Rethinking the Process of Vision

This model concludes that it is the long and short wavelength limits and exact mid-point of the visible band that are detected by the outer segment of the retina. This conclusion is arrived at by combining a.) the long accepted distribution of cones and rods on the retinal surface, b.) the optically refractive properties of the structure of the eye and, c.) the assumption that light interacts as a classical wave with spatial “antenna” dimensionalities.

Specific wavelengths absorbed by the retina are determined by the dimensionalities of the three retinal receptor appositions (i.e., cone-cone. cone-rod, and rod-rod). This is summarized in the following figure that might be termed the “Rosetta Stone” of retinal light absorption.

Trichromicity is therefore a logical consequence of the specific distribution of cones and rods on the retinal surface. Vision is trichromatic but not at all for the reasons previously assumed.We propose that from first principles these wavelengths define the precise long (700 nm) and short (400 nm) wavelength endpoints and, importantly, the exact center (~ 550 nm) of the visible band and represent the fundamental definition of “primary” colors- red,green and blue.

The first stage of the detection process in vision then uses these three cardinal points to perform a “color separation” of the perceived image into three separate optical or Fourier transforms. I propose that David Marr’s “primal sketch” is detected as one optical transform effected at the all-cone fovea using the narrow long wavelength (red) band. A signal synthesized from a comparison of the response from the two regions on either side of the geometrically determined midpoint provides for the total sensation of color. This comparative signal is the basis for Land’s deduction that color was derived from a “comparison of lightnesses” around a somehow fixed “fulcrum” that we now geometrically determine actually exists at a retinal angle of 7.5 degrees. This would seem to provide an explanation for the controversy that charged Land with abandoning trichromicity and proposing a “two color system” for the visual process (which he always denied). It is now clear that three wavelengths are involved (the gamut of color) but that color is determined around a fixed intermediate wherein two wavelength signals are compared. The mix up that generated the controversy becomes clear. Land was right!

The color constancy of vision is seen to be a logical consequence. It would be very helpful if use of the term “color” (other than the three primary colors) in describing retinal function were diminished and it was understood that this sensation derives from a synthesized signal transmitted from the retina to the color centers of the brain as Land proposed.

Ewald Hering’s contribution in the light of this new model seems to have been an attempt to correct for the not quite complete separation of primary colors on the retina. He added and/or subtracted colors to obtain, in the eye of the observer, the purest primary colors. He termed these “opponent wavelengths”.

Although it will not be obvious until one studies the paper, it is uniquely the presence of two sizes of receptors admixed on the retinal surface determining a geometric mid band point that allows the sensation of color to be perceived. VISION IS TRICHROMATIC ONLY BECAUSE THE HUMAN RETINA CONTAINS TWO SIZES OF RECEPTORS! This predicts that any specie with only one size of receptor will have only a very narrow window of vision - and no sensation of color.

The retina is not therefore composed of ‘pigmented color-sensing receptors’…. cone receptors do not ‘detect color’….rod receptors are not ‘low light level’ sensors….as someone in vision science once commented to me ‘no one believes these things anymore’…although they are still in every textbook!

The refractive properties of the eye are in consonance with this proposal …what has been considered an aberration…..’longitudinal chromatic aberration’ is not an aberration at all but functions to direct light wavelengths to the precise areas of the retina predicted here.

The octagonal symmetry of rods-around-cones at the midband point (at a retinal angle of ~ 7.5 degrees) besides setting the bandwidth of the system, must represent the diffraction pattern of reality perceived by the eye(moreover, the ratio of the sizes of cones to rods on the human retina is 1.8:1 which corresponds to the perceived bandwidth …700 to 400 nanometers…?). This same octagonal symmetry is present in the visual organs of most (all?) species and is even present in the lateral organization of the chloroplast organelle in photosynthesizing plants. For the physics minded, this geometric symmetry represents the spatial embodiment of the visual band of wavelengths - the frequency-to-space conversion of the Fourier transform!

I believe that the technology is now available with the discovery of visible light interactive ‘porous silicon’ (which uses the same optical interaction principle as the retina ) to begin development of an artificial vision chip that truly mimics it’s biological counterpart. Such a chip would seem to me to be consistent with what must be the organization of the underlying neuro-circuitry of the retina and would have a great chance of being successful.

Also, development of porous silicon should proceed with the goal of fabricating “smart pixels” (i.e., with the capability of detecting both light intensity and phase as the biological retina). It seems to me that this would lead to fundamentally new imaging technologies embodying, for example, the color constancy characteristic of the vision process.

I believe that the same nano-geometric organizational principles evolved by the eye to detect light are evident in the structures of photosynthesizing plants and algae. In such biological organisms light collection efficiency is the predominant consideration so that the same nano-geometrical structures are organized in broad lamellae.