WHO:	Heidi J. Hofer , PhD Defense
TOPIC:	Implications of the Trichromatic Mosaic for Color Vision
ABSTRACT:	The organization of the human trichromatic mosaic and its role in color vision is not well understood. The advent of adaptive optics for the human eye has made it possible to characterize the arrangement of the three classes of cone photoreceptors, which are responsible for color vision, in living human retinas. It is also now possible to deliver stimuli to the retinas of those same subjects that are smaller than the receptors responsible for their detection. This technology is exploited to uncover the influence of individual cones, and their distribution within The retina, on color perception by studying the appearance of tiny, brief, near-threshold stimuli, in subjects with known mosaics. The locations of L, M, and S cones within patches of retina at 1 degree eccentricity were determined in S color normal subjects. L:M ratio varied from 1:2.7 to 16.5:1, a much larger range than previously suggested. Despite the large variability, all subjects perceived hues in the same way. L and M cones were generally found to be randomly arranged. S cone arrangement was either random or slightly regular. Detection and appearance of punctate stimuli was studied in 5 of these subjects at the same retinal location. Color appearance varied systematically with L:M ratio. Contrary to initial expectations, subjects reported a large variety of percepts, even for extremely low probabilities of detection. For test wavelengths to which S cones are insensitive, subjects reported up to 27% of colored flashes blue. These blue responses varied with wavelength in a manner consistent with the sensitivity of M cones. White responses increased linearly with the asynunetry in L:M ratio, behavior generally inconsistent with the hypothesis that both L and M cones must be stimulated for white sensations to occur. These results confirm previous suggestions that M cones contribute to sensations of blueness. The variety of color percepts and the statistics of the blue and white responses are inconsistent with the assumption that color appearance depends solely on the photopigment in the receptors mediating detection. Instead, the results imply that individual cones of each class can generate different percepts. Ã
WHEN:	6/11/2003 11:00:00 AM
WHERE:	Meliora 269

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