Motion camouflage is a stealth technique that allows a predator to sneak up on their prey. Insects, such as male dragonflies, achieve this by closing in on their prey along a path so that - to the prey's eye - they seem to remain distant and stationary at a fixed point. They do this by keeping themselves positioned between a fixed point in the landscape and their moving prey. For example, if the predator were to start its approach positioned in front of a rock, it would ensure that it is always positioned directly between the rock and the prey. As the watching prey moves, the image of the predator - like the image of the rock - would thus appear not to move laterally, making a stealthy approach less likely to be noticed.

To test whether humans were psychologically vulnerable to this illusion, researchers, Andrew Anderson and Dr Peter McOwan, at the Department of Computer Science at Queen Mary conducted experiments under the guise of a week-long games competition - with prizes - for staff and students.

In their purpose-written three-dimensional computer game, called 'Missile Defence', the player (the prey) moved in a straight line down the centre of a virtual tunnel, floating in which were stationary missile-launchers (the fixed point). The launchers would fire at the player either a normal missile or a missile (predator) that followed the motion camouflage strategy. Players then had to try and shoot down the missiles aimed at them before they themselves were hit.

They found that the camouflaged missiles were able to get much closer to the target than the others before being shot.

The remarkable thing, says Anderson, is that these complex trajectories can be worked out by an artificial intelligence (AI) computer program based only on the movement of the target as seen from the viewpoint of the missile. There is no need for sensors to keep track of the fixed spot. You can train a system to estimate its relative position without giving it 360-degree vision.

The AI program could be used to allow software agents in computer games to sneak up on players or, in a more serious scenario, in future generations of anti-aircraft missiles, which could be made far harder to dodge by a guidance system inspired by this research.

For full coverage, please read "Dragonfly trick makes missiles harder to dodge" from the New Scientist or "Humans deceived by motion illusion" from the Australian Broadcasting Company. For technical details, please see Andrew's page.