A Statement of Clarification

by Gerald Huth on May 27, 2005

3 Cone Spectra

The above figure represents the trichromatic spectra corresponding to the three “classes of cones” that, in the “standard or historical model” are thought to represent the response of cone receptors on the retinal surface. I have referenced this oft-quoted figure elsewhere on the web page asserting (the red “X”) that short wavelength sensitive (“S” or blue sensitive) cones do not exist. In fact, it is my claim that no such thing as “classes of cones” exist.

In this work I derive three peaks of light sensitivity on the retinal surface that, at first glance, seem similar to the above. These are presented as Figure 3 of the full paper linked to the web page. At first blush these three peaks might be confused with the above BUT THEY REPRESENT SOMETHING ENTIRELY DIFFERENT. This, in fact, goes to the essence of my hypothesis.

If one, for example, focuses on the mid-band peak in the above figure (that corresponds to green at ~550 nm).one imagines that wavelengths interacting on either sides of the peak correspond to “shades of green blending into a rainbow of mixed colors as red and blue are added“. This is the normal interpretation of a “spectrographic plot” as the above represents. One goes on then to imagine that the myriad of colors conjured up by this view corresponds to the colors that we see, i.e., that the retina is the direct analogue of color photographic film.

This is not, however, how I propose the retina functions.

The three light sensitive regions on the retina that I derive, using the historically measured distribution of cones and rods on the retinal surface (Osterberg, 1935), result from simply counting cone and rod receptor appositions at each retinal angle… and assuming that light interacts between receptors. The three “curves” then are totally different representing light sensitivity as a function of retinal angle (as measured from the fovea) and not as a function of wavelength as the above.

My central “mid-band” response curve (whose peak is now, importantly, geometrically defined at a specific retinal angle on the retinal surface to satisfy Edwin Land’s prediction) corresponds in it’s entirety to only one wavelength (or “the same shade of green”) at each point, What varies on either side of the peak of this curve on the retinal surface is a variation of the density of detection sites, Such a variation in density corresponds to different levels of brightness (or, using the term used by Land, “lightness”) of light detected at this color. THIS IS EXACTLY WHAT EDWIN LAND DEDUCED FROM MEASUREMENTS MADE EXTERNAL TO THE EYE!

The retina then detects, from the fovea to a retinal angle of approximately 20 degrees, the brightnesses of three narrow wavelengths (or colors). We term these three colors “primary”.

The function of the retina is then NOT to discriminate a wide variety of colors but rather to detect only three primary wavelengths (or colors) that are directed to it by the refractive properties of the eye… what has been erroneously termed chromatic abberration. This is the basis for the historically measured (and never explained) distribution of cones and rods on the retinal surface and the fundamental reason why they evolved in this way. THE NEVER EXPLAINED, STRANGE DISTRIBUTION OF CONES AND RODS ON THE RETINA IS IN CONSONANCE WITH, AND EXPLAINED BY, THE LIGHT REFRACTIVE PROPERTIES OF THE BODY OF THE EYE.

Beyond this, the eye performs three Fourier or optical transforms of the acquired data synthesizing the color image as discussed in the full paper.

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{ 5 comments… read them below or add one }

Joseph Carroll December 28, 2005 at 9:22 am

You say “The Curcio reference (3) is more curious and again does not at all support the referenced statement. This paper relates a much more intensive effort than pursued by Williams to seek the elusive “S”cone using a number of diverse approaches. But the concluding comment of the paper is most telling stating that “all of the evidence (for the “S”cone) must be viewed as ‘inferential only.” Again, the italics are mine but this is the exact term used in the paper. I really do not understand what this means but it is certainly not very positive about the existence of the s-cone!”

Having read this paper, I find the following statement in the INTRODUCTION: “Many of these methods are inferential, and cells are presumed to be blue cones by virtue of the similarity of their distribution to that suggested by visual psychophysics”. You have misquoted this paper. The Curcio paper was referring to indirect methods to identify S cones, and using this to motivate her use of a direct staining technique to the S-cone opsin. There is no “Concluding remark” that states that “all” of the evidence for blue cones “must” be viewed as inferential – as you claim.

This amplifies the unscholarly approach you have taken to build your hypothesis and is disappointing.

ghuth December 28, 2005 at 10:08 am

I perhaps should have used the term “conclusion of the paper” instead of “concluding comment” but I believe that your summation very succinctly makes the point that I was trying to make.
GCH

Joseph Carroll December 29, 2005 at 1:49 pm

But the very fact that she was referring to previous studies is the point. What do you make of the actual results from her study (not her comment about studies that came before hers)?

ghuth December 30, 2005 at 9:38 am

I will go back and reread the Curcio paper (you make no comments about the other reference?)

I sincerely wish that you would argue from the position that would indicate that you had read and hopefully had some understanding of my basic premise..I have tried to make the text as clear as possible (and welcome suggestions to further clarify). Further, I don’t consider this an “hypothesis” but rather an “explanation” making sense of the rather disparate results and irrational expositions of the vision process in texbooks (being used by students) For example, might you comment on George Wald’s finding of the “blue blindedness” of the fovea (where 99% of cone receptors reside) – coming from an unimpeachable experimentalist and Nobel winner! Do you have an overall view of how the eye perceives an image? Do you believe the “inverted arrow diagrams” – with the large arrow encomapssing almost the entire retina – that pervade vision texts…and give the notion that the retina is the image plane of the optics of the eye? How do you reconcile the assymtetric distribution of cones and rods on the retina with this view..which would imply some sort of uniform RGB triads, photographic film-like, comprising the retina? Have you ever been interested in the light refractive properties of the structures of the eye…that show, when the proper refractive index values etc.are entered in a computer simulation exactly the distribution of light falling on the retinal surface that the geometrical construction that I propose illustrates. Mid-band “green” is refracted to 7-8 degrees..the unique point where rod density is sufficient to completely surround cones! Have you noticed that “blue” sensitive cones seem exceedingly difficult to find in experimental efforts?…the penultimate example ibeing the sequence in the BBC documentary “Colouful Notions” where the signal that is supposed to correspond to the response of these cones is obviously just noise! I do not believe that anyone intentionally intends to mislead..it is just that if something is said over and over (and repeated in the literature) if you go looking for it any fragmentary result will justify your belief…etc. It is my strong assertion that this is the case regarding blue sensitive cones!

Again, I wish that you would argue these central points with me…….. and not attack my scholarship!

GCH

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