WAVELENGTH VARIATION OF THE DIRECTIONAL SENSITIVITY OF THE STILES PI-1 (MU)

The variation of the directional sensitivity of Stiles' (1953) π1(μ) mechanism was measured throughout the spectrum on one deuteranope. For wavelengths greater than about 550 nm, the directional properties measured for π1(μ) are nearly identical to those for this deuteranope's π5(μ) mechanism. This supports the hypothesis of Pugh (1976) that π1(μ) is a composite mechanism so that in the yellow-red part of the spectrum its sensitivity is determined by long- (and/or medium-) wave sensitive cones. It also obviates the contradiction between the single π1(μ) directional sensitivity result of Stiles (1939) and the suggestion (Enoch and Stiles, 1961) that short-wave sensitive cones are more sensitive to light entering through the edge than through the center of the pupil. This deuteranope's long-wave sensitive cones appear to be most sensitive to backgrounds entering the eye 0.5 mm nasal, to the center of his pupil while his short-wave sensitive cones appear to be most sensitive to light entering 0.2 mm temporal to the center of the pupil. Differences in the estimate of losses in the lens below 450 nm in the spectrum are too large to exclude either self-screening or the Snyder-Pask waveguide theories as applied to this subject's short-wave sensitive cones. © 1979.