Rethinking the Process of Vision

I had mentioned in my Comment of 1/20/06 the concept based on the “quantal catch” hypothesis that the rate of photon capture in cone receptors forms the basis for discrimination between cone types. This concept was referenced and proposed as factual in both the Mollon and Nathans papers. Upon reflection, this concept contains a glimmer of truth. I have proposed that an even more generalized interaction between all types of receptors is based on the wave nature of light. In my view, light as a wave interacts “along the sides of receptor outer segments” imparting energy to (via an evanescent wave), and electrically polarizing, what must be considered fundamental, “devices” composed of two adjacent outer segments. I have diagrammed this in “Diagram of the Fundamental Light Detection Device of the Retina” under the heading “Important Material” on the webpage. One might view the overall effect, i.e., energy absorbed by the receptor outer segment, as similar in the two cases but, the wave interaction provides crucial additional information. A polarized (“giant dipole”) signal from adjacent receptors in the wave construction encodes the directionality of the impinging wave thus satisfying the requirement of the Fourier equation - it already having been geometrically demonstrated that the retina is actually the Fourier plane of the optics of the eye.

I note again that the fundamental devices that I propose are also “tuned” to three very narrow optical wavelength bands (forming the necessary trichromatic RGB centers). In engineering terms this represents a “high Q” antenna geometry for each device. These devices located on the retinal surface to interact with wavelengths directed to them by the light refractive properties of the eye.

There is therefore no need to consider “spectral tuning” of light detection centers with the array of such centers detecting via the spatial density of tuned centers the intensity (or brightness) of each wavelength.

GCH

Those interested in this concept of vision should perhaps read George Wald’s “On the Blue-Blindedness in the Normal Fovea“ (J. Opt. Soc.Am, Vol.57, No.11, November 1967). Revisiting it in the course of writing the past day’s comments I find that the retina that Wald describes corresponds to a large extent with my description and a great deal of his writing can be read in this context. I had previously noted that the retina described in Wald’s Nobel Lecture (I believe it was his Figure 15) appears very much as the geometric retina that I define.

But first, two remarks. (1.) In the context of identifying the color detection centers and morphology of the retina, Wald maddeningly says nothing of the, what has to be related, optical physics of the image formation process used by the eye. It seems just assumed (again, I guess!) that the retina forms the image plane of the “camera” that is the eye. After describing a retina much as I see it, namely, that color detection centers are spatially separated on the retinal surface in areas (rings) around the fovea, Wald just leaves it at that not relating this morphology to any concept as to how an image is formed! (2.) Wald in his discussion uses the only light detection model available to him at the time, namely, that the trichromicity of the vision process must be equated to “three types of color sensitive cones”. He does, however, introduce the term “blue receptor function” (p.1294, italics mine) in the place of “blue sensitive cone”.

At the risk of being accused of taking Wald’s thoughts out of context I will transcribe some sections of his text. I truly believe that these sections mirror and summarize the thrust of the paper.

p.1289..from the Abstract:

“The blue cone system falls in sensitivity from the border of the photopic zone – the functionally all-cone areas – to a minimum, usually to extinction, at it’s center”…”Also the red – and green cone systems display the opposite gradient; their sensitivities decline regularly from the center toward the borders of the fovea and beyond”

This describes the morphology that I define with even more geometric precision..This is undoubtedly the basis for the retinal sensitivity curve that Wald presented in his Nobel lecture. It is truly beyond me how anyone seeing this – color sensitivity segregated into specific areas or “rings” on the retinal surface did not think to relate this diffractive surface to the wavelength refractive properties of the eye!

p.1290:..I have been anticipated!

Wald, (after calling it a misconception), quotes: “Wilmer had thought to explain color vision in terms of only two kinds of cone, or cones, and cone-like rods, the third color mechanism, that for blue, involving the cooperation of ordinary rods (ref).. Hence, he too expected to find no blue receptors throughout the entire photopic area…”

Wald defines the “photopic area” as the region of the retina “dominated by cone vision” and generally subtending an angle of 1-1.5 degrees. He goes on to say “that the photopic area of the retina contains large numbers of such blue-sensitive cones”. I believe, in the context of my comment yesterday, that he is mistaken in ascribing this function to cones – it is in this critical area of the retina that rods are beginning to intrude on the cone matrix and…the logic of my thoughts yesterday.

(ref): E.N.Wilmer, Nature 153, 774 (1944), and E.N. Wilmer, J. Theoret. Biol., 1, 141 (1962))

p.1294:

“It seems therefore that the absence or near-absence of blue receptor function is characteristic only of the center of the fovea. It is a matter, not primarily of size of field, but of foveal topography”

p.1296:

“The general gradient of cone concentration in the fovea therefore runs counter to the gradient of blue-cone sensitivity. At the center of the fovea, where con3es are most dense, blue-cone sensitivity is minimal, and blue-cones are usually entirely absent. Conversely, at the borders of the photopic area, where the blue-cone sensitivity is highest, the total number of cones has decreased markedly. This opposed distribution is reflected in a converse pattern of relationships that involve the red and green cones”

p.1298:

“…whereas the sensitivities of the red and green-mechanisms are highest at the center of the fovea, and decline regularly with distance from it, the blue cones show just the opposite gradient of sensitivity, rising from a minimum at the center of the fovea to one half degree to one degree out…”

p.1298:

“Congenital blue-blindedness is such a rarity that its existence was doubted….the most optimistic estimate of the incidence of congenital blue-blindedness is 1 in 13,000…”

On p.1299 Wald recognized the problem of chromatic aberration in the eye:

“Any lens made of one material exhibits chromatic aberration; it refracts short wavelength light more strongly than long wavelength light, and hence brings blue light to a shorter focus than red. Color-corrected lenses can of course be made by using two glasses differing in refractive index; but, so far as is known, no animal has yet succeeded in developing a color-corrected lens. Though the cheapest of cameras have color-corrected lenses, the lens system of the human eye – as Newton observed – has no color correction whatever”

p.1300:

What we take, therefore, to be normal, trichromic vision is the particular property of an annular zone of the central retina, lying between the blue-blind fixation area and a red-green blind zone some 20-30 degrees out. The special importance of this central zone is that we depend upon it almost exclusively for all phase of photopic vision, and that, all testing of color vison is confined within it, rarely extending mor ethan 2 degrees beyond the fixation point”

GCH

I had discussed this paper previously but recently have had a chance to revisit it at the prodding of my son. If the idea that a “mosaic of three types of cones” forms the foveal region of the retina were true then my concept of light interaction with the retina would have no merit. BUT, IN A CURIOUS WAY INDEED, I BELIEVE THAT THE RESULTS PRESENTED IN THIS PAPER BESIDES REPRESENTING A FACTUAL DESCRIPTION OF LIGHT INTERACTION WITH THE FOVEA SIMULTANEOUSLY AND EXACTLY SUPPORT MY CONCEPT! I will explain and suggest an extension of the RW experiment that might be done to clear this issue.

Parenthetically, the authors seem to assume that the retina forms the image plane of the optical system of the eye..and therefore that its light detection elements must form some sort of analogue of color photographic film or the pixel array of a silicon imaging device. I will discuss this in greater detail later but this view (in my opinion a wrongful view!) permeates the literature of vision science and forms the basis for the results presented in this paper (I demonstrate that the retina forms a diffractometric Fourier transform plane and not an intensity-only sensitive image plane of the eye),

The assumptions of the Roorda Williams letter to Nature:

1.) RW undertake heroic measures to optically visualize individual color detection sites of the retina – that they assume are solely cones. Note that such entities, whatever they are, are small indeed on the retinal surface having dimensions approaching the wavelength of visible light – and thus, the limits of light microscopy. RW employ multiple measurements and complex image registration methods to finally define the final precise imagery. This results in some “blur” admitted by the authors. The question is how much blur? And what is the spatial resolution of the final images? The light detection elements certainly appear as large single diameter cones……but are they?

2.) The methodology of the paper uses wavelength selective bleaching to render the different light detection sites visible. Bleaching is nature’s way of preventing overload and resultant damage to the light detection centers of the retina. It involves in my view a reorientation of the retinal chromophores (whose role I discussed in a recent comment) away from the direction of incident light (this direction, in accord with the measured dichroic orientation of these chromophores, is transverse to the direction of incident light). This method of visualizing individual light detection sites, however, seems appropriate.

3.) It is stated that the images are of the cone mosaic as it appears at one degree of retinal angle (i.e., the parafoveal region). If this is accurate, at this angle, according to George Wald (J. Opt. Soc. Am , Vol.57, No.11, November 1967), quoting Osterberg’s data in his Figure 9 on p.1295, indicates that at one degree cone and rod densities are nearly equal. Precisely, cone density is ~45,000 / mm2 and rod density is ~35,000 / mm2. This is the region of the retina where rods are starting to intrude upon the orderly hexagonal array of cones. One begins to find an increasing number of isolated cone-rod appositions (and even more isolated rod-rod appositions to be discussed below). One degree of retinal angle is a crucial region as cone and rod densities are falling and rising precipitously at this angle. Rod density continues to increase until at 7-8 degrees there are sufficient rods to completely surround each cone (which they do) and define the geometric midband sensitivity point of the retina.

So what are the wavelength detection centers that Roorda and Williams visualize? I would guess that the spatial resolution that they are able to obtain is not sufficient to visualize rod-cone appositions, or, alternatively, blurs them to the extent that they appear similar in size to the “red” interaction sites. The authors make a point about the randomness of the green sites and this is exactly as it should be at this retinal angle following the logic that I pursue.

And what of the infamous blue detection sites shown in Figure 3, that I claim do not correspond at all to “blue sensitive cones”? I would propose that these actually are blue detection sites ….but.. that these sites arise from the few rod-rod appositions that appear as rods continue to crowd into the cone array. The low density of these sites is in exact consonance with this logic. Additionaly is support of this argument, blue sites are found adjacent to, or associated with (except for two outlyers), the green sensitive centers. These would be associated with the few statistically present rod-rod appositions.

I must add that Curcio (“Human Receptor Topography”, Journal of Comparative Neurology, 292:497-523, 1990) seems to disagree with Wald/Osterberg stating in the Abstract “In the fovea, the average horizontal diameter of the rod-free zone is 0.350 mm (1.25 degrees)”. This number seems to have been arrived at using the method described on p.503 of the paper titled “Conversion to Visual Degrees” which is more complex than I choose to manage..so I will leave this point for others to sort out.

Just another thought in regard to the Curcio paper..I have been taken to task for “not understanding” data from this paper wherein it is reported that the size of cones is not constant but rather varies between individuals. I would certainly believe that this is so..genetically mediated. I have proposed rather clearly that the effect of varying the size of cones would be..making the crucial assumption that the refractive properties of the eye are not changed … to offset the geometrically determined midband point (7-8 degrees). Assuming that midband 550 nm wavelengths arrive at the same location, any slight offset would lead to color variant vision or “color blindness” (see Land’s work), Also, the long wavlength limit of the visual response would be extended for individuals having larger cone receptors. Is this measurable?

IN SUMMARY..I WOULD MAKE A PREDICTION AND A REQUEST. IF THE ROORDA GROUP WOULD EXTEND THIS TYPE OF MEASUREMENT TO LARGER RETINAL ANGLES I BELIEVE THAT THEY WOULD FIND THAT THE DENSITY OF GREEN SENSITIVE CENTERS WOULD CONTINUALLY INCREASE UNTIL AT SEVEN TO EIGHT DEGREES REPONSE WOULD BE TOTALLY GREEN. IMAGE RESOLUTION COULD BE RELAXED A BIT AS I BELIEVE THAT IT WOULD BECOME QUICKLY APPARENT THAT THE BEHAVIOR THAT I PREDICT WOULD BE PRESENT. I WISH THAT THIS MEASUREMENT COULD BE UNDERTAKEN.

GCH

I have proposed that green (midband or M) sensitivity of the retina derives from the optical antenna dimensionalities formed by the appositions of cones to rods. Moreover, such centers actually geometrically define the exact midband sensitive point on the retinal surface.Vision literature portrays midband sensitivity as being derived from the response of “green sensitive cones”..distributed somehow in the foveal area of the retina

The region that I define as M sensitive begins at retinal angles of 1-2 degrees where the first rods appear in the otherwise all-cone fovea (Osterberg states that the first rods appear at 0.13 mm from the foveal center). The M sensitive region then peaks at retinal angles of 7-8 degrees (the fixed midband point where rod density is first sufficient so that eight rods completely surround each cone) yielding to short wavelength (or “S” sensitive) response at angles of ~ 12 degrees (where rod receptors become dominant). This behavior is shown in Figure 3 of my original paper.

Thus I would claim that the M and L (long wavelength) sensitive areas of the retina are distinct and spatially separated with the M region forming a circular ring around the central, all-cone L region. Further, the retina from the all-cone sensitive fovea to the peak of midband M sensitivity lies within angles of less than 8 degrees – BUT THE TWO REGIONS ARE SPATIALLY DISTINCT AND DO NOT AT ALL RESEMBLE UNIFORMLY PIXILATED PHOTOGRAPHIC COLOR FILM.

It may be important that the two regions have different areas with the M region being larger than, and forming a “ring around”, the central L region. These different areas must be calculated andmay bear on “quantal catch” (or, more appropriately, “quantum efficiency”) considerations discussed elsewhere.

Now…it seems that both psychophysical and microspectrophotometric (MSP) measurements agree that response of the M and L regions overlap to a large degree. See the response curves referenced yesterday (but one can find them in any vision text). Specifically, the transient chromatic adaptation (psychophysical) type of measurement of cone sensitivity referenced in Stockman et al (J. Opt. Soc. Am. A, Vol.10, No.12, December 1993) seems to indicate that this type of transient chromatic adaptation measurement is made using lights focused to a central (foveal?) two degrees with a surround encompassing eight degrees of retinal angle. (I am no expert on this type of measurement and stand to be corrected if I am wrong), Assuming this, both the L and M regions that I define would be simultaneously interrogated in this measurement. Two separate regions could possibly be defined (and apparently are) in color comparison measurements as it is generally in this region that wavelength comparison is effected (with the fixed midband point at 8 degrees).

I would propose this as the reason for the overlap in the M and L response curves. It would be natural to assume, as has historically been done, that the M response derives from a “different type of cone” but I do not believe that this is the case.

Which leaves the second (MSP) type of measurement to be dealt with. It is purported that MSP defines separate M and L cone types. Stockman et al, as I noted yesterday, discuss the problems with MSP to which I add physics considerations (diffraction at distances approximating the wavelength of light is a very powerful effect indeed!). In reviewing this lengthy paper one has a difficult time from their Figures 11, 12, and 13 discerning any spectral differences at all in M and L cone response. The only differences seem to be in “quantal sensitivity”. Even after the data referenced are adjusted and corrected in innumerable ways (so stated) the spectral responses appear strikingly the same! Even the measurements made on humans and rhesus monkeys do not appear to differ. I really believe that from my (physics) point of view, this should be so. This, however, is a very difficult point for me with my limited knowledge of this type of measurement to assess…and I stand to be educated.

GCH

I have written about this before but in conjunction with my recurring use of the term “nanowire” this reference may bear repeating. A paper in Nature (http://www.news.harvard.edu/gazette/2004/01.08/09-nanoeye.html) authored by a Harvard University group led by Mazur and Tong has recently found that when a fiberoptic lightguide is reduced in diameter to dimensions less than light wavelength (i.e., less than ~0.5 micron of 500 nm), instead of being transmitted through the interior of the guide, light flows around (or on the “outside of”) the guide itself. They further find that the more the diameter of the guide is reduced the more light flows outside of the guide.

The diameter of retinal receptors approximates (or is even less than) the wavelength of visible light. The historic and extensive research in the vision science field that modeled retinal receptors as lightguides, i.e., considering that light flowed internally within the guide, did not anticipate this behavior.

It is my belief that this new result exactly validates my hypothesis..i.e., that light interaction is between and not “within” retinal receptors! Further, the linkage between the evanescent wave nature of this light corresponding to the transverse dichroic orientation of retinal pigment further substantiates my claim.

I add a quote from the Mazur/Tong paper: “The nanowires carry light via evanescent waves that envelop the slender filaments. If two of the wires touch, light can jump directly from one to the other, something that’s not possible with conventional fiber optics.”

GCH

I have proposed that it is the nanostructure of the cone and rod organization of the retina that controls light interaction with this surface. In this new view the eye evolved to detect incoming light as the wave of classical physics in inter-receptor spaces while the cones and rods themselves perform the function of “quantum confined electron sites” or, as generic “nanowires”. This is at odds with the long held “purely quantum” view that “light photons interact with pigment molecules contained within receptors”. I must note that my view in no way conflicts with quantum reality….one must simply replace the idea that “a photon interacts” with the more general “a quantized interaction occurs”. I have been informed by elements of the vision science community (in no uncertain terms!) that my view cannot be correct in light of the historically held pigment mental construction.

In my initial paper I had proposed thinking of the receptors themselves as entities emphasizing the nanostructural overview (the simple geometric logic of that overview is still the overriding factor in light detection!). I viewed the retinal/opsin pigment complexes contained within the thylakoid disks of receptors as energy-accepting sites with the chromophoric retinal molecule performing that (among other) function with the various opsin configurations providing the structural framework for spatially defining (or orienting) the position of the pigment complex within the bilipid membrane of the thylakoid disk.

Upon reflection, and jogged by criticism that I was disregarding the pigment model, it became clear that the structure of the pigments should differ to accommodate the three different receptor dimensional arrangements (i.e., the C-C, C-R, and R-R appositions). These three appositional dimensionalities define the three light absorption peaks of my proposal and thus three quantitatively different energy situations (I suppose in “optical antenna” terms a “resonance” might be assumed). This would explain the differing energy of pigments that has been historically found.

To the subject of pigments themselves……I began by reviewing a paper by Mollon (Proc. Natl. Acad. Sci. USA, Vol. 96, pp4743-4745, April 1999). The author presents (his Fig.1, p 4743) the same photopigment response curves published over and over elsewhere (and which I have critiqued in my section “I Do Not Believe That Classes of Cones Exist”), I have noted that the curves, based on microspectrophotometric (MSP) type of measurement (see below), have strange characteristics. First, they are normalized to the same sensitivity levels when I claim that there is not evidence for doing this ..or positioning the blue (or “S”) response at this level (or indeed, at any level -but that is another story). The green and red photopigment response curves labeled here as “M” (or midband) and “L” (or long wave) overlap and are exceedingly closely spaced with the red curve showing vanishing sensitivity at the red wavelengths (650-700 nm) to which it is supposed to be responsive. Mollon does include a color bar in the figure that is helpful..showing that the L curve peaks in the yellow/green region of the spectrum. Interestingly, the M and L peaks sit almost exactly astride the 550 nm midband point of the visible spectrum ..more about this below.

Nathans (Neuron, Vol.24, 299-312, October 1999) quantitiates the above M and L curves to ~530 and ~560 nm. He also makes a statement (p. 302) that I will quote directly “Why do humans and other trichromatic primates have cone pigments with absorption maxima at ~425, ~530, and ~560 nm rather than at some other set of wavelengths? In particular, why are the absorption spectra of the green and red (I note – not “M” and “L”) pigments so close together relative to the blue pigment spectrum?” I must note that he goes on to provide answers to these questions that I will discuss below.

Now…further on in Nathans, in his explanation of the above, on p 303, he presents psychophysically derived(important!) pigment absorption spectra. These absorption curves - as opposed to the MSP derived curves noted above - seem to solve the red sensitivity issue that I raised with both the M and L curves displaying finite sensitivity in the 650-700 nm region (they are still, however, normalized to the same sensitivity levels that I do not understand)…but they do, importantly, display red response!!!!

Stockman et al (J. Opt. Soc. Am. A, Vol.10, No.12, Dec. 1993) discusses the differences between psychophysically-derived and microspectrophotometrically-derived (MSP) types of photopigment measurement. The authors take issue with the MSP measurement for some of the same reasons that I had noted…that they are made transversely whereas the traditional photon/pigment interaction model supposes as axial incidence (even Stockman, however, does not mention the transverse dichroic orientation of the photopigment chromophore that supports my view..and has never seemingly been explained). I would propose, among other issues, that the MSP measurement that is made with the receptor removed from its natural (nanostructural!) milieu within the retina,i.e., “laying it on it’s side in a bath of fluid whose index of refraction differs….etc.” (such a measurement can be considered as “interrogating a gradient of refractive indices across the receptor”). The psychophysical measurement, on the other hand, interrogates the photopigment in its natural, nanostructurally controlled environment…and thus, elicits a truer result.
HEREIN I BELIEVE LIES THE ANSWER WITH THE DIFFERENCE IN THE TWO TYPES OF MEASUREMENT SUPPORTING MY ASSERTION THAT THE IN-VIVO (ACTUALLY “LIVING”) NANOSTRUCTURE OF THE RETINA CONTROLS LIGHT ABSORPTION. THE MSP TYPE OF MEASUREMENT MERELY QUANTIFIES DIFFERENCES OF PHOTOPIGMENT RESPONSE .. REFLECTING ENERGY LOSSES THAT WILL PROBABLY BE FOUND TO CORRELLATE WITH THE STRUCTRURE OF THE RETINAL/OPSIN COMPLEXES.

Back to the Nathans paper(p.303) and his method for calculating spectral discrimination curves from visual pigment absorption spectra. I point specifically to his Figure 5 A and B. He uses a rather complicated “amplitude of differencing” method that he further refers to as “line element analysis”…”first introduced by Helmholtz with subsequent refinements by Schrodinger…”.and who am I to quarrel with those distinguished gentlemen! (I am reminded here of an anti-Land letter that I received pointing to a reference “Land! Land! where the author began by excoriating Land “who was he to dispute Helmholtz! ..which Land did not do!).

The method described by Nathans (and repeated in Mollon) posits the photon-interacting-with-pigment hypothesis and uses the “quantum catch” notion that it is the number of photons “caught” by a receptor that leads ultimately to the logic of spectral discrimination. A statement is made that I believe should give anyone pause..that the photon “loses its identity” (i.e., any information about any wavelength association) upon the process of absorption . This would make me nervous in placing belief in any hypothesis using this assumption..somewhat like the conundrum in quantum physics of the “collapse of the wave function”.

In any event, Nathans in Figure 5B, using the above method, derives three retinal response peaks that are reminiscent of the three peaks that I derive using (I believe!) exquisite geometrical simplicity (Figure 3 of my original paper). A distinct midband peak at 550 nm is calculated by Nathans which is where it should be. I locate this peak with simple geometric logic aand, moreover, can define it as a precise “fixed reference point on the retinal surface.

In this rudimentary exercise of reviewing pigment literature one is left with a few distinct impressions.

First, that the M and L responses (Nathans Figure 5 A-H) control spectral discrimination with much less concern with, the blue or “S” cone specie. In the analysis following from this figure the blue peak is “just there” normalized to it’s improper level (my view) while the positions of the M and L peaks control things.

Which brings me to the point, it seems to me that this entire “quantum catch”- based method of calculating spectral discrimination is based on normalized peak levels…which seem arbitrary to me……how can this be?

On blue cones from Nathans (p.304), “”The primate retina has solved both of these problems (discussed above) by sprinkling the retina only sparingly with blue cones, and, in some species, decreasing their representation in the central fovea (references)”.

The point that the M and L curves (and noting that they are labeled as such) straddling the 550 nm mid-band point seems to echo Land’s theory that “color” is determined by the eye obtaining a ratio of signals (“brightnesses”) on either side of mid-band. The above goes into how such a ratio of signals might be affected by retinal circuitry. I have not concerned myself with this limiting my attention to the physics of light interaction with the retina itself..

Although this may be somewhat disjointed I am going to post it anyway as this is all the time I have

GCH

The accepted view of the physics of light interaction within the eye is that photons interact with different pigment molecules contained within the cone and rod receptors of the retina and that this forms the basis for trichromatic vision, and, in effect, explains everything. I have proposed an alternative mechanism for this light interaction that seems at first glance to be at variance with this photon/pigment hypothesis. Specifically, I propose that the overall geometric nanostructure of retinal organization, that when viewed from our emerging knowledge of “optical antenna structures”, explains at once the trichromicity of vision and provides a logical explanation as to how the visual image is acquired – in the Fourier domain. Other vision results are explained including the evolution of the specific organization of retinal receptors, George Wald’s finding of the “blue blind” fovea, and, the color vision experiments and theory of Edwin Land. Although the concept posits that light interacts on the retina as a classical wave, the quantum nature of the interaction is preserved in concluding that the absorbing mass- the electron - is contained within the quantum confinement dimension.

I am continually being challenged to the point that “the photon/pigment hypothesis explains everything…….so how can you be correct?”. I will provide a short answer here with longer more detailed arguments presented shortly.

I am reviewing a number of papers suggested to me focusing on the identification, and even genetic manipulation, of these retinal pigments. My comments here focus on thoughts gleaned from a review paper by Nathen that pretty well summarizes the pigment view: (“The Evolution and Physiology of Human Color Vision: Insights from Molecular Genetic Studies of Visual Pigments”, Neuron, Vol.24, 299-312, October 1999).

In summary: I proposed in the body of this work that the retina should actually be considered, in overview, as an “array of structural receptor/”nanowires” with three different interreceptor spacings that result from an admixture of two different receptor sizes – the cones and rods”. I went only as far as proposing that these nanowires were generic, i.e., energy absorbing pigments in both cone and rod receptors possessing the same energy absorption character. In retrospect this should not be the case. Energy absorbing pigments (i.e., retinal plus an opsin component) contained within the bilipid membrane of the thylakoid disks of each type of receptor would undoubtedly have different structural configurations required by the differing dimensional spacings of the cone-cone, cone-rod, and rod-rod appositions. I would think therefore that the small differences (always strangely only a few nanometers centered around mid-band)) that have been observed in the response of retinal pigments represents a structural response to these spatially determined, energy absorption requirements. The measured responses of these retinal pigment molecules are obviously very real but they do not represent the fundamental light absorbing mechanism of the retina.

TO BE CONTINUED

GCH

The thought keeps recurring that the science of vision has done itself a great disservice by conjuring up the idea that single cone receptors of the retina detect “color” as if they were some sort of completely self-contained laboratory spectrometer. This type of lazy mental construction has led, for example, to the introduction of such pseudo-scientific concepts as “intelligent design”. The actual situation is far simpler and fundamental. It is the appositional distance between two cones that detects the narrow wavelength directed to that specific area of the retina (i.e., the all-cone fovea) by the evolved, light refractive properties of the structure of the eye! For the case of cone-to-cone appositions, this wavelength, in addition to defining the actual long wave limit of the visual response, forms the “primary red” that leads (in conjunction with the other two geometric mid-band and short wavelength limit brightness peaks) to a synthesis of the many hues of “color” presented to the appropriate centers of the brain. I note that Edwin Land deduced this from measurements made external to the eye!
GCH

Using the optical antenna construction that is the basis for this work it is seen that the retina is sensitive to only three wavelengths: a.) the actual long wavelength limit of visual response (i.e., red) defined by cone-cone appositional distance in the fovea, b.) a geometrical, exact mid-band wavelength (i.e., green) defined by cone-rod appositions at 7-8 degrees of retinal angle, and c.) the actual short wavelength limit (i.e., blue) of visual response defined by rod-rod appositional distance. We define these three wavelengths as the “primary wavelengths”usually designated as “RGB”. Most importantly, through variation of antenna density, the three peaks thus formed are sensitive to levels of BRIGHTNESS for each wavelength and not to variablity of wavelength as is usually assumed. Taken together these retinal characteristics validate the theory of color vision of Edwin Land that must be studied to understand the significance of this retinal construction. For example, full color (as opposed to the three”primary RGB wavelengths) is synthesized by the eye obtaining a ratio of brightnesses on either side of the geometric mid-band point exactly as Land predicted.

I have attempted to show that this retinal construction and the new view of vision that follows explains so much that has been left unexplained in vision science. Wald’s experimental finding of a “blue blind” all-cone fova is one example…and I have pointed out many more examples in the text of the paper.

I would like (but will probably not see!) anyone criticizing the work to argue from the above fundamental construction and the extensive agreement with the characterisitcs of the vision process that I claim follow from it. It is not constructuve to argue that becuase I (apparently) did not read this or that paper the entire premise is invalid!

GCH