The influence of colour and motion on signal visibility in the lizard Anolis cristatellus ABSTRACT: Anoline lizards communicate with displays consisting of motion patterns of a colourful throat fan called the dewlap. We used a visual motion-detection reflex as an assay to test the effects of stimulus/background colour and brightness contrast on the probability of detection of a moving coloured (i.e. dewlap-like) stimulus in Anolis cristatellus. We found that the probability of stimulus detection depended on two additive visual-system channels: one which responded to brightness contrast and one which responded to colour contrast independent of brightness. The brightness channel was influenced only by wavelengths longer than 450 nm, and probably received input only from middle and/or long wavelength cone photoreceptors. The colour contrast channel appeared to receive input from all four cone photoreceptor classes found in the anoline retina. We developed a multilinear regression equation which described, to a reasonable degree of accuracy, most of the results of this study. In the future this equation could be used to predict the relative visibility of different coloured stimuli in different habitat light conditions. This should be useful for testing ideas that relate habitat light conditions to the evolution of signal design.