Gordon G. Heath

Contour Interaction and Visual Resolution: Contralateral Effects

Detection of the gap in a four-position Landolt C presented to one eye is impaired by critically spaced surrounding bars seen only by the other eye. The intensity and spatial extent of this contralateral contour interaction match those obtained ipsilaterally. These results indicate that the neural site for this loss of visual information is supraretinal.

Flicker effects of receptor directional sensitivity.

&NA; When a Maxwellian‐view test field is alternately presented through different small areas in the pupil, a residual flicker is observed even though the luminance of the field is adjusted to compensate for the Stiles‐Crawford effect. The stimulus alternation frequency that eliminated this residual flicker was used to estimate the magnitude of modulation in the receptors resulting from the difference in direction of illumination. These results support the concept that directional sensitivity of cones is much more acute than the directional sensitivity represented by conventional measures of the Stiles‐Crawford effect.

TYPICAL TOTAL COLOR BLINDNESS REINTERPRETED: (Conclusion)

The bipartite dark-adaptation curve is not a >>symptom(( of typical achromasy, in the clinical sense. Still, it demands explanation, by any theory, just as loudly as does any of the characteristics already known a century ago. Sloan’s i 1954) impressive roundup of cases will convince anyone that the ,)kinked<( curve is a regular (though not unvarying) feature of the disease. It is not a freakish finding, as niight be thought if Lewis and Mandelbaum’s (1943) affected sibship still stood alone in the experimental literature. The original pure-rod theory was unable to cope with the demonstration that a majority of cases exhibit an Arago phenenienon. The original day-rod theory was, as we have noted, iion Kries’s way out. The idea of day rods ne>er had strong appeal, and became so well forgotten that in 1838 Hecht wrote as if he thought that it was new with himself. Later writers have credited it to Hecht! The day-rod theory took on its greatest importance when Lezuis and Mandelbaum, and later Sloan, reported finding a bipartite dark-adaptation curve in a great majority of cases. Lewis and Mandelbaum obtained such curves in three of their four cases. Sloan has found the kink in peripheral curves from eleven out of fourteen subjects, and although one of these eleven (S. J . ) probably had no kink a t the fovea, one of the other three ( M . McC), who had shown no kink a t 6 O , probahly did have one a t the fovea. Sloan (1954) attributes the pre-kink portions of her curves