More on the Ability of the Eye to Count Single Photons

by Gerald Huth on August 12, 2006

I have proposed substitution of the term ‘quantized interaction’ for the purely quantum term ‘ photon’ reflecting my understanding of visible light interaction with the biological retina of the eye that teaches that visible light is absorbed in finite nanostructural spaces or ‘antennas’  - i.e., as the wave of classical physics -  but necessarily adjacent to quantum-confined electron spaces that constitute the absorbing mass. Thus, neither the quantum or classical view of the interaction is violated.

There really can be no doubt that the eye at low light levels can detect at the photon level (the ‘quantum limit’), i.e., it can discern and discriminate single photons of light in the process of forming an image. What mechanism does it use to accomplish this feat at body temperature (+ 98 F) when our most advanced photonic technology requires cooling to cryogenic temperatures approaching absolute zero (-273 F)?

A few relevant numbers: Albert Rose (reference in an earlier Comment), using the only model available to him that viewed the eye as a camera, writes on p 32:

“The physical storage time of the eye is between 0.1 and 0.2 sec, and is probably closer to the latter. The physical storage time is the equivalent of exposure time in a photographic camera………”

Thus the ‘overall’, or what be termed ‘seemingly biologically possible, ’ time required by the eye to accumulate sufficient data for the eye-brain to acquire and discern that an image is ‘there’ is of this relatively slow magnitude. This is analogous to the ~1/20 sec ‘frame time’ of movies or television – images acquired in this time, when viewed in rapid succession, appears as motion. This is the time frame historically assumed by vision science – and by Rose the engineer. The only way to reconcile this with vision at the quantum limit is, as Rose had to assume, that a gain factor of a million must be present somewhere in the range from light interaction with the retina and registry of the signal in the brain. Such a gain factor is not, and has never been in evidence.

But how to reconcile this with the eye’s ability to detect at the quantum limit?

The answer must lie in distinguishing two separate times differentiating between: 1.) an initial time ‘sufficient to accumulate events on the retina that results in a required information content’, and 2.) a second ‘biologically slow time where information constituting the entire image is transferred in one discrete package forward to the brain’. The latter presents no problem as it refers to the slow time described above and is consistent with, or constitutes, the image formation time discussed by Rose.

What is new, the ‘initial time’ of 1.) above would be defined by light interaction at the ‘front end’ or with the retinal outer segments as defined in this work. More specifically, this time would encompass the interaction event and isomerization of the retinal molecules contained within each receptor. I propose that an ‘electronically viable signal’ would result in this process that wold form one picture element of the acquired image.





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