A Signal Event in History! Recognition that the Retina is the Fourier Plane of the Eye!
January 16th, 2007 | No Comments »Harris (”Rewiring Neuroscience - What Does a Memory Look Like”) in proposing that the retina forms the Fourier (focal or diffraction) plane of the eye points out correctly that Figure 4 of my original paper “What the All-Cone Fovea Images Solely at Long Wavelength” is misleading. I used an optical transform (the only means that we poor humans have of visualizing a Fourier transform!) from Caulfield to illustrate the point that the transform of an outline sketch is primarily (the key word!) a small central spot - that I associated with long wavelength interactions and the central fovea.
What I did not note was that the high spatial frequency information associated with edges of the line drawn sketch was encoded in the outer reaches of the transform. Since there is not much information in the sketch itself (most of the field is uniform white) this part of the transform is almost invisible.
Harris goes on to note (again correctly) that the bright central spot encodes low spatial frequency information associated with intensity-only term of the Fourier equation. He terms this “throw away” information but I don’t believe that this is true. Nature rarely seems to deal in useless information. Rather I think that this might add something to my thoughts.
First, I have proposed that the visual process takes place in the area from the central fovea to approximately twenty degrees of retinal angle. This would be approximately the extent of the high frequency information encoded in the transform noted above. Remember that beyond this angle, i.e., the entire peripheral retina, acts as a short wavelength-defined, wide angle ‘light meter’ controlling pupillary constriction and overall light entrance into the eye and the sensitive retinal Fourier plane. Even with this situation there would still seem to be a need for a brightness (i.e., ‘intensity’) controlling signal for processing the visual image. I might believe that this is the role played by this central part of the transform.
I have probably been misleading in other statements to the effect that this transform (to be precise henceforward: ‘the long wavelength transform’) encodes the ‘outline sketch’ (that I have termed the ‘Marr sketch’) of the perceived image on the fovea. It does encode such a sketch but not directly on the fovea! This was misleading!
GCH
1/16/07
