Miniature 3-D glasses for praying mantises seem like a great idea, even if only for the entertainment value. We get to enjoy photos like the one above, while the mantises look cool and get a more immersive movie-going experience.
But these glasses aren't just for human amusement or mantis matinees. Designed by scientists at Newcastle University in England, they're part of a new study that could deepen our understanding of depth perception. Not only does it confirm mantises hunt with 3-D vision, which has yet to be proven in other invertebrates, but it may also help us develop better algorithms for visual perception in robots.
Almost everything scientists know about 3-D, or stereoscopic, vision comes from studying mammals and other vertebrates, the study's authors note in the journal Scientific Reports. This ability wasn't documented in an insect until the 1980s, when German zoologist Samuel Rossel reported "the first unequivocal evidence for stereoscopic vision in an invertebrate," specifically a praying mantis.
But that research was limited by a reliance on prisms and occluders, the new study's authors say, meaning mantises could only be shown a small set of images. Without a better way to test insects' depth perception, the research stalled for 30 years. Only now, with these shades, are the secrets of mantis vision coming into view:
"Despite their minute brains, mantises are sophisticated visual hunters which can capture prey with terrifying efficiency," study leader Jenny Read says in a press release. "We can learn a lot by studying how they perceive the world."
Read and her colleagues started by designing and building an "insect cinema," where they tested various strategies. They settled on old-school 3-D glasses, although the eyewear needed a couple adaptations for mantis anatomy.
For one thing, praying mantis heads can't hold glasses the way human heads do. While our eyewear rests on two outer ears, most praying mantis species have only one ear — and it's located in the center of the thorax, not on the head. To solve that problem, the researchers used beeswax to stick lenses onto the mantises' eyes.
(As unpleasant as that sounds, the researchers have previously explained that beeswax makes the glasses easy and harmless to remove.)
Lens color was another hurdle. While traditional 3-D glasses have a blue lens and a red lens, red light is poorly visible to mantis eyes. To give their insects a similar experience, the researchers simply replaced the red lens with green.
Once their shades were on, the mantises watched short videos of simulated insects moving on a screen. They didn't bother trying to catch any when the fake prey was shown in 2-D. When the movie switched to 3-D, however — making "insects" seem to float in front of the screen — the mantises struck out as they would at prey.
"We definitively demonstrated 3-D vision or stereopsis in mantises," says co-author and Newcastle biologist Vivek Nityananda, "and also showed that this technique can be effectively used to deliver virtual 3-D stimuli to insects."
On top of that, demystifying the mechanics of 3-D vision could lead to better robots and computers, the researchers add. Biomimicry — the art of taking practical inspiration from evolution — is already a major source of innovation in all kinds of technologies, and now it may help mantises teach us to improve artificial eyesight.
"Better understanding of their simpler processing systems helps us understand how 3-D vision evolved," Read says, "and could lead to possible new algorithms for 3-D depth perception in computers."
That will likely take some time, since Read and her co-authors still don't fully understand how mantis depth perception works. But in the meantime, at least the mantises should have plenty of 3-D blockbusters to keep them entertained.