived image) and the retina/brain. Alternatively, it may be that it is the brain that initiates the process that we term vision (”active vision”) and that this may bear on the subject of consciousness. One might see here an analogy between the brain/eye as I propose it and a “radio transceiver” … .a system that “interrogates” rather than “accepting” external reality. One might also reconsider the cochlea of the ear (also known to function in the Fourier domain) as a similarly active element. It is currently thought that “oto-accoustic” auditory emissions emanating from the cochlea are a result of external stimuli … .but… might they have… along the line of thought proposed here… a more primary role in an again “active” hearing function?… again, the ear as “radio… “?
Phase conjugate mirrors are much stranger than I can relate here… and I suggest that the reader study their characteristics (see references below) . One term used in describing PCM’s is “time reversal”, i.e., the reflected wave in retracing it’s exact entrance path “erases time” in the process. This conjures up many thoughts and possibilities in considering the process of vision!
See “How This Idea Developed - A Brief History” that describes how the “light antenna” approach to the interaction of visible light with matter initially came to my attention.
It is becoming apparent how the current interest in nanotechnology development is validating this light interaction concept. See the 9/24/04 issue of Applied Physics Letters where a group at Boston College has fabricated “antennas for visible light” (their term) from carbon nanotubes. One will note how this array resembles as to orientation and aspect ratio the receptors of the retina of the eye.
The solid state physicist will note how the “array of antennas” of the retina resembles the “pillar and pore” nanostructure of visible light interactive “porous silicon” that was discovered only a decade ago in England. I propose (and have demonstrated experimentally) that the same light interactive mechanism operates here, i.e., a classical wave interaction between two uqantum confined electron spaces. This image showing the nanostructure of porous silicon produced by Sailor’s group at UC/San Diego of the nanostructure of porous silicon.
Note how much it resembles the receptors of the retina (the aspect ratio of PS is only ~20:1… retinal receptors display a similar ratio of ~50:1).
I became interested in applying the antenna concept to the retina of the eye in 1991. I am a physicist so my first thought was to find an overview of the vision process from perhaps an optical engineering or image processing viewpoint … essentially summarizing how the eye forms an image and perceives color. I have never to this time been able to find such an overview. But what became apparent from a study of vision literature was a seemingly inconsistent (even incoherent) description of the vision process. Vision texts are replete with the “inverted arrow” diagram purporting to show that the retina forms the “image plane” of the optical system of the eye. The image plane is the plane at which film is located in a camera… therefore giving the idea that the eye must be the analogue of a camera. If this were true, however, the plan of cone and rod receptors on the retina would in some way be analogous to photographic film (or color film) or to the screen of a cathode ray or LCD screen, i.e., it would be composed of what would have to be an essentially uniform array of picture elements (pixels) sensitive to the primary colors (as on the computer screen that you are viewing). But this requirement didn’t seem at all consistent with the historically measured arrangement of rod and cone retinal receptors which doesn’t at all portray this view being wildly non-uniform. And then, there is the mantra repeated over and over in vision texts that “cones detect color” and that rods are “low light level black and white sensitive elements” (I remember a conversation that I had with a respected individual in the vision research field who opined that “no one believes this anymore”… but the question remained: what is believed?). I had certainly remembered, as I suspect had most scientifically interested individuals, the widely publicized, anomalous color vision experiments that Edwin Land conducted in the 1960-70 time frame. My thought was that these experiments would certainly have been explained in the intervening years. I found, however, not only had they not been explained, but Land’s name rarely (and strangely) seldom if ever appeared in texts or literature on vision and the eye. Another fascinating area of study was a comprehensive review of the Nobelist George Wald’s work. Wald was an excellent experimentalist who accepted the “standard” model (i.e., that three retinal cone pigments exist, etc.). In many instances, however, his findings could not be made to fit that model. For example, he found and reported that the all-cone fovea was “blue blind”, i.e., insensitive to blue wavelengths, apparently contravening the existing paradigm.
In fact, his Nobel lecture very surprisingly agrees with the model that I arrive at, wherein he presented a plan of light interaction with the retinal surface that is in almost exact agreement with my findings! It was for these reasons and much more that I was motivated to arrive at the concept that I propose. I believe that my model of light interaction with the retina and the resulting vision process that it describes fits existing data much better than the incoherent picture historically presented in the literature of vision. One area of particular interest is my contention that three “classes” of cones and, particularly, that blue-sensitive (or “S”) cones do not exist (see comments). I welcome discussion and argument regarding my thoughts below in the comments area.
From a physics viewpoint it is crucial to understand the concept of a “nanowire” (see definition and discussion below). The retina of the eye should be viewed as a specifically ordered array (a “forest”) of vertical, high aspect ratio nanowires that evolved to detect the spatial Fourier transform of the visible spectrum. It is as simple as this. Light interacts as a wave in the three discrete geometric spacings (i.e., cone-to-cone, cone-to-rod, and rod-to-rod) that the retina defines between any two nanowire/receptors. These light interaction “centers” act as “light antennas” that are narrowly tuned on the retina to only three specific wavelengths (or colors)… and these are what we have termed the “primary” colors.
