The following figure showing the distribution of foveal cones is abstracted from Fig.27 of “Vision and the Eye” (M.H. Pirenne, The Pilot Press, London, 1948). Quoting Pirenne: “The mosaic of the cones in the fovea centralis of the human retina represents the bodies or inner segments of the cones arranged in curvilinear rows as a shagreen-like mosaic” (italics are mine).
Note that there are some 200,000+ cones in the fovea, that they are arranged in circularly symmetric fashion, and that they represent approximately 99% of all of the cones of the retina. Circular symmetry is thus at the heart of the vision process.
The light detection centers formed by cone-to-cone appositions in the fovea defines the ‘red’, long wavelength limit of the visual response of the eye. Since cone-to-cone distances are equal, the fovea responds to a single red wavelength (or at most a very narrow band of red wavelengths). Response to red is thus uniform across the fovea. At the edges of the fovea (at approximately one degree of retinal angle) rod receptors start to intrude on this regular cone matrix (forming ‘green’ detection centers) and causing a ‘falling off’ of red sensitivity.
As the density of rods increases, it is observed that he fovea is surrounded by concentric bands of ‘green’ (peaking at 7-8 degrees of retinal angle) and, finally, at angles of 15 degrees and beyond, to pure ‘blue’ sensitivity. These are bands of pure, geometrically-defined, wavelength sensitivity. This is exactly the retinal response that Edwin Land deduced must be operative in the discernment of color in vision. The center of the ‘green’ response at 8-7 degrees where rod density is sufficient to completely surround each cone geometrically defines the exact middle of the visual response band – 550 nanometers. No laboratory spectrometric measuring instrument is required.
As I have said, I believe that the imaging area of the retina extends to approximately 15-20 degrees. The primarily rod area beyond, I believe, forms a wide-angle ‘light meter’ controlling papillary constriction.
The retina is thus shown to be a diffractometric surface the only meaning that this can have is that the eye functions as a Fourier-transforming device, i.e., that he retina (specifically the fovea) is located at the focal (not the ‘image’) plane of the optics of the eye. I have shown that the Fourier transform of an ‘outline sketch’ is primarily a small central ‘dot’ as shown in the following figure from Caulfield (abstracted from the paper by Hagan referenced elsewhere in this work). An interpretation of this figure is that the small dot contains all of the information necessary to construct the ‘sketch’ image in both light intensity and phase form to satisfy the Fourier equation. Note, that the Caulfield figure is an ‘optical’ rather than a ‘Fourier’ transform. Optical transforms are images taken using photographic film at the focal or Fourier plane but do not encode light phase information for the simple reason that we do not possess technology to accomplish this as the eye does!
I believe that the Fourier transform performed by the fovea provides the “outline sketch” (the “Marr sketch”)of the perceived image. Since the foveal detection centers are able to process Fourier information (light intensity and phase) a complete image must result. In a sense then, the focal or Fourier plane comes into coincidence with the image plane! Remember that this image derives solely from long wavelength (red) interactions. And..I learn that this information, i.e., an actual image, is transmitted in 1:1 fashion to the visual cortex of the brain. This image, the ‘actualization’ of the Fourier transform, appears in the brain and I might propose forms the ‘basic image’ for further processing – addition of detail. color, motion, etc..
As to color I would propose that it will be found that the two other ‘pseudo Fourier transforms” that I define – the green and blue – are transmitted to the brain in the same manner and are processed to ‘overlay’ the basic sketch image. One additional step of comparative processing of the latter two transforms (around the 7-8 degree geometric center) must ensue to arrive at the hues of color in the final image. It is amazing that this scenario if it proves to be the case is the exact analogue of Edwin Land’s famous 1953 color experiments!
JUST A NOTE IN PASSING:
In reading neurobioiogical texts re: color and the brain I continually find the “where” something happens (in the brain….where color is processed etc.) but never “how” this happens..the mechanism..and there is a yawning chasm between these two descriptions. An understanding of vision in my view desperately requires input from fundamental physics and/or electrical/optical engineering. I have been amazed from the beginning of this exercise that a fundamental understanding or description of how the visual image is formed doesn’t seem to exist! It is just assumed (incorrectly) that the eye functions as some sort of ‘camera’ ..even though voluminous data taken over the years is fundamentally at odds with this idea. ????