Fig. 1: The Drosophila color space and experimental methods.
From: Hue selectivity from recurrent circuitry in Drosophila
a, Relative spectral sensitivity of opsins expressed in the fruit fly retina; data from ref. 48 fit with the equation from ref. 49. b, Fly color space defined by the photon captures q of Rh3, Rh4, Rh5 and Rh6 opsins. The luminance of a color is defined as the sum of opsin captures (∑iqi). c, Fly chromatic hyperplane defined by restricting the luminance to a constant value. In the chromatic hyperplane, there are four vertices, one for each opsin, six edges between pairs of opsins and four faces connecting three opsins. The gray box indicates the gamut of fly colors accurately reproducible with our stimulation system. Within the chromatic plane, the saturation of a color is defined as the distance of the stimulus from the fly’s effective white point (that is, the center of the tetrahedron). The hue of a color is defined by the angular direction of the color vector stretching from the white central point to a particular stimulus point. d, 2D projection of the fly color space onto the two color-opponent components: (Rh5 + Rh6) − (Rh3 + Rh4) and (Rh4 + Rh5) − (Rh3 + Rh6). e, Two-photon imaging setup. The fly is secured facing the LED setup, and LED sources are combined using a custom color mixer to form a single collimated full-field beam. D, deep UV; U, UV; V, violet; B, blue; L, lime; O, orange. f, Schematic of the fruit fly color circuit indicating the imaging fields used to record photoreceptors and interneurons in the medulla and Tm neurons in the lobula. g, Example dF/F traces of single regions of interest (ROIs; gray traces) in response to the neuron’s preferred stimulus. The black line indicates the mean response. a.u., arbitrary units.
