Rethinking the Process of Vision

I have received a number of requests to summarize this explanation of the vision process. This is another attempt to do so / GCH

The initial text here uses  two figures excerpted from the original paper (available on webpage) and forms the fundamental basis for the explanation. All follows from this argument.

The first figure attributed to Osterberg recounting the distribution of cones and rods on the retinal surface is referenced in countless textbooks on vision.  There can be no doubt that these measurements have been accepted by vision science. One notes (although it is not clear in the drawing)  that most of the cone receptors, in fact greater than 99%, are contained in only one degree of retinal angle.  This small region is  termed the fovea.  As one proceeds to retinal angles beyond one degree it is seen that rod receptors are introduced  into the dense (hexagonally packed) array of cones in a statistically distributed manner. The accepted model states that it is the array of cone receptors functions to “detect color”.  It has been historically assumed that, in agreement with the known trichromicity of vision, there must be three “classes” of color sensitive cones - commonly termed as red, green and blue sensitive. Now, keep in mind that >99% of all of the cones reside in the small central foveal region - within the narrow one degree retinal angle.  Vision science goes on from here to assume from that the retina represents the intensity-only sensitive image plane of the optics of the eye. This is the plane where film is located in a camera. To imagine how these cones might form an image they must display some spatial order as in the regular array of RGB triads or stripes on a television screen  or in the imaging chips used in digital cameras. But….none of this appears on the retina! The proposed RGB sensitive cones are haphazardly distributed with no discernible order…and, moreover, the blue or “B” sensitive cones have a difficult time making an appearance at all !

I believe that this describes the paradigm that has evolved in vision science . Even on the face of it, is in my view totally irrational.

It is the accepted Osterberg data that forms the fundamental basis for my explanation.

A logical interpretation of  Osterberg’s  measurement  in this work proposes that  it  is the distribution of receptor appositions that defines sites where light  wavelengths interact on the retinal surface. It is not “photons interacting with pigment molecules within receptors” but rather light interacting as  the wave of clasical physics interacting in antenna fashon between adjacent receptors. As presented in the original paper, a simple counting (i.e., cone-cone, cone-rod, rod-rod) of these appositions as a function of retinal angle reveals a diffraction the light sensitive surface that underlies the trichromicity of vision. This, in turn, reveals that the retina is actually a diffractive  surface forming the  Fourier (or focal) plane of the optics of the eye and not the intensity-only or “camera film” surface that has for so long been presumed.

This is the fundamental essence of all that  follows!

The retina of the eye, and specifically the plane of retinal outer segments, is seen to be composed of an array of more than 130 million logically spaced light detection elements (or pixels)  that function to translate incident electromagnetic wave radiation into quantized electron particles.  These elements function in the near-field ( i.e., of dimensions smaller than light wavelength) and in times as short as femtoseconds ( 10-15 sec) . The quantized electrons encode the electrical information necessary to form the visual image. The historically defined cone and rod receptors are seen to function as generic structural elements that function  to provide the required spacing between adjacent receptors. The ratio of the diameters of these two sizes of receptors actually corresponds to the visual band, i.e., the ratio of  -1.8:1 corresponding to the 700-400 nanometer visible band. We must stop thinking of  receptors as cones and rods with different functions and realize that they represent simply two  sizes of  generic light conversion elements.

The lateral spacing of this nanowire array is determined by a simple geometric rule that selects  three wavelengths from the broader electromagnetic spectrum for detection in the vision process. These are the same three wavelengths that have historically  been termed primary that underlie the correctly understood trichromicity of vision

This geometric  rule derived from the retina states that: an admixture of circles of two diameters defines three center-to-center wavelength-determining dimensions with the ratio of these two diameters defining the detected bandwidth.

Further, these three wavelengths are pre-selected  by the light refractive chromatic aberrration of the structure of the evolved eye and focused onto the retina. This refraction has been historically and improperly termed an aberration but it is not an aberration at all but is fundamental to the visual image formation process.

In the largest sense then it then becomes clear that the true nature of the vision process is an objectification of the basic laws of the refraction of light and that the biological morphology of the retina evolved from simple and well understood molecular (chemical/polar lipid) self-organization mechanisms.  Paraphrasing LaPlace  “There is no need for a creationism hypothesis”.

The three wavelengths detected by the retina  have  historically been correctly defined as primary but  improperly termed as colors. Early vision science discerned the  trichromicity of vision  but from that point picked the wrong model to explain it.

Thus, at the basis of evolved biological vision is a nanostructure that geometrically selects three wavelengths from the broader electromagnetic spectrum and translates these into quantized electronic information that is used to form the visual image.

The nanostructure of the retina  evolved to detect light as an electromagnetic wave with the quantum transition to electron particle occurring at the point of retinal outer segments. The result instead of imagining that  “a photon interacts…” should properly be termed more generally that a  quantized interaction occurs.  The traditionally used construction that photons interact with pigment molecules within retinal receptors was always inaccurate.  And further, it is not and never was the case that “photons go from place to place”.

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For a discussion of the history of the concept of a photon read the paper “Anti-photon” by Nobelist Willis Lamb(Appl.Phys, B 77-84, 1995)

From  the abstract of that paper.

“It should be apparent from the title of this article that the author does not like the use of the word “photon”, which dates from 1926. In his view, there is no such thing as a photon. Only a comedy of errors and historical accidents led to its popularity among physicists and optical scientists……”

So there!!!

But Richard Feynman believed in photons !  …  from his “QED” p.15:

“I want to emphasize that light comes in this form - particles. It is very important to know that light behaves like particles, especially for those of you who have not gone to school. where you were probably told something about light behaving like waves. I’m telling the way it does behave - like particles.” (emphasis from F.)

This is like being told that there is no Santa Claus!

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Further, it must be emphasized that the individual light detection centers of the retinal array have dimensions smaller than light wavelength (i.e., they function in what is termed in physics the near field) and in a time scale of femtoseconds (10^-15 seconds). These centers therefore serve to effect a fundamental quantized spacetime translation from wave to particle.

Following the initial light absorption process, energy is transported laterally (i.e., parallel to the plane of the retinal surface) along the lipid membrane that forms the structure of the thylakoid disks within receptors. This energy transport occurs via a phononic  (or, as I propose, lossless solitonic ) mechanism that serves to thermalize the absorbed energy  slowing the process down to human nervous system proportions, i.e., near millisecond (10^-3 seconds). What has been termed the millisecond reaction time of the eye was always actually the reaction time of the human nervous system and not the eye itself.

Thus, the traditional morphological distinction between cones and rods can be finally understood. The function of the opsin protein moiety of the rhodopsin complex contained within receptors is actually structural with the purpose of it’s various perturbations being to effect the variable wavelength-defining spacing of the retinal array. Also finally explained is the, what has been termed,  anomalous, dichroism of the rhodopsin light-accepting complex. We can now make sense of the laterally directed orientation of this molecular complex.

The incorrect idea that “cones detect color” and “rods detect black and white” quoted in  every textbook on vision can now discarded. Use of the terms “primary” (as  noted above) and “color” are now understood. The retina geometrically detects three primary wavelengths with the term “color” reserved to describe the synthesis of hues from these wavelengths as elegantly described by Edwin Land - when is someone going to realize this! Not unimportant in this regard is the finding of this work that the exact midpoint (near 550 nanometer) of the visual band  that vision uses  for “Land color synthesis” is geometrically determined. In one stroke a large part of the image forming logic used by the eye in vision is explained.

In summary, it can be seen that the “first stage” of the vision process functions in the realm of quantum physics with all that this portends.

One then imagines that we humans “peer out”  into the broad electromagnetic spectrum that surrounds us through three narrow biologically evolved wavelength filters gathering information from that as yet only dimly understood regime of quantum physics - but we can now be sure that this is the case!.

The future of our understanding of the vision process seems  linked to the domain of quantum physics.

GCH

Ojai, CA

This entry was posted on Sunday, November 30th, 2008 at 3:02 pm and is filed under Running Commentary . You can follow any responses to this entry through the RSS 2.0 feed. You can leave a comment, or trackback from your own site.