Cuttlefish responses to visual orientation of substrates, water flow and a model of motion camouflage.

Low-level mechanisms in vertebrate vision are sensitive to line orientation. Here we investigate orientation sensitivity in the cuttlefish Sepia pharaonis, by allowing animals to settle on stripe patterns. When camouflaging themselves cuttlefish are known to be sensitive to image parameters such as contrast and spatial scale, but we find no effect of background orientation on the patterns displayed. It is nonetheless clear that the animals see orientation, because they prefer to rest with the body-axis perpendicular to the stripes. We consider three possible mechanisms to account for this behaviour. Firstly, that the body patterns are themselves oriented, and that the cuttlefish align themselves to aid static camouflage. This is unlikely, as the patterns displayed have no dominant orientation at any spatial scale. A second possibility is that motion camouflage favours alignment of the body orthogonal to background stripes, and we suggest how this alignment can minimise motion signals produced by occlusion. Thirdly we show that cuttlefish prefer to rest with their body-axis parallel to the water flow, and it is possible that they use visual patterns such as sand ripples to determine water flow.