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.
191. Colour vision mediates ecologically relevant tasks for many animals, such as mate choice, 20 foraging and predator avoidance. However, our understanding of animal colour perception is 21 largely derived from human psychophysics, even though animal visual systems differ from 22 our own. Behavioural tests of non-human animals are required to understand how colour 23 signals are perceived by them. 24 2. Here we introduce a novel test of colour vision in animals inspired by the Ishihara colour 25 charts, which are widely used to identify human colour deficiencies. These charts consist of 26 dots that vary in colour, brightness and size, and are designed so that a numeral or letter is 27 distinguishable from distractor dots for humans with normal colour vision. In our method, 28 distractor dots have a fixed chromaticity (hue and saturation) but vary in luminance. Animals 29 can be trained to find single target dots that differ from distractor dots in chromaticity. We 30 provide Matlab code for creating these stimuli, which can be modified for use with different 31 animals. 32 3. We demonstrate the success of this method with triggerfish, Rhinecanthus aculeatus, and 33 highlight behavioural parameters that can be measured, including success of finding the 34 target dot, time to detect dot and error rate. Triggerfish quickly learnt to select target dots that 35 differed from distractors dots regardless of the particular hue or saturation, and proved to use 36 acute colour vision. We measured discrimination thresholds by testing the detection of target 37 colours that were of increasing colour distances (∆S) from distractor dots in different 38 directions of colour space. At least for some colours, thresholds indicated better 39 discrimination than expected from the Receptor Noise Limited (RNL) model assuming 5% 40Weber fraction for the long-wavelength cone. 41 4. This methodology seems to be highly effective because it resembles natural foraging 42 behavior for the triggerfish and may well be adaptable to a range of other animals, including 43 mammals, birds, bees and freshwater fish. Other questions may be addressed using this 44 methodology, including luminance thresholds, sensory bias, effects of sensory noise in 45 detection tasks, colour categorization and saliency. 46 47
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