Perhaps a Yet Simpler Explanation…and more about Land

by Gerald Huth on June 10, 2006

A correspondent has pointed me to a beautiful book by Oliver Sacks “An Anthropologist on Mars” that describes the case history of an artist who, after an auto accident, and although retaining vision (with perhaps increased acuity), lost all sense of color. It is a fascinating tale, of which I will write about shortly, but it goes a long way, I believe, toward substantiating Land’s work and my subsequent corroborative explanation of the vision process. The author recognizes Land’s genius and understands well his color vision concept even terming certain brain functions ‘Landian’ (p.39, “…another part of the brain to perform the requisite Landian correlations). According to the author, this individual’s injury was to one of the locations in the brain that processes color visual information, but it was the character of this information from the eye that led to this understanding. Land was certainly cognizant of the linkage between retina and brain in coining his term “Retinex” (i.e., retina + cortex).Unfortunately, the only theory that he knew of to explain his experimental results was the traditional one (namely, that ‘classes of cones’ exist). He had to resort to devising an external (and complicated) algorithm to simulate the visual response that he measured. I am fascinated that the new explanation presented herein seems to me to lead to new insights regarding the retina-brain linkage in the vision process. We now know for the first time the correct content of the visual input information to the brain. I will write more about this.

It occurs to me to try again to attempt to summarize the light interactive properties of the retina. To begin, I assert that there are no ‘classes of cones’ and that three (and only three) wavelengths are detected by the three receptor appositions (cone-cone, cone-rod, and rod-rod) of the retina. As shown in the following drawing that overlays these wavelength response regions onto the classic Osterberg 1935 diagram of the density of cones and rods on the retinal surface. PLEASE NOTE THAT WAVELENGTH RESPONSE IS ACTUALLY DERIVED FROM, AND BASED ON, THE OSETERBERG DATA.
Please note that these are not the usual spectral plots but rather show (or attempt to show) variations of intensity at the same wavelength across each band. Each band is, in antenna engineering terms, ‘tuned’ to a single wavelength. It is light intensity at this single wavelength (proportional to the apposition-defined density of antennas) that varies across each band. The retina is sensitive to light intensity at each of the three wavelengths exactly as Land deduced must be the case. These three bands correspond to what have become to be termed the ‘primary colors’. The red intensity band detected by foveal cone-cone appositions is extends to a degree or so of retinal angle. This red wavelength corresponds to, and defines, the precise long wavelength end of the visible spectrum. The highest density of cone-rod appositions, and thus ‘green’ response, occurs at 7-8 degrees of retinal angle as shown.This then is a geometrically fixed point /on the retinal surface that precisely defines ‘midband’. This is the fundamentally important point that Land brilliantly deduced from external measurements must be present (his ‘fulcrum’) and which explains the color constancy of vision. By 10 degrees the blue response of rod-rod appositions becomes dominant and this response continues to the peripheral retina. Importantly again, this precisely defined blue wavelength defines the short wavelength end of the visible band. The many hued sensation that we term ‘color’ is determined by comparing light intensity on either side of the fixed midband point at 7-8 degrees. There is always a geometrically-defined wavelength reference point!

I must say again that the above defines a surface that is sensitive to the /diffraction pattern /of the perceived image. The retina must be the Fourier (or focal) plane of the eye and the image formation lies in that domain with processing occurring somewhere between the retina and the brain in a yet to be determined manner. It is conclusively shown, however, that the eye detects the 2-D Fourier transform of the perceived image (as Hagan presciently proposed). Additionally, I have described how the receptor apposition-defined ‘antenna’ detectors of the retina are able to detect both light intensity and phase that is a requirement of the Fourier equation. This realization opens many new areas of inquiry, for example, bringing time into the imaging process (time is manipulated and essentially ‘brought into coincidence’ at this plane).. I have previously noted that the eye may not be the ‘passive’ receiver that has been historically assumed but rather, part of an active (based on antenna behavior) system interrogating external reality (acting as a ‘phase conjugate mirror’?).

Enough for now.



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