Fig. 1: S-cone-opponent influences into ipRGCs and selective stimuli to target these pathways.

a, The cone inputs to the melanopsin-containing ipRGCs in the human retina combine light information in an opponent, subtractive fashion, pitting signals from the S cones against signals a joint L- and M-cone signal encoding luminance (schematic diagram, simplifying the underlying anatomy; Mel = melanopsin-containing ipRGC, RHT = retinohypothalamic tract). b, The spectral sensitivities of the L, M and S cones have distinct peaks (λ_max) but are overlapping. c, The joint spectral sensitivity of the opponent −S + (L + M) channel, showing distinct wavelength regions yielding positive versus negative activations. d, Chromaticity diagram (CIE 1931 xy chromaticity) showing the chromaticity coordinates of the background condition (corresponds to colour temperature of 6,500 K daylight (D65)), the two modulation spectra and the daylight locus (daylight spectra between 4,000 K and 25,000 K). e, Overview of stimulus conditions and its contrast properties. Stimuli are unipolar sinusoidally flickering excursions from the background in the direction of the +S − (L + M) and −S + (L + M) poles of the blue–yellow channel. f, Spectral irradiance distribution of the constant background, keeping excitation constant for L, M and S cones and melanopsin. Inset: contrast for the L, M and S cones, and melanopsin for the modulation spectrum against the background spectrum. g, Spectral irradiance distribution of the +S − (L + M) stimulus, biasing S cones over luminance (blue solid line) against the background (dashed grey line). Inset: contrast for the L, M and S cones, and melanopsin for the modulation spectrum against the background spectrum. h, Spectral irradiance distribution of the −S + (L + M) stimulus, biasing S cones over luminance (blue solid line) against the background (dashed grey line). Inset: contrast for the L, M and S cones, and melanopsin for the modulation spectrum against the background spectrum.