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The origin of the apparent farsightedness as revealed by retinoscopy in smaller eyes was investigated by using monochromatic retinoscopy on wild rabbits. Our results indicate that a combination of long wavelength light and chromatic aberration of the subject's dioptrics is the major source of this artifact.
The time course of recovery from chromatic adaptation in human vision was tracked by determining the wavelength of light that appears uniquely yellow (neither red nor green) both before and after exposure to yellowish green and yellowish red adapting lights. Recovery is complete within 5 min after steady light exposure. After exposure to the alternating repeated sequence 10-sec light/10-sec dark, the initial magnitude of the aftereffect is reduced but recovery is retarded. The results are interpreted in terms of two processes located at different levels in the hierarchical organization of the visual system. One is a change in the balance of cone receptor sensitivities; the second is a shift in the equilibrium baseline between opposite-signed responses of the red/green channel at the opponent-process neural level. The baseline-shift mechanism is effective in the condition in which repeated input signals originating at the receptors are of sufficient strength to activate the system effectively. Hence, this process is revealed in the alternating adaptation condition when the receptors undergo partial recovery after each light exposure, but receptor adaptation during continued steady light exposure effectively protects the subsequent neural systems from continued strong activation.
Two-pulse discrimination thresholds determined for homochromatic pulses presented as luminance increments or decrements are invariant with wavelength. Wavelength does affect two-pulse temporal resolution if chromatic pulses are presented in hue substitution, matched in luminance (with flicker photometry) to an achromatic background field. For relatively long pulses, the wavelength effect resembles trichromatic saturation discrimination, with poorest temporal resolution at 570 nm. For shorter pulses, temporal resolution for hue substitution stimuli appears related to saturation discrimination under conditions of artificial tritanopia. Under conditions of hue substitution, short-wavelength pulses yield good temporal resolution.
In a space where Cartesian coordinates represent the excitations of the three cone types involved in color vision, a plane of constant luminance provides a chromaticity diagram in which excitation of each cone type (at constant luminance) is represented by a linear scale (horizontal or vertical), and in which the center-of-gravity rule applies with weights proportional to luminance.
Monochromatic targets presented at 30 degrees excentricity on orange, magenta and blue backgrouds are used. A small monochromatic light, 476 nm on orange, 551 nm on magenta and 621 nm on blue, is flashed at 3 cps-1 on the centre of the targets. The size of the targets is varied and their luminance adjusted using neutral filters until the flashing light is just not visible. This method allows the study of chromatic mechanism sensitivity and of retinal interactions (summation and inhibition). Some observations in normal as well as in pathological conditions are presented.
A simple method is proposed and analysed which explains characteristic manifestation of the enchancement effect (2nd Emerson effect) and of chromatic transients effect (Blinks effect). The model is based on the hypothesis concerning the ATP/NADP concentrations ratio with a change of falling light wavelength. The model is suggested to reflect the behaviour of the reduction pentosophosphate cycle (Calvin cycle) under low illumination intensity, when the photosynthesis rate is determined only by ATP and NADP.H concentrations formed in the course of different photochemical reactions.
Platelets from the rabbit and rat, respectively, were incubated with sodium 51Cr-chromate and 3H-diisopropylfluorophosphate (3H-DFP) in the same manner as for platelet survival studies. A third isotope, 125I, was incorporated into a labeled antibody raised against a partially purified pig platelet membrane fraction. The 51Cr label was found to be concentrated predominantly in the cytoplasm, with a marked degree of association with mitochondria, whereas the tritium label appeared to be largely confined to the periphery of the platelet, particularly in association with the open canalicular system. The 125I-labeled antibody showed a very marked association with the plasma membrane and the open canalicular system, suggesting a membrane-bound affinity.
We have modified the original Goldmann perimeter by replacing the source and shutter by a Xenon arc source with maximum target luminance of 3183 cdm-2, and a quartz iodine lamp yielding maximum background luminance of 150 cdm-2, both measured at the bowl. Colorimetric and spectrophotometric specifications of the new colour targets are comparable to the original, but give luminance intensities equivalent to 318 cdm-2: levels only realized for the white target in the original system. Chromatic profiles are comparable to previous profiles for achromatic targets and the close correspondence between the retinal threshold gradients produced by the two methods simplifies comparison of data obtained with out instrument with those obtained from routine static perimetry. Under high luminance conditions we do not find the relative foveal scotoma for blue targets observed by other researchers. The use of photometrically equated targets well withi; the photopic levels is an improvement on present methods of colour perimetry.
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