Motion illusions for defence

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High-contrast colour patterns, such as black and white stripes, can move in a way that interferes with how animals, including humans, detect and perceive motion. For instance, objects become blurred when moving quickly enough, and when the diagonally-striped poles outside barber shops rotate horizontally they create an illusion of the stripes moving vertically. In our project, we aim to understand whether and how these 'dazzle' illusions are used by prey to escape their predators. While the colour patterning of animals is one of their most obvious features, dazzle colouration must be paired with particular ways of moving to be effective; for the first time we will quantify both colour and movement in our study. Obtaining an understanding of how dazzle colouration operates in the real world will help explain the enormous diversity of conspicuous colour patterns displayed by animals. There is also practical application in understanding how motion illusions can be exploited, or indeed minimised depending on the need, in safety and defence industries.Whilst the idea of dazzle colouration was proposed over a century ago and was potentially exploited by Allied ships in WWI and WWII to avoid torpedo-wielding enemy U-boats, it has only received serious scientific interest over the past decade. Even then, studies have almost exclusively relied on proxies for real predators by using humans 'attacking' computer-animated prey that have colour and movement patterns not necessarily found in nature. A better understanding of how dazzle illusions may actually operate in nature, and thus how they may be exploited in real-world scenarios, ultimately requires studying natural systems in the same contexts and environmental conditions within which they have evolved.In our project we will exploit the extraordinary diversity of colour patterns seen in fish to determine whether different types of colour pattern are linked to how fish move. We will then test whether these motion-colour combinations maximise the production of dazzle illusions and how this benefits prey fish attacked by real predators, and whether the dynamic nature of dazzle colouration makes it harder for predators to learn to counteract illusions and defeat their illusionist prey. We predict that dazzle-coloured prey benefit by being camouflaged (i.e. reducing detection from predators), reducing the frequency of attacks by confusing predators, and reducing successful capture after they are attacked by misdirecting the attacks of predators. We will use mathematical models of the motion-processing cells within animal visual systems to objectively quantify, from a predator's perspective, illusions across multiple prey fish species. Initial data from four species of closely-related zebrafish that display very different colour patterns suggest that by just changing the orientation of stripes, fish can either become camouflaged or create an illusion of movement in a different direction to true motion, which could affect the ability of predators to accurately target their prey. We will test whether these illusions are beneficial for prey by allowing natural predators to hunt and attack realistic robotic prey that closely match the illusionist's colouration, shape and movement. This will be the definitive study that tests whether motion illusions occur in nature, and whether they can create enough interference in the visual system of predators to benefit real animals. The results from our project may have applications for low-tech military confrontations that use visual systems to intercept moving targets, and also for road-user safety where the blending of stripes at high speeds can be exploited by stripe patterns across the road or on emergency vehicles under scenarios that require a careful perception of speed by pedestrians, cyclists and motorists.