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

To be effective, animal colour signals must attract attention – and therefore need to be conspicuous. To understand 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 JND, just noticeable difference). Estimates of the perceptual distances between colours that exceed this threshold – termed ‘suprathreshold’ colour differences – often assumes that a colour’s conspicuousness scales linearly with colour distance, and that this scale is independent of direction in colour space. Currently, there is little behavioural evidence to support these assumptions. This study evaluated the relationship between ΔS and cons...