Motion illusions for defence

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.

Dazzle illusions are created when constraints in the motion processing cells of visual systems are exploited by moving high-contrast colour patterns, creating a perception that differs from reality. Although high-contrast paint designs were used on allied ships during WWI and WWII to deceive enemy U-boats, how dazzle illusions can reduce the risk of attacks in the natural world and their potential applications in industry have hardly been explored. Previous studies of how colour and movement patterns create dazzle illusions, studied almost exclusively in humans attacking computer animations, have produced equivocal results, perhaps because illusions are sensitive to non-standardised environmental factors. Understanding how illusions may operate in nature requires studying the animals that evolved them for defence. We will conduct the first systematic study investigating how dazzle illusions benefit real animals under realistic scenarios. Predation is one of the strongest forces leading to deceptive adaptations, and we will exploit the extraordinary diversity in colour and movement of freshwater fish within a predator-prey context to address whether and how dazzle illusions are used in nature. We will use recently designed Elementary Motion Detector models to identify and categorise dazzle in 24 species of fish that display variation in high-contrast colour patterns, predicting that colouration and movement parameters are correlated, and observed combinations create stronger illusions than expected from random combinations. We will then create biomimetic robotic versions of these fish to test how illusions affect hunting behaviour in natural predators across three stages of predation: reducing detection via camouflage, reducing attack via confusion, and reducing capture via misdirection. Finally, we will use predator learning assays to test whether the dynamism of motion illusions reduces the ability of predators to learn and circumvent them.

Our proposal primarily addresses questions relating to animal perception and cognition. We envisage several applications for this work whose utility will become clear at during the project's progress.

Road safety
Research on road use has shown that driver behaviour can be influenced by the colour patterns that mark roads. We believe that dazzle illusions have potential for facilitating this behaviour since their dependence on the speed at which objects pass across the visual field may be exploited in a safe manner that causes drivers to exercise greater caution in high-risk areas. Conversely, the high visibility blue-and-yellow checkered patterns favoured by emergency vehicles may actually be detrimental when it comes to accurate speed judgement by pedestrians and drivers of other vehicles, which could lead to fatalities. Alternative designs that combine high visibility with unbiased speed judgement may be suggested by our research, results which would be communicated, as a priority, to the DfT's Science Advisory Council.

The military
Vehicles moving at speed might benefit from dazzle illusions in low-tech war zones that use visually guided projectiles. For instance, a recent paper by NSS and IC calculated that the dazzle illusions created by longitudinal stripes in a moving Landrover may feasibly cause a RPG launcher to miss the target by enough distance to increase the survival of the occupants.

Benefits to animal welfare, in concordance with BBSRC's strategic priorities
Experimentally studying predator-prey interactions in vertebrates is difficult due to the potential for suffering experienced by prey being predated within the unnatural confines of laboratory settings. The modelling, simulation and robotic methods we will use in this project mean that we will be able to study almost all stages of the predation sequence without allowing a single animal to be killed by a predator, or even live prey being exposed to live predators. Beyond the significant step forward for animal welfare in general, this will also greatly benefit academics studying predation in a more controlled manner, particularly in the UK and EU where ethical regulations are stringent.

Software development
We will develop and publicly release a software toolkit to enable other workers to use our method workflow via an ImageJ-compatible GUI software package. This would be an add-on to the already successful Multispectral Image Calibration and Analysis Toolbox, developed by JT (http://www.jolyon.co.uk/myresearch/image-analysis/image-analysis-tools/). Using this software, a researcher will be able to photograph an animal or object using a regular digital camera, use sophisticated modelling techniques to assess its visibility whilst under motion to different visual systems, simulate consequences of manipulating colour patterns, and create life-like biomimetic models of the animal or object to use in carefully-controlled experiments. We foresee this method may be used in a similar way for testing in silica dazzle-coloured vehicles (including drones and military vehicles).

The public
Animal coloration, particularly from the perspective of illusions, provides an excellent platform for explaining scientific concepts from evolution to perception to the general public and to school children.