The saturation of monochromatic lights obliquely incident on the retina.

Abstract

SUMMARY1. Foveal dark-adaptation undertaken to test the hypothesis that the excitation of rods causes the desaturation of 'yellow' lights in a 10 field traversing the margin of the pupil, fails to exclude that possibility.2. The desaturation is largest for a 1°outside diameter annular test, is still measurable with a 0.50 circular disk, but disappears for a 0.29°disk. The supersaturation of obliquely incident 501-2 nm test light follows the opposite pattern; it disappears with an annulus and is largest for a 0.290 circular field. It is unlikely that rods replace short-wave sensitive cones in the trichromatic match of an obliquely incident test with normally incident primaries.3. If rods as well as all three cones species are involved, the matches might not be trichromatic in the strong sense. Grassmann's law of scalar multiplication was tested and shown not to hold for the match of an obliquely incident test with normally incident primaries, though it remains valid whenever, both primaries and test strike the retina at the same angle of incidence (independent of that angle).4. The result in section 3 (above) cannot be due to rod intrusion. It persists (and becomes more conspicuous) on backgrounds (4 0 log scotopic td) which saturate rods. Moreover obliquely incident 'yellow' lights remain desaturated in intervals in the dark after a full bleach, whilst the test field is below rod threshold. The amount of desaturation does not differ appreciably from that normally found.5. The assumption of the unified theory of Alpern, Kitahara & Tamaki (1983) that the outer segments of only a single set of three cone species (with acceptance angles wide enough to include the entire exit pupil) contain the visual pigments absorbing both the normally incident primaries and the obliquely incident test is disproved by these results.6. Failure of Grassmann's law is most conspicuous under the conditions for which the changes in saturation upon changing from normal to oblique incidence are greatest and least when the saturation changes are the smallest.7. Either all unified theories of the Stiles-Crawford effects are wrong or all the

The dependence of the colour and brightness of a monochromatic light upon its angle of incidence on the retina.

“…That is a property the unified theory must attribute to short-wave cones and it is difficult indeed to reference authority for rejecting H3(u) as the most reasonable operational definition of their action spectrum. In the following paper (Alpern & Tamaki, 1983) this dilemma is examined in detail.…”

“…This last assumption is examined in the following paper (Alpern & Tamaki, 1983). This one describes a repetition of the Enoch & Stiles (1961) experiment on two more subjects, evaluating the generality of their matching data.…”