Perception of visual texture, and the expression of disruptive camouflage by the cuttlefish, Sepia officinalis

Juvenile cuttlefish (Sepia officinalis) camouflage themselves by changing their body pattern according to the background. This behaviour can be used to investigate visual perception in these molluscs, and may also give insight into camouflage design. Edge detection is an important aspect of vision, and here we compare the body patterns that cuttlefish produced in response to checkerboard backgrounds with responses to backgrounds that have the same spatial frequency power spectrum as the checkerboards, but randomised spatial phase. For humans, phase randomization removes visual edges. To describe the cuttlefish body patterns we scored the level of expression of 20 separate pattern components, and then derived principal-components (PCs) from these scores. After varimax rotation, the first component (PC1) corresponded closely to the so-called disruptive body-pattern, and the second (PC2) to the mottle pattern. PC1 was predominantly expressed on checkerboards, and PC2 on phase randomised backgrounds. Thus cuttlefish probably have edge detectors that control expression of the disruptive pattern. Although the experiments used unnatural backgrounds it seems likely that cuttlefish display disruptive camouflage when there are edges in the visual background caused by discrete objects such as pebbles. We discuss the implications of these findings for our understanding of disruptive camouflage.