Exploiting colour space geometry for visual stimulus design across animals

Abstract

Colour vision represents a vital aspect of perception that ultimately enables a wide variety of species to thrive in the natural world. However, unified methods for constructing chromatic visual stimuli in a laboratory setting are lacking. Here, we present stimulus design methods and an accompanying programming package to efficiently probe the colour space of any species in which the photoreceptor spectral sensitivities are known. Our hardware-agnostic approach incorporates photoreceptor models within the framework of the principle of univariance. This enables experimenters to identify the most effective way to combine multiple light sources to create desired distributions of light, and thus easily construct relevant stimuli for mapping the colour space of an organism. We include methodology to handle uncertainty of photoreceptor spectral sensitivity as well as to optimally reconstruct hyperspectral images given recent hardware advances. Our methods support broad applications in colour vision science and provide a framework for uniform stimulus designs across experimental systems. This article is part of the theme issue ‘Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods’.

A chromatic feature detector in the retina signals visual context changes

“…To ensure proper chromatic scaling between the different experimental apparatuses with different spectral profiles, we described the relative activation of M- and S-cones by the green and UV LEDs in the stimulation setup used in the two photon imaging experiments (setup A) by a matrix and the relative activation of M-and S-cones by the stimulation setup used in the patch-clamp experiments (setup B) by a matrix where diagonal entries describe the activation of M-cones by the green LED, and of S-cones by the UV LED, and entries in the off-diagonal describe the cross-activation (i.e., M-cones by UV-LED and S-cones by green LED). The activation of M-cones and S-cones e T = ( e m , e s ) by a stimulus x ∈ ℛ 2 × 1 displayed on a given stimulation setup was approximated as e = A x (82). Hence, a stimulus x I displayed on setup B, defined as x I = B −1 A x , will achieve the same photoreceptor activation as stimulus x displayed on setup A.Since the solution exceeded the valid range of the stimulator ([0, 255]), we added an offset and multiplied with a scalar factor to ensure all stimuli were within the valid range.…”

Hue selectivity from recurrent circuitry inDrosophila

“…We chose dawn-like conditions, because this is when flies are most active (Lazopulo et al, 2019). We fit the LED intensities to the background light condition using methods described in Christenson et al (2022). background LED intensities are (in µE): 0.01 for dUV, 0.06 for for UV, 0.1 for violet, 0.25 for blue, 0.33 for green, and 0.25 for orange.…”

“…We obtained the LED intensities by first randomly sampling capture values in the fly color space around an overall relative capture of 5 (Fig. S6), and then fitting the target captures using methods previously described in Christenson et al (2022). For each imaging session, we flashed a subset of this stimulus set (approx.…”

“…The stimuli we used are characterized by computed photon activations for the four fly opsins, labelled by µ = 1, 2, 3, 4, and given by X µ = log ((q µ + 0.001)/1.001), with q µ the calculated relative capture for opsin µ, as described previously in Heath et al (2020); Christenson et al (2022). We decompose the components of the 4-dimensional vector X into a 3-dimensional vector ⃗ x lying within the color tetrahedron and a scalar l that is the projection of X along the axis connecting the zero point in the full color space to the white point in the color tetrahedron.…”

High diversity of arthropod colour vision: from genes to ecology

“…If the photoreceptor sensitivities are known, behavioural methods, such as described by Cheney et al [125], Christenson et al . [126], Hempel de Ibarra et al . [99] and Werner [94], allow experimenters to design visual stimuli that are well suited to map the colour space of a species and allow for a better understanding of their perceptual colour worlds.…”