Rethinking the Process of Vision

One of the rarely mentioned problems relating to the eye and vision is that the eye is capable of sensing individual photons (I would term these ‘quantum interactions’..more about this below). Further, this feat astonishingly is accomplished with the organ at the elevated, body temperature of 98F! We are able to accomplish this same feat technologically using silicon photodetectors but only if the detector is cryogenically cooled to a few degrees above absolute zero (i.e., -273K) and, even at room temperature, using high voltage (not available to the eye) and a vacuum photomultiplier tube. This ability of the biological system is thus quite extraordinary with the mechanism involved never having been explained - or even much discussed in the literature.

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A NOTE: The reader will remember that it is actually obvious from this view of light interaction with the eye that the eye evolved to detect light as a wave - the wave of classical physics. But now the new insight - that this interaction occurs adjacent to what are termed ‘quantum confined electron sites’ that correspond to the retinal receptors. It is my view that the interaction should therefore properly be termed a ‘quantum interaction’. The modern, ‘pure quantum’ view that a ‘photon interacts with something..’ is really a dead end in the thought process - and the eye teaches otherwise! I will herein use the term photon, because it is so termed in the references that I use, but the reader should understand it as a ‘quantized light interaction’
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Albert Rose in a text describing a technological approach to the vision process (“Vision, Human and Electronic”, Plenum Press, 1974) wondered about this and discussed the single photon detection capability of the eye from an electronic viewpoint. Rose states (p.41) “light absorbed by the retina…..one must conclude that the efficiency of the eye is essentially 100%. In brief, the eye is able to count each absorbed photon” (emphasis mine). This is a very dramatic statement about which I will have more to say shortly. As is well known the eye is sensitive to very low levels of light but it has not been assumed that it is capable of separately detecting and discriminating between each individual photon!

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I cannot stop myself from quoting a line from p.1 of Rose’s text:

“It would be difficult to find a more cogent confrontation between physics and biology than in the visual process”.
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Rose’s conclusion following from his background in electronics (he was the inventor of the Vidicon tube that had such impact on the development of television!). This led him to propose that an amplification (or electronic ‘gain’) of the original photon interaction signal of a million (a factor of 10⁶)’ must somehow be operative in the eye. This is one way to express the system requirement for single photon detection but there are others. Rose could provide no idea as to how the biological eye might accomplish such amplification.

Any signal detection process involves two factors – the inherent (or original) signal level balanced against the random electronic noise that might interfere with (or obscure) that signal level in the overall detection system. One must achieve an adequate ‘signal-to-noise ratio’ for unambiguous detection of an event. Accepting the original signal level and reducing whatever noise might be present is another strategy for low level signal (such as single photon) detection.

First, what constitutes the ‘fundamental signal’ when a light wave interacts with an ‘antenna’ absorbing site on the retina as I propose. Such centers (or ‘devices’) are comprised of two adjacent receptors (or more precisely, the quantum- confined electron spaces that the receptors provide) and the wavelength-defining space between them. Light interacts as the wave of classical physics in this central space imparting a different amount of energy to each receptor (with the difference a function of the direction that the light ray entered the device) The energy thus imparted then mechanically/electrically effects the isomerization of the retinal molecules contained within each receptor from the cis- to trans- state. This then constitutes the initial ‘signal’ that must subsequently processed to provide the visual image.

Let’s take a minute to discuss this most fundamental light detecting device. First, it is extremely small having a cross section smaller than light wavelength and length the dimension of the receptor outer segments (~50 microns). The time response of any electronic device is dependent upon its dimensions. This is the reason why microcircuitry technology is always seeking smaller ‘feature size’ (i.e., smaller devices) to satisfy the ever present need for increased speed. The charge stopping time (or the time when the signal is ‘there’) I estimate for a device of this dimension to be of the order of 10^-12 seconds (or a picosecond). This is an important number and I note that it has nothing to do with subsequent, much slower, biological signal processing or transduction time in sub-retinal circuitry or in the brain.

Thus, one must imagine a retinal array of these very fast devices. I would contend that the initial (and complete) information to form the visual image is present on the retina in picosecond ( 10^-12 second) time.

Now back to the subject of ‘signal to noise’ ratio:

Every radiation detection system has an inherent ‘time constant’ that can be considered a ‘time window’ that is ‘left open’ long enough for the signal to be recognized as such and, for example, be electronically transferable to an ‘amplification stage’ for further processing. One property of this ‘time window’ is that electronic noise in the system (i.e., random electron events coming in time) are integrated. The longer the time window is left open the higher the noise that is accumulated within the window. This ultimately constitutes the noise level that obscures the signal. The fundamental rule is therefore that one wants the overall act of detection to be accomplished in as short a time as possible, ideally in a time approaching the ‘signal-is-there’ time

A number of us published a paper on the subject of this optimization in 1976

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Tove,P.A., Cho,Z.H., Huth,G.C., “The Importance of the Time Scale in Radiation Detection Exemplified by Comparing Conventional and Avalanche Semiconductor Detectors”, Physica Scripta, 13, 83-92, (1976).
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I will not go into details of this work here but only to note that the relevant time constant of detection systems of the time was in the microsecond (10^-6 sec.) range. Thus the ‘time window’ was left open for some six orders of magnitude longer than desirable accumulating noise and raising the level of signal that could be detected.

Now to the eye. Validating the 1935 retinal measurements of Osterberg, I have shown that the retina forms the focal or Fourier plane of the converging lens system of the eye. There really can be no doubt about this. It is a property of this plane, as Feynman so cogently explained, that light rays are brought into ‘time convergence’ at this point with light rays that pass through the center of the lens being slowed to allow refracted rays from the thinner outer part of the lens to ‘catch up’. I have written about this elsewhere on this page.

The central fovea of the retina can be used as the prime example with all light rays entering the eye brought to such a time convergence at this point. I have written that such time ‘convergence’ might be defined as ‘zero time’ (or as near as quantum limitations will allow) or what might be thought of as the ‘the absence of time’ or the ‘instant’ of time. Thus the visual ‘signal’ comes as close to the optimum time described above as one might imagine.

The light detection devices of the retina are thus seen to be consistent with the time requirements of Fourier plane imaging so, in fact, the entire content of information necessary to form the visual image is ‘there’ in picosecond time.

I believe that the invocation of the picosecond time domain answers the question as to how the eye detects single quantum events. It is not that the signal is somehow amplified but rather that the contravening noise level is reduced.

With the above insight as to the time regime, it occurs to me that the terminology of ‘detecting single quantum events’ is not strictly correct. This capability might more properly be termed that the ability of the eye to ‘discriminate in time the interaction of single quantum events’. As I have shown the retina is capable of logic function in the picosecond time domain. This opens up many new avenues of thought.

For example, I believe that analysis will show that at normal light levels entering the pupillarily (?) constricted eye the individual devices of the retina will be able to separate individual quantum events. I am working on this.

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Reading beautiful text from Oliver Sacks (“The Man Who Mistook His Wife for a Hat”, Touchstone).

To wit from p.148 (all italics are in the original text):

“Experience is not possible until it is organized iconically; action is not possible until it is organized iconically. ‘ The brains record’ of everything – everything alive – must be iconic. This is the final form of the brain’s record, even though the preliminary form may be computational or programmatic. The final form of cerebral representation must be, or allow, ‘art’ – the artful scenery and melody of experience and action”.

Does not invocation of the time domain as I have introduced open up new lines of thought? Might even more information (for example, required to encompass the iconic state that Sacks describes) be found to be contained within the visual image at even shorter times - within the wavelength of visible light or from ~ 10¹⁴ to 10¹⁵ Hz. Millions of cycles of light interact with the length of each retinal device… might information (intelligence) be contained in this even shorter time domain?

Might the basis for the concept of a ‘holographic mind’ follow from this thinking?.

I feel again compelled to answer what I believe will be the biologists objections to this entire time domain argument, namely, that biological processes are too slow etc. Understand that I propose that the ‘virgin’ visual image information is there, for all intents and purposes, instantly. The ENTIRE image can then be SIMULTANEOUSLY ‘carried forward’ in any slower, biologically compatible, time domain without invalidating my proposal.

GCH

7/26/06

GCH

7/24/06

If one can gather in this simple concept of light interaction with the retina of the eye one sees that the fundamental principle involved is that this biological structure evolved to conform to an exact geometrical symmetry. Moreover, this geometrical symmetry overlays the characteristically indefinite structure characteristic of biology and, specifically, of this biological organ. A precise physical principle seems the basis of the biological realm to which evolution conforms!

(I have noted over and over that the admixture of the two sizes of retinal receptors, i.e., the cones and rods, forming the retina are in the ratio of the visible band (1.8:1 or 700-400 nm) and the apposition of one size receptor to the other (i.e., a cone to a rod) defines exact midband. This occurs on the retina at an angle of 7-8 degrees where midband wavelengths are refracted by the structure of the eye.)

The specification of such a geometric center, from which other factors such as wavelength are referenced, explains the color constancy of vision and provides the fixed ‘fulcrum’ necessary to explain Edwin Land’s color vision experiments.

Thus the refraction of light within the eye combined with this geometric principle defines a wavelength of 550 nanometers!
What deeper meaning might this finding have? Might considerations of geometrical symmetry be propagated further on via the pathways conducting visual information to the brain and perhaps lead to new explanations for brain function?

GCH