Abstract
We studied the colors reported by subjects in response to stimulation of individual cones. We targeted cones, whose spectral type was previously identified, with AO-corrected flashes of light (543 nm) and the subjects indicated the color of the flash. Cones were targeted on both white and blue backgrounds. Reports from repeated stimulation of single cones were consistent, but were not predicted by the spectral sensitivity of the stimulated cone alone. Both the background and the local neighborhood of the cone influenced the sensation reported. On a white background, the majority of L and M cones (N=221) were dominated by white responses (71%), while a small group of cones elicited red (19%) and green (10%) percepts. Contrary to classical theories, L or M cones surrounded by neighbors of opposing spectral class generated white percepts, not red or green. Against a blue background (N=181) most cones again mediated white (72%) responses and the remainder reliably signaled red (11%) or blue (18%). Across background conditions cones associated with white and red percepts tended to maintain the same behavior, whereas green signaling cones switched to blue. In a subset of cones, the intensity of the stimulus was varied, but color naming behavior did not differ. Together, our results were consistent with the idea that the brain associates elementary color and achromatic sensations with the output of a group of opponent neurons – separate from foveal L–M midget ganglion cells – early in the visual pathway.