Zebra stripes generate a form of motion camouflage – researchers

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A zebra in South Africa.
Striking zebra stripes are used in a form of motion camouflage, researchers believe.

The motion of  the high-contrast stripes of zebras creates visual effects that may act as a form of motion camouflage, researchers believe.

The scientists, in a paper published in the journal, Zoology, believe an observer’s visual system is flooded with erroneous motion signals, to confuse the likes of insects approaching from the air or even mammalian predators.

The study was carried out by Martin How, of the Brain Institute at the University of Queensland, and Johannes Zankerb, from the Department of Psychology at the Royal Holloway University of London, in Surrey.

How and Zankerb said the functional significance of the zebra coat stripe pattern was one of the oldest questions in evolutionary biology, having troubled scientists ever since Charles Darwin and Alfred Russel Wallace first disagreed on the subject.

“While different theories have been put forward to address this question, the idea that the stripes act to confuse or ‘dazzle’ observers remains one of the most plausible,” they said.

“However, the specific mechanisms by which this may operate has not been investigated in detail.”

The pair set about investigating how motion of the zebra’s high-contrast stripes creates visual effects that may act as a form of motion camouflage.

They simulated a biologically motivated motion detection algorithm to analyse motion signals generated by different areas on a zebra’s body.

“Our simulations demonstrate that the motion signals that these coat patterns generate could be a highly misleading source of information.”

They suggested that the observer’s visual system is flooded with erroneous motion signals that correspond to two well-known visual illusions – the wagon-wheel effect (perceived motion inversion) and the barber-pole illusion (misperceived direction of motion).

They predicted that these two illusory effects act together to confuse biting insects approaching from the air, or possibly mammalian predators during the hunt, particularly when two or more zebras are observed moving together as a herd.

Martin J. How, Johannes M. Zanker, Motion camouflage induced by zebra stripes, Zoology, Available online 4 December 2013, ISSN 0944-2006, http://dx.doi.org/10.1016/j.zool.2013.10.004.

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