THE TIME DOMAIN AND THE QUANTUM NATURE OF THE VISION PROCESS
November 25th, 2008 | No Comments »
To anyone following this work it will be clear that I believe that the primary process (or processes) of vision – interaction of light with the nanostructure formed by retinal outer segments – occurs in the spatial near field and in the femtosecond (10-15 sec) time domain. That, what is termed the primary chemical event in the vision process – isomerization of the rhodopsin chromophore within the body of the retinal receptor - occurs in femtoseconds has been known since the late 1980’s. A reference chosen from many:
“The First Step in Vision: Femtosecond Isomerization of Rhodopsin” RW Schoenlein, LA Peteanu, RA Mathies, and CV Shank Science, Vol 254, Issue 5030, 412-415, (1991)
Lawrence Berkeley Laboratory, University of California, Berkeley 94720.
ABSTRACT
“The kinetics of the primary event in vision have been resolved with the use of femtosecond optical measurement techniques. The 11-cis retinal prosthetic group of rhodopsin is excited with a 35-femtosecond pump pulse at 500 nanometers, and the transient changes in absorption are measured between 450 and 580 nanometers with a 10-femtosecond probe pulse. Within 200 femtoseconds, an increased absorption is observed between 540 and 580 nanometers, indicating the formation of photoproduct on this time scale. These measurements demonstrate that the first step in vision, the 11-cis—-11-trans torsional isomerization of the rhodopsin chromophore, is essentially complete in only 200 femtoseconds.” (underline is mine).
Now to define this retinal nanostructure – forget the idea of cones and rods and view it abstractly as a two dimensional array of quantum confined electrons in the near field of light. We are viewing then, in essence, a quantum structure!
As we enter the nanostructural era, and our ability to make measurements in the femtosecond time domain matures, we might expect to find new processes – quantum processes - at work in processing of visual information.
Even now such new experimental results are being reported corroborating the . A recent paper by University of California investigators is one such result. The reference:
”Evidence for Wavelike Energy Transfer Through Quantum Coherence in Photosynthetic Systems” , Engel G.S. et al,. Nature, Volume 446, Issue 7137, pp. 782-786 (2007)
PORTIONS OF ABSTRACT:
“Photosynthetic complexes are exquisitely tuned to capture solar light efficiently, and then transmit the excitation energy to reaction centres, where long term energy storage is initiated. The energy transfer mechanism is often described by semiclassical models that invoke `hopping’ of excited-state populations along discrete energy levels……….
….But the intricate dynamics of quantum coherence, which has no classical analogue, was largely neglected in the analyses-even though electronic energy transfer involving oscillatory populations of donors and acceptors was first discussed more than 70 years ago, and electronic quantum beats arising from quantum coherence in photosynthetic complexes have been predicted and indirectly observed. Here we extend previous two-dimensional electronic spectroscopy investigations of the FMO bacteriochlorophyll complex, and obtain direct evidence for remarkably long-lived electronic quantum coherence playing an important part in energy transfer processes within this system. The quantum coherence manifests itself in characteristic, directly observable quantum beating signals among the excitons within the Chlorobium tepidum FMO complex at 77K. This wavelike characteristic of the energy transfer within the photosynthetic complex can explain its extreme efficiency, in that it allows the complexes to sample vast areas of phase space to find the most efficient path.”
(I would not agree with the last sentence that I have underlined… “allows the complexes to sample”….NO!…. / GCH )
The fundamental point of this work I believe is that a new phenomenon – quantum coherence- has been introduced into, and shown to be operative in, the light energy absorption process. It seems not too much of a leap to see how this mechanism might be at work in light interaction with the quantum retinal nanostructure as noted above.
Entirely new mechanisms at work in the femtosecond time domain with all that this portends for the capability for processing information!
A note – I have proposed and shown specifically how – the nanostructural retina is deployed in the photosynthetic apparatus of the world of plants and algae. The photoreceptive apparati of biological vision and plant photosynthesis use the same fundamental nanostructural principle.
Think !!!!
GCH
11.25.08
