The surface of the retina of the eye extending from the fovea to the peripheral retina detects (or is “dimensionally tuned to”) only three wavelengths that correspond to what Young over a hundred years ago discerned to be the “primary” colors determining that vision was trichromatic. In physics terms the light detection sites on the retinal surface that accomplish this are the center-to-center spaces between adjacent receptors where light is absorbed as the wave of classical physics. The lateral dimension of cone and rod receptors then has a spatial, dimension-controlling function. In physics terms these sites act as “quantum-confined electron” spaces. Light interaction with the retina can be viewed either as a classical or quantum event but it is clear that the eye fundamentally evolved to detect light as a wave. The function of the various rhodopsin complexes within receptors is to act as dimensional spacings in the process of conducting wave absorbed light energy to the signal-producing retinal molecule within the body of receptors.
It is then seen that the retina should be viewed abstractly as an array of quantum confined electron sites whose spacing has been determined by an elemental rule of geometry.
The three absorbed wavelengths to which the retina is sensitive are seen to have been refracted by the lens of the eye in an effect that has historically been termed an optical “aberration” – precisely “longitudinal chromatic aberration”. This is not arm waving! The geometrically defined light detection pattern on the retina defined by this work finally explains Osterberg’s historic 1935 measurements of the distribution of cone and rod receptors on the retinal surface. The long held view that it is different pigments within receptors that determines wavelength discrimination is shown not to be valid. No “laboratory spectroscopy” concept need be conjured up – nature employs the simplest principle of geometry to code for the refraction of light through a condensing lens. One can almost imagine at some primordial time the evolution of the eye as the result of solar radiation transmitted through a drop of water in contact with self-assembling polar long carbon chain molecules – and, over eons of time, this fundamental retinal structure evolves!
The eye geometrically encodes the physical laws of the refraction of light - nothing more!
(The referenced geometric principle can be stated as simply as “an admixture of circles of two diameters results in three center-to-center distances”. It is these three distances that correspond to the primary colors. On the retina these two circles correspond to the diameter of the cones and rods, and, moreover, the ratio of their diameters of 1.8:1 corresponds to the bandwidth of visual response).
This explanation also asserts that the precise long (R) and short (B) wavelength limits of visual response are determined by the lateral cone-to-cone and rod-to-rod dimensions. But more importantly, the concept provides a geometrically determined center (G) wavelength determined by the cone-to-rod dimension. This is the fixed reference point that Edwin Land brilliantly deduced from external color vision measurement must be present. The many hues of color that we see will be found to result from the eye comparing intensities (Land termed them “lightnesses”) on either side of this fixed reference. It can now be seen at last that Land’s color vision theory is valid!
Additionally it is shown that these light responsive retinal outer segments detect both the traditionally assumed intensity of these three predetermined wavelengths but also, and crucially, light phase information. What the three geometrically determined retinal receptor regions actually encode are intensity and phase information of these three predetermined wavelengths or primary colors.
The ability of each receptor apposition light detection site on the retina to detect both light intensity and phase proves that the Fourier equation is operative, a finding that has fundamental meaning to understanding of vision. The diffractometric (and not “photographic film-like”) retina is then actually the focal or Fourier and not the intensity sensitive “image” plane of the optics of the eye. Processing of the visual image therefore involves solution of a 2-D Fourier transformation by the underlying retina/brain interface.
I believe that the rod receptors in the peripheral retina (i.e., beyond approximately twenty degrees of retinal angle), in addition to providing high spatial frequency information for the Fourier transform of the visual image, act in parallel as the “wide angle light meter” of the eye. This integrated signal will be found to control mechanical constriction of the pupil that is the fundamental light-limiting element of the eye. Again, the rod-rod apposition distance in the peripheral retina represents the absolute short wavelength limit of visual response. This wavelength at 400 nanometers is very close to the biologically-damaging UV region. An individual having smaller diameter rods (genetically determined) would potentially allow these shorter wavelengths to enter the eye – that might lead to macular degeneration?
There are many aspects of the vision process that have never been adequately explained beyond the glaring misinterpretation noted above of the asymmetric distribution of receptors on the retina. Perhaps the most important is providing an understanding as to how vision is capable of detecting single light quanta (photons). This represents an extraordinary capability that is not currently possible in the field of photonics even using the most advanced methods that require either cryogenic cooling of the detector or use of very high electronic values of electronic amplification to detect single quanta. Neither of these is apparent in the biological eye that goes these methods one better in detecting single quanta at elevated body temperature! I have proposed that, following the realization that the eye is composed of approximately one hundred million individual receptors per square centimeter, an assumption that each retinal light detection “device” (or “receptor apposition”) acts independently leads to an understanding. These nanometer dimensioned structures operating in the very fast (femtosecond or 10-15 second)) time domain that seems never before to have been considered is the factor that reduces signal-obscuring electronic noise. Taken together, this posits that the process of vision really lies in the spatio-temporal domain of quantum physics and any further insights into the process are going to require application of this disciple of physics.
I would refer the reader to a comment that I have previously posted On the Quantum Limit Sensitivity of the Eye that discusses in more detail the above ideas.
GCH
11/12/07
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