Dark scene elements strongly influence cuttlefish camouflage responses in visually cluttered environments

Abstract

This study investigated how cuttlefish (Sepia officinalis) camouflage patterns are influenced by the proportions of different gray-scales present in visually cluttered environments. All experimental substrates comprised spatially random arrays of texture elements (texels) of five gray-scales: Black, Dark gray, Gray, Light gray, and White. The substrates in Experiment 1 were densely packed arrays of square texels that varied over 4 sizes in different conditions. Experiment 2 used substrates in which texels were disks separated on a homogeneous background that was Black, Gray or White in different conditions. In a given condition, the histogram of texel gray-scales was varied across different substrates. For each of 16 cuttlefish pattern response statistics c, the resulting data were used to determine the strength with which variations in the proportions of different gray-scales influenced c. The main finding is that darker-than-average texels (i.e., texels of negative contrast polarity) predominate in controlling cuttlefish pattern responses in the context of cluttered substrates. In Experiment 1, for example, substrates of all four texel-sizes, activation of the cuttlefish “white square” and “white head bar” (two highly salient skin components) is strongly influenced by variations in the proportions of Black and Dark gray (but not Gray, Light gray, or White) texels. It is hypothesized that in the context of high-variance visual input characteristic of cluttered substrates in the cuttlefish natural habitat, elements of negative contrast polarity reliably signal the presence of edges produced by overlapping objects, in the presence of which disruptive pattern responses are likely to achieve effective camouflage.