Different sensations from cones with the same photopigment.

We used adaptive optics to study color fluctuation in the appearance of tiny flashes of light. For five subjects, near threshold, monochromatic stimuli with full widths at half maximum of 1/3 arcmin were delivered throughout a patch of retina near 1 deg in which we also determined the locations of L, M, and S cones. Subjects reported a wide variety of color sensations, even for long-wavelength stimuli, and all subjects reported blue or purple sensations at wavelengths for which S cones are insensitive. Subjects with more L cones reported more red sensations, and those with more M cones tended to report more green sensations. White responses increased linearly with the asymmetry in L to M cone ratio. The diversity in the color response could not be completely explained by combined L and M cone excitation, implying that photoreceptors within the same class can elicit more than one color sensation.