The Vision Process Involves Two Separate Time Domains
September 22nd, 2006 | No Comments »
I will begin by repeating the quote from Albert Rose’s treatise “Vision Human and Electronic” (Plenum Press) p.29 (emphasis mine):
“In the scheme of evolution, vision has an almost unique role. One can conceive, for example, that further evolutionary developments might lead to a larger brain capacity, a more evolved nervous system, or a variety of enhancements of current functions. It is not conceivable that the sensitivity of the visual process can be significantly enhanced. The visual process is at an absolute terminal point in the evolutionary chain. To the extent that the visual process now succeeds in counting each absorbed photon….”
This ability of the vision process has never been explained and seems never to have elicited interest to the vision field.
A summary:
I have been fascinated with the idea that in looking at an object only a foot in front of me I am “looking into the past”. Light reflected from that object to my eye requires a nanosecond (10-9 sec.) to arrive at my retina so that I can tell only what happened to that object a nanosecond ago. I can never see it “instantly”. Inherent in this mental exercise is the idea that my eye “passively” receives this image on the retina subsequently transiting it to the brain, my consciousness etc. with time not being considered in the process.
But time is inherent in the process of vision.
I will proceed in the next few days to lay out an entirely new logic for the process of vision that follows from a physical explanation for the eye’s ability to sense single quanta. To achieve this level of sensitivity the vast retinal array, must be considered to be composed of individually acting receptors or “light detection devices” (defined as the receptor appositions that I postulate) each of which can detect and generate a measurable signal from the interaction of single quanta (the “quantum limit”). I will show that receptor appositions form such devices with a reaction time in the picosecond (10-12 sec) time domain (with reaction time being defined as the time between light “stopping” in the mass of the detection center and the generation of an electrically measurable signal for subsequent use in the image formation process).
The retinal array (comprising 200,000+ independent devices in the fovea alone) of quantal signals thus derived forms a near instantaneous image in this fast time domain on the retinal surface.. This “entire quantal image” continuously “updates” a spatially and temporally coherent image stream (?) being transferred via the optic nerve. to the visual centers of the brain The optic nerve is composed of 1.9 million separate fibers appearing as a coherent (i.e., imaging) fiber bundle Transmission of the image through the optic nerve is ionic and therefore slow (10-3 sec or millisecond) time. This slow mode of transport combined with the finite length of the optic nerve combine to “slow the visual image to human scale proportions”, i.e., compatible with the time scale in which nerve signals can reach extremities etc. I propose that this time is the genesis of the incorrect idea that the “reaction time of the eye” is from 0.1 to 0.2 seconds.
(It intrigues me that evolution must have defined the length of the optic nerve, i.e., the physical distance from eye to brain to bring the “instantaneous” quantal visual image into a time scale useful to human proportions!)
Therefore, I believe that the visual image is actually detected and processed in two separate time scales : 1. initially )in the picosecond or fast time domain in which the quantal image is latent on the retina and, 2. a secondary, millisecond, time domain introduced by transport through the optic nerve to transfer the intact image into a slower time useful to the human system.
I propose therefore that the eye, in contrast to what been historically believed, actually views a “progressing ephemeral instant” of time that is subsequently slowed for compatibility with the human system. The former is of interest to physics with the latter slower time domain of concern to biology.
It should be obvious that even within the process of vision itself we are “looking back in time”. We are doomed by the design of the human system itself to always view the past! Might this be the underlying reason for the physics conundrum of a direction or “arrow” of time?
Finally perhaps this explanation provides some insight into the “instant” that has been of interest to philosophers over the ages (and the physicist Julian Barbour). And moreover……there are some four orders of magnitude between the picosecond time domain invoked here and the frequency of light. What information might be contained in that span of time?
This is meant to be a quickly written summary written on a Friday afternoon. I will follow in the coming days with supporting data as to the speed of response requirement of retinal detection devices. Etc.
GCH / 9/22/06/revised 9/23/06
