Does conspicuousness scale linearly with colour distance? A test using reef fish

Santiago, Carl, Green, Naomi F, Hamilton, Nadia, Endler, John A, Osorio, Daniel C, Marshall, N Justin and Cheney, Karen L 2020, Does conspicuousness scale linearly with colour distance? A test using reef fish, Proceedings of the Royal Society B: biological sciences, vol. 287, no. 1935, pp. 1-8, doi: 10.1098/rspb.2020.1456.

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Title Does conspicuousness scale linearly with colour distance? A test using reef fish
Author(s) Santiago, Carl
Green, Naomi F
Hamilton, Nadia
Endler, John AORCID iD for Endler, John A
Osorio, Daniel C
Marshall, N Justin
Cheney, Karen L
Journal name Proceedings of the Royal Society B: biological sciences
Volume number 287
Issue number 1935
Article ID 20201456
Start page 1
End page 8
Total pages 8
Publisher Royal Society
Place of publication London, Eng.
Publication date 2020-09-30
ISSN 0962-8452
Keyword(s) Biology
colour measurement
colour vision assessment
Environmental Sciences & Ecology
Evolutionary Biology
Life Sciences & Biomedicine
receptor noise limited model
Science & Technology
visual ecology
Summary To be effective, animal colour signals must attract attention—and therefore need to be conspicuous. To understand the signal function, it is useful to evaluate their conspicuousness to relevant viewers under various environmental conditions, including when visual scenes are cluttered by objects of varying colour. A widely used metric of colour difference (ΔS) is based on the receptor noise limited (RNL) model, which was originally proposed to determine when two similar colours appear different from one another, termed the discrimination threshold (or just noticeable difference). Estimates of the perceptual distances between colours that exceed this threshold—termed ‘suprathreshold’ colour differences—often assume that a colour's conspicuousness scales linearly with colour distance, and that this scale is independent of the direction in colour space. Currently, there is little behavioural evidence to support these assumptions. This study evaluated the relationship between ΔS and conspicuousness in suprathreshold colours using an Ishihara-style test with a coral reef fish, Rhinecanthus aculeatus. As our measure of conspicuousness, we tested whether fish, when presented with two colourful targets, preferred to peck at the one with a greater ΔS from the average distractor colour. We found the relationship between ΔS and conspicuousness followed­­ a sigmoidal function, with high ΔS colours perceived as equally conspicuous. We found that the relationship between ΔS and conspicuousness varied across colour space (i.e. for different hues). The sigmoidal detectability curve was little affected by colour variation in the background or when colour distance was calculated using a model that does not incorporate receptor noise. These results suggest that the RNL model may provide accurate estimates for perceptual distance for small suprathreshold distance colours, even in complex viewing environments, but must be used with caution with perceptual distances exceeding­ ­10 ΔS.
Language eng
DOI 10.1098/rspb.2020.1456
Indigenous content off
Field of Research 06 Biological Sciences
07 Agricultural and Veterinary Sciences
11 Medical and Health Sciences
HERDC Research category C1 Refereed article in a scholarly journal
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