To study the circuits underlying color vision near the fovea, we developed a system with adaptive optics and high-speed eye tracking that enables tracking, targeting and stimulation of cones in living eyes. In two subjects with classified mosaics, cones stimulated with 543 nm light against a white background yield expected and unexpected percepts. Stimulated M cones yield either green or achromatic percepts, and the individual responses are pure – largely falling into color or achromatic reporting classes. L cones respond similarly, except the fraction of color-reporting cones yield red percepts. Similar results are found against a blue background, but the M cones convey distinctly blue percepts rather than green. What is unexpected is that the arrangement of the color and achromatic reporting cones are distributed in a way that is inconsistent with simple chromatically-opponent, center-surround midget ganglion cells. To understand how lateral interactions influence these percepts, we’re measuring cone sensitivity thresholds against different adapting background conditions. Collectively, these studies shed light on how foveal cone signals are transformed by retinal circuitry. 

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