PubMed · 14771865
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N R BARTLETT. 1950. Vision.. https://doi.org/10.1146/annurev.ps.01.020150.000335
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We evaluated orientation discrimination in color and luminance vision using an external noise paradigm. Stimuli were spatiotemporal patches of 2D orientation noise isolating the achromatic, red-green and blue-yellow mechanisms, and matched in multiples of contrast detection threshold. We found a monotonic increase of orientation discrimination thresholds with the stimuli orientation bandwidths that is similar for both color and luminance contrasts. This dependence was fitted with two suitable models. A variance summation model suggests that internal orientation noise is significantly greater for the chromatic than for the achromatic mechanisms, while the efficiencies are similar. A gain control model of orientation tuning suggests that both chromatic and achromatic mechanisms are characterized by broadly tuned orientation detectors and that the relative chromatic deficit in orientation discrimination may only result from a slightly broader orientation tuning for the chromatic mechanisms. The moderate deficiency in chromatic orientation discrimination may account for the small differences found in shape perception between color and luminance vision.
This study provides evidence for the existence of a low-level chromatic motion mechanism and further elucidates the conditions under which its operation becomes measurable in an experimental stimulus. Observers discriminated the direction of motion of amplitude modulated (AM) gratings that were defined by luminance or chromatic variation and masked with spatiotemporally broadband luminance or chromatic noise. The size and retinal location of the stimuli were varied and the effects of broadband noise and grating masks were both compared with the cohort of stimuli. Some significant disparities in the published literature were well explained by the results. In conclusion, evidence for a chromatically sensitive motion mechanism that evades the, detrimental effects of a luminance mask was found only at the fovea and only when the stimulus was small and centrally placed.
BACKGROUND: An analysis of the wavefront in human eyes has yielded new findings with respect to the cones and other elements of the retina. But the correction of higher-order wavefront aberrations in photorefractive processes is still associated with basic difficulties. MATERIALS AND METHODS: The world literature relating to wavefront corrections in experimental research and the correction of photorefractive aberrations in the human eye is surveyed. RESULTS AND CONCLUSIONS: The correction of higher-order aberrations has permitted a vast improvement in the resolution of the cone-pattern picture existing in vivo. As a consequence, new findings with regard to colour physiology have been forthcoming. On the other hand, the application of wavefront corrections in photorefractive procedures has been only partially successful.