Give ‘em the old razzle dazzle, and give it to ’em fast

Why do zebras look like this?

You know. All stripey.

One theory for this “Notice me!” pattern was picked up by naval officials: that the complicated, high contrast shapes somehow made zebras harder to see. Here, we see the HMAS Australia, painted with “dazzle” colouration.

Some said this particular pattern contained a “lady’s leg.” But then, some people see that sort of thing everywhere.

That the advantage of this kind of pattern hasn’t been well tested is maybe not surprising. “Hard to see” is a wide and ill-defined term that could be measured in a lot of ways.

Scott-Samuel and colleagues examined this by showing images with patterns on a computer screen. Their subjects were show two moving blocks, and had to judge which of the two were moving faster. The “dazzle” patterns they used are shown here. They also used a plain white square as a standard to which everything else was compared.

When the patterns moved quickly against a high contrast background, people judged them to be moving slower than the plain white stimulus. Zigzags and checked patterns caused a larger effect (that is, were seen as moving slower) than those with stripes.

How fast do you have to be moving to get this effect? The authors estimate that the tested speeds on the computer screen are equivalent to 13 kilometers an hour for an object about 10 meters away. This is certainly within the range of biological capabilities. I found one site that estimated zebras can run at about 60 kilometers per hour. If a predator thinks an animal is running slower than it is, it could miss what it aims at.

That this effect works with humans doesn’t mean that it will work with other animals, however. For that matter, the effect might be enhanced for other kinds of animals. Different eyes, different possibilities.

It seems to me that this should be possible to test with animals. If you could train a visual predator to get a food reward for striking at a moving target, you would predict that the predator would miss targets with the dazzle patterns more often.

The authors take a more applied view. They do some calculations for a Land Rover under rocket attack. They reckon that the effect of dazzle colouration could be enough for someone to miss the vehicle is they were launching a rocket propelled grenade at it. Sadly, the paper contains no experimental test of this prediction.

Jeeps? Rockets? Now there’s a scientific prediction that has MythBusters written all over it.




Reference

Scott-Samuel N, Baddeley R, Palmer C, Cuthill I. 2011. Dazzle camouflage affects speed perception. PLoS ONE 6(6): e20233. DOI: 10.1371/journal.pone.0020233

Zebra photo by alles-schlumpf on Flickr; ship photo by ; both used under a Creative Commons license.