Rethinking the Process of Vision

A summary - this explanation for light interaction with the retina shows that the rods of the peripheral retina (i.e., beyond twenty degrees of retinal angle) are not a part of the image forming process but are linked to act as a wide angle “light meter” whose function is to measure the light input into the eye. In association with the finding that the dimensionality of  rod-to-rod appositions defines blue sensitivity it follows that blue wavelengths must be involved in constriction of the pupil of the eye and there seems to be ample evidence in the literature for this assertion. Further, I propose that this pupillary, control being a mechanical action will perforce have a slower time constant than the purely electronic interactions of other wavelengths with the retina - red wavelengths interacting with the fovea for example. It seems to me therefore  that an antagonism  is inevitable  in the  visual signal transmitted to the brain arising from a flickering light input of long and short wavelengths. There would be a continuous effort by the pupil-controlling blue end of the spectrum attempting to “keep in step” with a longer wavelength signal.

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The condition of epilepsy is generally  described  and studied from the viewpoint of association with the electrical activity of the brain. There is, however, a literature and experience connecting  this condition , or perhaps more properly the initiation thereof,  to visual effects. I  recently became aware of possible effects on human behavior associated with proximity to the new energy saving CFL (”Compact Fluorescent Light”) lighting devices.

I have previously written (July 2005) on the subject of pupillary constriction.The following is an updated version of that text.

ON PUPILLARY CONSTRICTION

Although it doesn’t seem to be widely recognized, a recent paper Drew et al (Pupillary Response to Chromatic Flicker, Exp. Brain Res.136, pp 256-262, 2001 ) finds that it is the wavelength (hue or color)   and not the intensity (luminence) of light that is the determining factor in constriction of the pupil of the eye. In my explanation for  retinal light interaction the integrated response of the rods of the peripheral retina acting as a “wide angle light meter” (which we assert is sensitive solely to short wavelength radiation) that controls this function.

The question that follows is what are the most effective wavelengths? Drew et al after finding that hue (color) modulated flicker has a much greater effect on constriction than a luminance modulated signal found that: “Red-blue color-paired flicker consistently produced the strongest (pupillary) constrictions. These responses occurred even when the flicker was of a lower luminance, both physically and perceptually, than a preceding non-flickering color, indicating that chromatic rather than luminance-sensitive mechanisms are involved in this response.”(emphasis mine)

Additionally, Drew et al point their results to the condition of “photosensitivity…in which afflicted individuals are abnormally sensitive to particular forms of photic stimulation which can result in seizure attacks…” Interestingly, they cite an event that occurred in Japan where 700 children were hospitalized after watching a television program where a particular red-blue flicker signal was displayed. (again emphasis is mine)

My explanation for light interaction with the retina may give some insight into the mechanism involved here. In this explanation  red wavelengths  are solely refracted to the all-cone fovea. Signals arising from these interactions would be very fast due to their purely electronic nature. (I have more recently proposed that at least the first light interaction event of the interaction process would be in the femtosecond or 10-15 sec time domain).   The time constant of the periphral blue-sensitive “light meter” array of rods, on the other hand, would have a different (perhaps vastly different) time constant  associated with its function of controlling the pupil of the eye. The mechanical nature of this process predicts a slow speed of response - much slower than the electronic long wavelength signal.

From the above one can almost envision a chaotic situation that arises where the slower process of pupillary constriction is attempting to “keep up” with  fast  long wavelength signal. I would think that this would disrupt  the otherwise coherent interplay of these two signals presented to the brain. Might this explain the effects described by Drew?

There are some  testable predictions that can be made from these conclusions. The first might be that the farther the flickering wavelengths are apart the greater the effect on the brain and behavior… with red and blue representing the ends of the visible spectrum…the more pronounced the effect. There is also consideration of the width of the spectral peaks  that are involved in the flicker. I must remind that there are absolutes here that follow from my explanation…the precise and constant separation distance of the foveal cones represents the absolute long wavelength limit of visual response. The corresponding separation of rods (center-to-center distance) defines the absolute short wavelength limit of this response. These a precise geometric conclusions.

It may then be that an ultimate red/blue, i.e., corresponding to the ends of the visible spectrum, separation of wavelengths leads to the ultimate condition of an epileptic seizure  (testable?).  Might lesser separations lead to lesser, perhaps disorienting, effects? And, we come to the subject of CFL’s.

A simple Google search  of “epilepsy vision”  finds many citations with the following non-scientific but informative link Energy Saving Lamps an example. One immediately sees that light emission from the phosphors of CFL’s consists of a series of narrow peaks. One gains the impression that these peaks seem generally, in commercial lighting, to be three in number at  wavelengths of approximately 425, 550 and 600 nanometers. I might guess that this is the result adding additional long wavelength emitting phosphors to “soften” (i.e. turn “reddish”) the bluish cast of a basic phosphor.(that may be ZnS?).  The light output of  traditional fluorescent lamps is also composed of peaks at approximately the same wavelengths. For comparison, the corresponding light output from a tungsten lamp is a continuum of wavelengths stretching from 400 to 700 nanometers. A “white light” LED lamp has a single peak at 460 nanometers.

I might speculate that the spectral output of CFL’s (and fluorescent lighting) has at least the potential for producing effects such as seen by Drew.

There is much more to be investigated here. The time domain of the flicker will surely be important.

GCH

6.03.08