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 randomized 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-randomized backgrounds. Thus, cuttlefish probably have edge detectors that control the expression of disruptive pattern. Although the experiments used unnatural backgrounds, it seems probable 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.

SUMMARY Plaice (Pleuronectes platessa) is a flatfish well-known for the ability to vary its body pattern, probably for camouflage. This study investigates the repertoire of patterns used by juvenile plaice, by describing how they respond to shifts between three artificial backgrounds. Two basic patterns are under active control, fine `spots' and coarser `blotches'. These patterns are superimposed on a fairly uniform ground. For the six plaice studied, the levels of expression of the spot and blotch patterns varied continuously and independently according to the visual background, and in a manner consistent with their being cryptic. The repertoire of plaice appears to be intermediate between the tropical flatfish Bothus ocellatus,which has three separate basic patterns, and two temperate species Paralichthys lethostigma and Pseudopleuronectes americanus,which have one each. It is interesting to consider how mixing a small number of coloration patterns is effective for camouflage, and why the demands of this task may lead to differences between species.

SummaryCuttlefishes of the genus Sepia produce adaptive camouflage by regulating the expression of visual features such as spots and lines, and textures including stipples and stripes. They produce the appropriate pattern for a given environment by co-ordinated expression of about 40 of these 'chromatic components'. This behaviour has great flexibility, allowing the animals to produce a very large number of patterns, and hence gives unique access to cuttlefish visual perception. We have, for instance, tested their sensitivity to image parameters including spatial frequency, orientation and spatial phase. One can also ask what features in the visual environment elicit a given coloration pattern; here most work has been on the disruptive body pattern, which includes welldefined light and dark features. On 2-D backgrounds, isolated pale objects of a specific size, that have well-defined edges, elicit the disruptive pattern. Here we show that visual depth is also relevant. Naturally, cuttlefish probably use the disruptive pattern amongst discrete objects, such as pebbles. We suggest that they use several visual cues to 'identify' this type of background (including: edges, contrast, size, and real and pictorial depth). To conclude we argue that the visual strategy cuttlefish use to select camouflage is fundamentally similar to human object recognition.

Cuttlefish (Sepia officinalisLinnaeusCephalopods have a remarkable ability to change the color and pattern of their skin, and research has demonstrated that visual input regulates these changes. Cuttlefish skin can show 20 -50 chromatophore patterns that are used for both camouflage and communication (1). Cuttlefish can change their body patterns within a fraction of a second because chromatophore organs are innervated directly from the brain (2, 3). Because of its speed and diversity, body patterning in cuttlefish is the most sophisticated form of adaptive coloration in the animal kingdom (4). Although many aspects of cephalopod vision are known (5), the visual features of a given substrate that evoke adaptive coloration are relatively unstudied.Recently we developed a quantifiable behavioral assay based upon single, static, computer-generated images that allow us to control detailed aspects of visual input. With this method, we first showed that certain visual background features were used by cuttlefish to produce disruptive coloration (6). Specifically, when the size of white squares on a checkerboard was similar to that of the "White square" component in the animal's skin, the cuttlefish produced a disruptive color pattern; this response occurred over a large contrast range and required only that a few white checks be present in the visual background. A subsequent study (7) showed that, to produce disruptive body patterns for camouflage, cuttlefish cue visually on the area-not the shape or aspect ratio-of light objects in a dark substrate. Most recently, we found that if the background was composed of a high density of small light and dark objects, the cuttlefish would produce mottled skin patterns; but if the background was uniform, uniformly stippled skin patterns would be produced (8). We also applied this behavioral assay to the study of the polarization vision of cuttlefish; although the results were mixed, they indicated that cuttlefish perceive differently polarized checks as light or dark objects and