An Ishihara-style test of animal colour vision

Abstract

Colour vision mediates ecologically relevant tasks for many animals, such as mate choice, foraging and predator avoidance. However, our understanding of animal colour perception is largely derived from human psychophysics, and behavioural tests of non-human animals are required to understand how colour signals are perceived. Here, we introduce a novel test of colour vision in animals inspired by the Ishihara colour charts, which are widely used to identify human colour deficiencies. In our method, distractor dots have a fixed chromaticity (hue and saturation) but vary in luminance. Animals can be trained to find single target dots that differ from distractor dots in chromaticity. We provide MATLAB code for creating these stimuli, which can be modified for use with different animals. We demonstrate the success of this method with triggerfish, Rhinecanthus aculeatus, which quickly learnt to select target dots that differed from distractor dots, and highlight behavioural parameters that can be measured, including success of finding the target dot, time to detection and error rate. We calculated discrimination thresholds by testing whether target colours that were of increasing colour distances (ΔS) from distractor dots could be detected, and calculated discrimination thresholds in different directions of colour space. At least for some colours, thresholds indicated better discrimination than expected from the receptor noise limited (RNL) model assuming 5% Weber fraction for the long-wavelength cone. This methodology could be used with other animals to address questions such as luminance thresholds, sensory bias, effects of sensory noise, colour categorization and saliency.

Seeing the rainbow: mechanisms underlying spectral sensitivity in teleost fishes

“…A number of behavioral studies have quantified the ability of fishes to discriminate colors by quantifying photoreceptor performance (i.e. receptor limited noise) in order to predict how well fish can perform particular discrimination tasks of ideal colored targets (Champ et al, 2016;Cheney et al, 2019;Pignatelli et al, 2010). However, here we focus on more biological, animal-centered tasks, such as foraging for prey or choosing mates.…”

Investigating Defensive Colouration in Nudibranch Molluscs using a Novel Analytical Framework for the Study of Animal Colour Patterns​​​​​​​

“…coinciding contrast (Lotto & Purves, 2000), retinex theory (E. H. Land, 1986)), threshold adjustments based on behavioural evidence (e.g. Cheney et al, 2019) and eye tracking weighted generation of transition matrices. Or, on the extreme end, the introduction of entirely novel capacities able to investigate aspects of visual perception, such as algorithms for the modelling of object and shape recognition beyond the level of the 'primal sketch' (Marr, 2010), thus capable of investigating higher level perceptual aspects of complex visual signals, such as more definite answers on the perception of shapes and elements in colour pattern elements, which in turn would allow for a more informed analysis of the perceptual importance of symmetry (Osorio, 1996;Forsman & Herretröm, 2004;Wagemans et al, 2012).…”

“…This was chosen over a traditional pairwise choice contrast (e.g. Goldsmith & Butler, 2003;Olsson, Lind, & Kelber, 2015) to simulate a level of complexity found in nature and allow simultaneous testing of multiple target stimuli without re-training (Cheney et al, 2019). The four choices were displayed against a noisy background (Fig.…”

“…Photoreceptor stimulation was calculated using spectral sensitivities of triggerfish from . Measures of photoreceptor noise are not available in this species, therefore we assumed a cone ratio of 1:2:2 (SW:MW:LW) with a standard deviation of cone noise (univariant Weber fraction) of 0.05 as per (Champ et al, 2016;Cheney et al, 2019). The cone abundance was normalised relative to the LW cone, which resulted in channel noise levels of 0.07:0.05:0.05 (SW:MW:LW).…”

“…The visual system of R. aculeatus has been used in a range of studies to model the visual perception of animal colouration or visual stimuli (e.g. Cheney et al, 2019;Green, Urquhart, van den Berg, Marshall, & Cheney, 2018) This chapter fulfils a broader purpose than just putting a number to the threshold entered into QCPA. It identifies a larger and more important issue that extends beyond the modality of luminance contrast perception.…”