A five‐channel LED display to investigate UV perception

Abstract

1. The ability to see ultraviolet (UV) light (<400 nm) may have importance for foraging, communication or navigation in many taxa including insects, crustaceans, fishes, amphibians, reptiles, birds and mammals. Behavioural experiments reveal how vision mediates such behaviour; however, our knowledge of UV perception is constrained by the challenge of creating and calibrating stimuli that reflect or emit UV. Commonly used technologies for displaying visual stimuli-such as computer screens and printers-are designed for human vision and thus are unsuitable for testing UV perception. 2. To overcome this limitation, we designed and constructed a display with five spectral channels with peak wavelengths as follows: red at 629 nm, green at 526 nm, blue at 466 nm, violet at 395 nm and UV at 367 nm. Each pixel of the display consists of five LEDs with a baffle to prevent crosstalk from adjacent pixels and a diffuser to promote uniform colour mixing. The LEDs are driven by high-performance pulse-width-modulated constant-current drivers with a maximum flicker rate of 64 kHz and a maximum frame rate of 6.5 kHz. This method allows colour mixing with wavelengths as low as 350 nm to be calibrated and tested rapidly and concurrently. 3. To demonstrate the utility of this display, we conducted colour detection tests using the anemonefish, Amphiprion ocellaris, a species known to have UV-sensitive cones. Fish were able to associate pecking all target colours ('Blue', 'UV-grey' and 'UV') with a food reward, demonstrating for the first time, UV perception in A. ocellaris. 4. The RGB-V-UV LED display is a useful device for behavioural tests of colour vision across a broad spectrum (350-650 nm) visible to many animals and can be used to investigate various questions concerning animal perception, including colour discrimination and categorisation. We include design documents and source code so this system can be further developed and modified to investigate other visual behaviours in a variety of taxa. K E Y W O R D S animal behaviour, colour vision, coral reefs, ultraviolet vision, visual ecology This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Anemonefish have finer color discrimination in the ultraviolet

“…This advance was made possible by our five channel LED display customized to anemonefish vision (Fig 2B). The display also allowed us to show that anemonefish can discriminate a wide variety of non-spectral colors from grey, which would be highly difficult with monochromatic test lights ( 15, 27 ).…”

“…Many animals have ultraviolet (UV) sensitive (<400 nm) photoreceptors [reviewed by (1, 2)], and UV-vision contributes to behaviours including foraging (3, 4), celestial navigation (5, 6), mate selection (7–11), individual recognition (12), and aggressive displays (13, 14). But partly due to the technical challenge of producing UV-stimuli (15), few studies have tested its contribution to color discrimination, and it is unclear how UV sensitivity compares to that of visible range photoreceptors.…”

“…To do this, we used nine different sets of test colors produced by a five-channel (RGB-V-UV) LED display (15) customized to the A. ocellaris visual system. The contribution of photoreceptors to color vision were evaluated by the Receptor Noise Limited (RNL) model (19), which fits the psychophysical data of many species by assuming that color discrimination is set by chromatic opponent mechanisms whose performance is limited by noise arising in the photoreceptors (39, 40).…”

Color in motion: Generating 3-dimensional multispectral models to study dynamic visual signals in animals

“…This is a real limitation for animals-like birds-with a wider range of wavelength sensitivity. However, technology is improving for creating birdvisible colors with LEDs and perhaps more sophisticated screens will be available in the future (Stoddard et al, 2020;Powell et al, 2021).…”

Exploiting colour space geometry for visual stimulus design across animals

“…Our method can directly be applied to LCD screens and any other screens that pack small LEDs onto single pixels [38], as long as the set of light sources is adequate for the animal in question (see §3c). However, if the gamut afforded by the available set of LEDs used in a particular display is small, it will require a change in the LED set at every pixel , a time-consuming and expensive task.…”