Rethinking the Process of Vision

The “first” process that occurs as light enters the eye is the spatial Fourier transform performed by the condensing lens of the eye’s structure. Refraction from the lens and body of the eye result in the visible spectrum being focused at different points slightly above the retina. This has historically been improperly termed chromatic “aberration”. Retinal receptors evolved to detect (or “interrogate”) three discrete points on this spectrum… the long and short wavelength endpoints and the exact center of the band. These points, so defined, represent in the time domain the three primary color signals that are at this point distinctly separated in time. Precisely, the long wavelength endpoint (red) does come to focus at the fovea of the retina and might be termed the “first time” or”reference time”. This is probably the genesis of David Marr’s observation. The other two components of the eventual image (mid-band green and blue) come to focus at some distance above the retina. It is important to consider that these points represent (probably within quantum limits) “zero time” or “instants of time”. This is the result of the first “spatial” Fourier transform. However, in the time domain, the information content of these green and blue foci must travel different finite spatial distances before reaching the retina.

Now, a second inverse Fourier transform must somehow be accomplished to arrive at an image. This means that somehow the three signals must arrive at the retina in coincidence… not sequentially as the above implies. Somehow there must be some effect in the time domain that is analogous to the above described condensing lens of the spatial domain. Such a mechanism is not in evidence. ???

I would note again that I believe that the concept of separating the three signals in the time domain is important. One might consider them “starting points” for the eventual synthesis of an image. This has nothing to do with any much slower “biological image processing time” that may subsequently ensue.

This entry was posted on Monday, July 25th, 2005 at 3:02 pm and is filed under Color Vision, Fovea, Retina, Running Commentary . You can follow any responses to this entry through the RSS 2.0 feed. You can leave a comment, or trackback from your own site.