Rethinking the Process of Vision

As a scientist I have been saddened by the treatment accorded Edwin Land and his work on color vision in the scientific literature. Land is consistently referred to as an ‘inventor’ thus demeaning any ‘science’ that may be associated with his experiments and ideas. I have studied most of Land’s published work and it is characterized by a rarely seen straightforward logic and lucidity (as to description of methods used and results obtained).. truly a hallmark of the scientific method! The work of one other scientist comes to mind in this regard, the writings of the physicist David Bohm.
A device commonly tossed off to demean Land’s work is that ‘most aspects of his demonstrations were already well known’. This is a common thread seen most notably in a paper, to which I was referred by one purporting to speak for ‘vision science’, with the curious title ‘Land! Land!’ (I’ll not even provide the reference as I do not view the paper as in any way to be objective science). This method of obfuscation seems to have existed even in antiquity as noted in the quote that I use from da Vinci:

“Anyone who conducts an argument by appealing to authority is not using his intelligence; he is just using his memory.”
Leonardo da Vinci

No attempt is made to come to grips with, and actually explain, Land’s anomalous color vision experiments and results that began in 1955 and proceeded until Land’s death. Simply saying that these experiments had been ‘done before’ implies that they need no explanation. But they do!

And now there is an explanation – in the geometric view of light interaction with the retina.

I suggest that anyone interested in color vision actually read Land’s original papers. I obtained a compendium of these from the Rowland Institute in Cambridge, MA (originally founded by Land and now subsumed into Harvard University). A Ms. Holley Perry of that Institute was very kind in sending these to me. I do not know if they are still available but any serious student of vision should try to obtain them. Also instructive is viewing a documentary film made by the BBC in 1988 (‘Colourful Notions’). This film dwells on the subject of the riddle of color constancy in vision and includes a segment where Dr. Land personally demonstrates the essence of his color vision experiments.

GCH

Reading “The Purkinje rod-cone shift as a function of luminance and retinal eccentricity” by Anstis (Vision Research, 42, (2002), 2485-2492).

The effect defined from the paper’s abstract: “In the Purkinje shift, the dark adapted eye becomes more sensitive to blue than red as the retinal rods take over from the cones”

And further on from Results and Discussion: “In conclusion, the data plotted in Figs.3 and 5 show that the blue sensitivity increases as a joint function of increasing eccentricity and of decreasing luminance (emphasis mine). Relative blue sensitivity increases linearly with eccentricity, which projects the stimulus on to a larger population of rods, and this effect is multiplied by dark adaptation, which increases the activity of this enlarged population of rods relative to cones. This increasing activity in larger numbers of rods leads to a progressive increase in blue sensitivity”.

But first, there is no mention in the paper of ‘blue-sensitive cones’…? Rather, the author points to an ‘increasing activity’ (whatever that may mean?) of rods as the cause of increased blue sensitivity. ?????

The science of vision gets itself into a greater and greater tangle of confusion!

I will explain. The retina beyond 20 degrees eccentricity is composed chiefly of rods and it is, according to my explanation, rod-rod appositions that are sensitive to short blue wavelengths (with the precise dimension between adjacent rods actually defining the short wavelength limit of visual response). Cone response is not involved.

I have proposed that the function of the total population of blue-sensitive peripheral rods acts (in parallel) as a wide angle ‘light meter’ controlling pupillary constriction and thus light entrance into the eye. The ‘increased activity’ cited by the author follows in this explanation from, under the condition of dark adaption (i.e., when the pupil is dilated), a larger area of blue-sensitive rod-rod appositions is illuminated.

In case I have left anything out…blue wavelengths are refracted by the body of the eye (or in obsolete terminology: ‘chromatically abberrated”) beyond the fovea to eccentricities of ~ 20 degrees. It is obvious that, to the extent that any ability is left to discern color in peripheral vision, the short wavlength limit (blue) will dominate.

I remind: the sensation that we term ‘color’ is determined by ratioing intensities of wavelengths refracted to either side of the ‘pure green’ or ‘Land’ point at 7-8 degrees of retina eccentricity. It is obvious that this sensation will diminish at the larger retina angles of peripheral vision exactly as has been found.

THE PURKINJE SHIFT AND THE RESULTS REPORTED IN THIS PAPER ARE COMPLETELY EXPLAINED BY THE GEOMETRIC MODEL FOR LIGHT INTERACTION WITH THE RETINA.

I will be writing shortly more of my thoughts about the work of Edwin Land.

GCH