The psychologist Niko Troje's young daughter observed that she can approach wild rabbits more easily on bicycle than on foot. But when she asked her father why is that he could answer. "I didn't have an answer for her then," said Troje, of Queen's University. "Now, I think I have one."

He, Dr. Cord Westhoff from the Ruhr-Universität Bochum in Germany and their colleagues studied how humans detect and interpret movement. The Motion Capture Laboratory at Queen's uses high speed cameras to track the three-dimensional trajectories of small reflective markers attached to the central joints of a person's body. Although the set of all these white marker dots alone might seem to provide only very scarce information, researchers found that when the subject moves, these white marker dots move in an organized fashion from which observers can determine the gender, body build, emotional state, and other attributes. In other words, we are able to deduce quite a lot of information about somebody without paying too much attention to details.

In this study, Dr. Troje's team captured the motion of cats, pigeons and humans and then showed the video of the moving markers to various volunteers. The markers were changed in various ways and researchers wanted to see whether the participants could still tell the direction of movement.

Somewhat surprisingly, scrambling the dots didn't create a problem. However, when the image was inverted upside down, observers were no longer able to say if the animal was moving to the right or left. Researchers have concluded that to humans, and likely to other animals, the observation of foot movement is an independent, important visual cue for judging whether another animal is approaching. "We believe this visual filter is used to signal the presence of animals that are propelled by the motion of their feet and the force of gravity," said Troje. "The observation that it is relatively easy to get close to wild animals in a car, a canoe, or a similar vehicle might be due to the absence of the typical movement of the feet."

Scientists think this locomotion detector is part of an evolutionarily old system that helps animals quickly detect whether a potential predator or prey is nearby, even if it's just in their peripheral vision. While this interpretative part of the brain is fueled mainly by visual information in case of humans, in case of other animals such as rabbits auditory signals may also play an important part. Other research has also suggested that even newly hatched chicks also use this system. "It seems like their brains are 'hard wired' for this type of recognition," Troje said.

This discovery can also explain the hunting tactics of various animals such as cats. "The creeping movement of a hunting cat can be interpreted in terms of disguising the ballistic component in its locomotion," he adds. Furthermore, we may also understand "seemingly irrational phobias" towards animals that use uncommon locomotion systems - "snakes, insects and spiders, or birds can generate pathological reactions not observed in response to 'normal' animals."