Investigating depth perception in non-human vision using the dynamic camouflage of cuttlefish

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The complexity of animal colouration patterns suggests we are not alone in our rich perceptual experience of the visual world. For instance, perceptual tricks and optical effects (visual illusions) are common in animal body patterns that convey camouflage. As these have evolved to defeat visual detection or recognition by non-human viewers, their effectiveness against our own visual system suggests common principles of visual processing. The perception of depth is important for interacting with a visually complex environment, a task that is by no means unique to humans. We perceive depth even in the absence of binocular cues, as is simply illustrated by considering a photograph: it is usually trivial for us to interpret depth from this two-dimensional rendition of a three-dimensional scene using cues such as perspective, shading and shadows. Although the ability to perceive visual depth has been clearly documented in many groups (e.g. reptiles, insects and birds) it is more difficult to determine what perceptual processes might be used by non-human animals. There is currently no systematic research on pictorial depth perception in a non-primate system.This project will study the camouflage behaviour of the cuttlefish Sepia. Sepia offers a unique system for investigating non-human visual perception because each animal can produce thousands of different body patterns for camouflage. The particular pattern that an animals expresses reveals a great deal about its visual perception: how it sees patterns, shapes and objects around it is reflected in the body pattern. These body patterns are determined by direct visual assessment of the local environment and the chromatophores that form them are under neural control. Therefore we are afforded a direct link between visual input and body pattern output via the brain, allowing novel insight into its visual mechanisms. This system is all the more fascinating because cuttlefish are molluscs whose eye and brain have evolved independently from vertebrates, as the common ancestor of vertebrates and molluscs had rudimentary vision at best. We know that the camera-type eyes of cephalopods are highly convergent with the vertebrate eye, and research to date suggests that similar principles underlie the ways in which these two groups process visual information. This proposal aims to understand how depth cues, be they actual or pictorial, influence the camouflage response of Sepia, and how in turn this affects its detectability by potential predators.In this project I will explore the importance of depth and perspective in the cuttlefish visual system, and what part it plays in making and breaking camouflage. I will achieve this through laboratory and field behavioural experiments and image analysis. The ability to test the response of Sepia to isolated visual information means we can take an approach similar to that used in human psychophysics, testing a series of carefully controlled parameters in turn to build a complete picture of how depth is perceived and used by this animal. However, the biological relevance of such isolated cues in artificial stimuli to the animal is limited, and its visual ecology should not be neglected. Therefore this proposal complements a laboratory based "psychophysics" approach with fieldwork. The body patterns of Sepia are believed to have evolved largely in response to predation pressure from teleost fishes; a further component of this proposal will determine how changes in Sepia's body patterning affect detection and recognition by teleost fishes, a subject largely neglected in studies of Sepia vision and camouflage to date. This work will provide new insights into both non-human visual processing and camouflage making and breaking.