I have come upon a website from David William’s Lab dated February 2009 entitled “THE TRICHROMATIC CONE MOSAIC” that essentially rehashes the 1999 Letter to Nature by Roorda and Williams that I have previously written about (see more below).
One sentence from the opening paragraph of this paper:
“For hundreds of years, scientists, such as Thomas Young (1801) have proposed that the retina contains three different types of cones (emphasis mine) whose signals are combined to provide us with normal color vision”.
The Wikipedia entry for Thomas Young states that:
“In 1801 ………in his Lectures he presented the hypothesis, afterwards developed by Hermann von Helmholtz, that colour perception depends on the presence in the retina of three kinds of nerve fibres (again, emphasis mine) which respond respectively to red, green and violet light.
The entry goes on to say the obvious:
“This foreshadowed the modern understanding of color vision, in particular the finding that the eye does indeed have three color receptors which are sensitive to different wavelength ranges”.
“Receptors”….where? how?
I submit that these three types of “fibres” might just as easily have included “rods” or even (god help us!) “the three geometric nanostructural appositions between cones and rods”. Who made the determination that these were solely the “cones? ” They might easily be construed more generally as “light detection sites”. I believe that Young’s essential contribution in all of this was really identifying the trichromicity of vision.
I have returned on numerous occasions to discussion of a Letter to Nature by Roorda and Williams “The Arrangement of the Three Cone Classes in the Living Retina” (Nature, Vol. 397, 11 February 1999, pp520-522). Accepting that this group had developed methods for: 1) spatially imaging and , 2) identifying the wavelength response, of retinal receptors, I asserted that they were not “S, M or L cones” but rather the three appositional center-to-center distances between both rod and cone receptors that is the central point of my explanation for the interaction of light with the retina. I noted that their measurements were made at a retinal angle near one degree (or at the edge of the fovea). This is a point on the retina where the density of cones and rods is rapidly changing with cone density falling and rods being introduced statistically into the admixture. Although this is shown in the classic Osterberg figure of retinal morphology, a clearer picture of receptor densities can be seen in a figure from George Wald’s “Blue-Blindedness in the Normal Fovea” ( JOSA 57, No.11, November 1967):
I have inserted a red line at one degree to indicate where the RW measurements were made. It is evident that rods are present in large numbers at this angle (~35,000/sq mm versus a cone density of ~45,000 / sq mm. Where are the rods in the RW figures? There is probably some explanation for this – and I would like to hear it. I would propose that the purported response of “L” or red wavelength cones is not the response of a single cone but actually a light detecting center that corresponds to cone-to-cone appositions. It is these appositions that predominate at this angle – and do so in RW’s figures.
Correspondingly, the “M” or green cones do not correspond to single cone response but rather to light detection centers formed by cone-to-rod appositions. This is certainly consistent with the large number of rods (almost equaling cone density) known to be present in this region.
The authors talk of the sparse “S” cones (referring to the “blue” or short wavelength sensitive variety). Again, I propose that these light detection centers correspond to the statistically (VERY) few rod-to-rod appositions that appear in this region. PLEASE – refer to the drawings of retinal topography in this region on pp30-31 of Pirenne (VISION AND THE EYE,. Chapman and Hall Ltd.) and note that this is exactly the case!
(I am going to note parenthetically here that the two “endpoint” receptor appostions (cone-cone and rod-rod) actually define the precise wavelength limits of the visual band. An exact, geometrically-defined midband wavelength is defined by the cone-rod appositional distance. The presence of this fixed midband point is crucial in explaining the color constancy of vision and the mechanism for determining the hues that we term “color” proposed by Edwin Land…….and more! )
R&W seem continually to be attempting to find deviations from randomness in these three “classes” of cones. I imagine that this follows from attempting to visualize the eye and retina as a “camera/photographic film” analogue that pervades the entire literature of vision. In this attempt they seem not to (nor should they) succeed. The historic measurements of Osterberg show definitively that retinal receptors are statistically distributed.
But…there IS order in the distribution of receptors. The primary order of course are the three circularly symmetric rings of single wavelength response (the trichromicicty of vision) that surround the fovea – and that is the basic finding of this work. The second is the octagonal symmetry of eight rods around each cone at 7-8 degrees of retinal angle shown in the following:
This figure is taken again from Pirenne, VISION AND TH EYE, Plate 6 titled “Close to the Yellow Spot”. A precise spatial order?
(I must note here again that the only ratio of dimensions that can lead to an octagonal symmetry is 1.8:1 – and that this ratio correspnds to the visual band – 700-400 nm .)
I submit that the RW measurements precisely support my explanation.
After reviewing the Nature paper, I proposed that, again accepting the validity of the RW receptor imaging techniques, that the authors make similar measurements at larger retinal angles on the retina surface – in the region of 7-8 degrees. I have indicated this angle by inserting the green line on the above figure.
This region is perhaps the most critical on the retina as at this point there are sufficient number of rods to completely surround each of the diminishing number of cones. Retinal morphology at this point consists completely of eight rods around each cone octagonal “rosettes”. RW might note that this is a point of complete spatial order! I have pointed out on too many occasions that the only ratio of the sizes of cones to rods that can result in this geometry is 1.8:1 and that this corresponds to the visual band (700-400 nm).
I predicted that such measurements would show a preponderance of “green light detection centers”. It is at this angle that the density of rods is sufficient to completely surround each remaining cone and therefore response should be entirely green! Such measurements were made and reported in a paper (3832/A375) presented at the ARVO 2008 Annual Meeting titled “Arrangement of the Human Trichromatic Cone Mosaic in Peripheral Retina” and authored by O. Masuda, H. Hofer, J. Carroll and D.R.Williams. This work seemed to respond to my request extending the previous RW. work to larger retinal eccentricities. Results showed essentially what I had predicted in, what the authors termed, a “green cone clumping” effect at this angle. This “clumping” was noted as the first hint of a spatial order (of “cones”) on the retina.
To summarize, the light detection centers imaged by the authors do not correspond to a response of “cones” but rather the distances between receptors as the body of this work posits. There IS a spatial order to light detection center response on the retina and it corresponds to the three precise, circularly symmetric, single wavelength detection regions as explained in this work.
Seeing this finally makes clear the many historically unexplained conundrums of vision –a fundamental explanation for the formation of the visual image (in the Fourier domain), the never explained color constancy of vision, and, not unimportantly, the basis for color vision .
What more can I say!
GCH
Ojai,CA
3.24.10
REVISITING “THE TRICHROMATIC CONE MOSAIC”… YET AGAIN !
by Gerald Huth on March 24, 2010
I have come upon a website from David William’s Lab dated February 2009 entitled “THE TRICHROMATIC CONE MOSAIC” that essentially rehashes the 1999 Letter to Nature by Roorda and Williams that I have previously written about (see more below).
One sentence from the opening paragraph of this paper:
“For hundreds of years, scientists, such as Thomas Young (1801) have proposed that the retina contains three different types of cones (emphasis mine) whose signals are combined to provide us with normal color vision”.
The Wikipedia entry for Thomas Young states that:
“In 1801 ………in his Lectures he presented the hypothesis, afterwards developed by Hermann von Helmholtz, that colour perception depends on the presence in the retina of three kinds of nerve fibres (again, emphasis mine) which respond respectively to red, green and violet light.
The entry goes on to say the obvious:
“This foreshadowed the modern understanding of color vision, in particular the finding that the eye does indeed have three color receptors which are sensitive to different wavelength ranges”.
“Receptors”….where? how?
I submit that these three types of “fibres” might just as easily have included “rods” or even (god help us!) “the three geometric nanostructural appositions between cones and rods”. Who made the determination that these were solely the “cones? ” They might easily be construed more generally as “light detection sites”. I believe that Young’s essential contribution in all of this was really identifying the trichromicity of vision.
I have returned on numerous occasions to discussion of a Letter to Nature by Roorda and Williams “The Arrangement of the Three Cone Classes in the Living Retina” (Nature, Vol. 397, 11 February 1999, pp520-522). Accepting that this group had developed methods for: 1) spatially imaging and , 2) identifying the wavelength response, of retinal receptors, I asserted that they were not “S, M or L cones” but rather the three appositional center-to-center distances between both rod and cone receptors that is the central point of my explanation for the interaction of light with the retina. I noted that their measurements were made at a retinal angle near one degree (or at the edge of the fovea). This is a point on the retina where the density of cones and rods is rapidly changing with cone density falling and rods being introduced statistically into the admixture. Although this is shown in the classic Osterberg figure of retinal morphology, a clearer picture of receptor densities can be seen in a figure from George Wald’s “Blue-Blindedness in the Normal Fovea” ( JOSA 57, No.11, November 1967):
I have inserted a red line at one degree to indicate where the RW measurements were made. It is evident that rods are present in large numbers at this angle (~35,000/sq mm versus a cone density of ~45,000 / sq mm. Where are the rods in the RW figures? There is probably some explanation for this – and I would like to hear it. I would propose that the purported response of “L” or red wavelength cones is not the response of a single cone but actually a light detecting center that corresponds to cone-to-cone appositions. It is these appositions that predominate at this angle – and do so in RW’s figures.
Correspondingly, the “M” or green cones do not correspond to single cone response but rather to light detection centers formed by cone-to-rod appositions. This is certainly consistent with the large number of rods (almost equaling cone density) known to be present in this region.
The authors talk of the sparse “S” cones (referring to the “blue” or short wavelength sensitive variety). Again, I propose that these light detection centers correspond to the statistically (VERY) few rod-to-rod appositions that appear in this region. PLEASE – refer to the drawings of retinal topography in this region on pp30-31 of Pirenne (VISION AND THE EYE,. Chapman and Hall Ltd.) and note that this is exactly the case!
(I am going to note parenthetically here that the two “endpoint” receptor appostions (cone-cone and rod-rod) actually define the precise wavelength limits of the visual band. An exact, geometrically-defined midband wavelength is defined by the cone-rod appositional distance. The presence of this fixed midband point is crucial in explaining the color constancy of vision and the mechanism for determining the hues that we term “color” proposed by Edwin Land…….and more! )
R&W seem continually to be attempting to find deviations from randomness in these three “classes” of cones. I imagine that this follows from attempting to visualize the eye and retina as a “camera/photographic film” analogue that pervades the entire literature of vision. In this attempt they seem not to (nor should they) succeed. The historic measurements of Osterberg show definitively that retinal receptors are statistically distributed.
But…there IS order in the distribution of receptors. The primary order of course are the three circularly symmetric rings of single wavelength response (the trichromicicty of vision) that surround the fovea – and that is the basic finding of this work. The second is the octagonal symmetry of eight rods around each cone at 7-8 degrees of retinal angle shown in the following:
This figure is taken again from Pirenne, VISION AND TH EYE, Plate 6 titled “Close to the Yellow Spot”. A precise spatial order?
(I must note here again that the only ratio of dimensions that can lead to an octagonal symmetry is 1.8:1 – and that this ratio correspnds to the visual band – 700-400 nm .)
I submit that the RW measurements precisely support my explanation.
After reviewing the Nature paper, I proposed that, again accepting the validity of the RW receptor imaging techniques, that the authors make similar measurements at larger retinal angles on the retina surface – in the region of 7-8 degrees. I have indicated this angle by inserting the green line on the above figure.
This region is perhaps the most critical on the retina as at this point there are sufficient number of rods to completely surround each of the diminishing number of cones. Retinal morphology at this point consists completely of eight rods around each cone octagonal “rosettes”. RW might note that this is a point of complete spatial order! I have pointed out on too many occasions that the only ratio of the sizes of cones to rods that can result in this geometry is 1.8:1 and that this corresponds to the visual band (700-400 nm).
I predicted that such measurements would show a preponderance of “green light detection centers”. It is at this angle that the density of rods is sufficient to completely surround each remaining cone and therefore response should be entirely green! Such measurements were made and reported in a paper (3832/A375) presented at the ARVO 2008 Annual Meeting titled “Arrangement of the Human Trichromatic Cone Mosaic in Peripheral Retina” and authored by O. Masuda, H. Hofer, J. Carroll and D.R.Williams. This work seemed to respond to my request extending the previous RW. work to larger retinal eccentricities. Results showed essentially what I had predicted in, what the authors termed, a “green cone clumping” effect at this angle. This “clumping” was noted as the first hint of a spatial order (of “cones”) on the retina.
To summarize, the light detection centers imaged by the authors do not correspond to a response of “cones” but rather the distances between receptors as the body of this work posits. There IS a spatial order to light detection center response on the retina and it corresponds to the three precise, circularly symmetric, single wavelength detection regions as explained in this work.
Seeing this finally makes clear the many historically unexplained conundrums of vision –a fundamental explanation for the formation of the visual image (in the Fourier domain), the never explained color constancy of vision, and, not unimportantly, the basis for color vision .
What more can I say!
GCH
Ojai,CA
3.24.10