Color appearance of filled-in backgrounds affects hue cancellation, but not detection thresholds.

A long-wavelength background can affect the appearance of an increment of light superimposed upon it in two ways. It can change the visual system's sensitivity to the increment, and it can change the appearance of the increment by directly adding redness to it. Through selective retinal-image stabilization, we evoked the filling-in phenomenon to change the appearance of 640- and 575-nm backgrounds. Either of these backgrounds could be made to appear red or yellow, depending upon whether it was viewed under stabilized or unstabilized conditions. When the appearance of the 640-nm background was altered by filling-in to appear less red, test probes superimposed upon it required less 540-nm component to achieve an equilibrium hue. Increment thresholds measured on the 640- and 575-nm backgrounds, however, did not change with the appearance of the backgrounds.

Molecular genetics of inherited variation in human color vision.

The hypothesis that red-green "color blindness" is caused by alterations in the genes encoding red and green visual pigments has been tested and shown to be correct. Genomic DNA's from 25 males with various red-green color vision deficiencies were analyzed by Southern blot hybridization with the cloned red and green pigment genes as probes. The observed genotypes appear to result from unequal recombination or gene conversion (or both). Together with chromosome mapping experiments, these data identify each of the cloned human visual pigment genes.

Stereo hysteresis revisited.

I have replicated the historic Fender and Julesz stereo hysteresis study [J. opt. Soc. Am. 57, 819-830 (1967)] but with a different method of image stabilization. My results generally support their findings that once fused, the two stabilized monocular images of a random-dot stereogram can be separated on the retinas by as much as 2 deg and still remain fused. However, there is one major exception: whereas they found it necessary to realign the images to within 6 min of arc for refusion to occur, I find that refusion of stabilized random-dot stereograms may occur well outside the classical Panum's fusional area.

Noninvasive intracranial pressure monitoring.

Because skull elasticity has been demonstrated (through holographic interferometry), the assumption was made that even a small change in intracranial hydrostatic pressure might change the bitemporal diameter of the skull measurably. The authors devised a relatively noninvasive instrument for measuring skull diameter changes with changing intracranial pressure and evaluated its performance in cadavers and dogs, with encouraging results. With this method of measuring intracranial pressure, changes in pressure of as little as 2 mm Hg can be detected. The method measures relative rather than absolute pressure; it is postulated that this shortcoming can be overcome through further effort.

Temporal modulation sensitivity of the blue mechanism: measurements made with extraretinal chromatic adaptation.

Using the counterphase-modulated-tritan-metamers method of Wisowaty and Boynton [Vision Res. 20, 895-909 (1980)], we measured the modulation sensitivity function of the blue mechanism on dark backgrounds and on uniform yellow backgrounds that were produced either by illuminating the retina with yellow light or by filling-in of a stabilized retinal image. When measured on yellow backgrounds, temporal modulation sensitivity was markedly reduced whether the background was produced by retinal illumination or by filling-in. This sensitivity reduction has been attributed by other researchers to changes in the transmission characteristics of the blue/yellow pathway caused by yellow adaptation. Our results obtained with backgrounds that appeared yellow due to filling-in indicate that the site of adaptation must be extraretinal as there was no yellow light reaching the retina in the vicinity of the test probe.

On seeing reddish green and yellowish blue.

Four color names-red, yellow, green, and blue-can be used singly or combined in pairs to describe all other colors. Orange, for example, can be described as a reddish yellow, cyan as a bluish green, and purple as a reddish blue. Some dyadic color names (such as reddish green and bluish yellow) describe colors that are not normally realizable. By stabilizing the retinal image of the boundary between a pair of red and green stripes (or a pair of yellow and blue stripes) but not their outer edges, however, the entire region can be perceived simultaneously as both red and green (or yellow and blue).

Psychophysical evidence for more than two kinds of cone in dichromatic color blindness.

Psychophysical evidence shows that at least some classically diagnosed dichromats have three cone types rather than two. The anomalous cones, previously thought to be absent, are less sensitive than normal cones to both spectral and temporal variations, and have spectral sensitivities like those of the abnormal cones of anomalous trichromats. These results are not consistent with either loss or replacement models of X-linked recessive color-vision defects, since some dichromats apparently have the same three photopigments as anomalous trichromats.

The Roth 28-hue test.

The Roth 28-hue test, first described in 1966, uses every third color cap from the Farnsworth-Munsell 100-hue (85-color-cap) test. Protans, deutans, and tritans exhibit slightly different confusion axes on the Roth 28-hue test and the Farnsworth D-15 test. These axes are illustrated on a CIE chromaticity diagram. The little-used Roth 28-hue test may be a good compromise between the D-15 and 100-hue tests, but clinical trials for verification are needed.