Mantises with 3-D glasses let scientists see the world in a new way
If you thought praying mantises already look pretty cool, scientists who put tiny 3-D glasses on the petite hunters have found that their stereoscopic vision system is unlike that of any other known animal.
The findings, described this week in the journal Current Biology, reveal how these remarkable insects have developed a sophisticated ability with such a tiny brain – and could prove useful in designing visual systems for future robots.
Vertebrate animals use their stereoscopic vision to perceive depth. Each eye sees a slightly different image because of its slightly different vantage point, and the brain basically slides those two images together and calculates how far away objects are.
All kinds of animals, including humans, could do this, said senior author Jenny Read, a neuroscientist at Newcastle University in England. But the only known insect to possess this ability is the praying mantis, whose brain has only a million or so neurons compared with the roughly 100 billion neurons in a human brain.
Read and her colleagues have since confirmed research from the 1980s showing that praying mantises really do have 3-D vision.
In a 2016 paper, they used beeswax to stick tiny blue and green 3-D glasses on the faces of praying mantises, and showed them 3-D movies of what appeared to be tasty-looking prey. The insects lunged only at targets in the 3-D movies, not the regular 2-D ones.
3-D vision is a handy ability for praying mantises, which are skilled hunters. But how did such an apparently simple creature develop such a complex ability?
Scientists already know how to confuse human 3-D vision – so they set out to see if praying mantises would also fall for the same tricks.
The researchers showed humans with 3-D glasses images of moving dark and bright dots, except that the image shown to one eye was essentially the photonegative of the other. Because human vision seems to try to correlate the image contrast from each eye’s viewpoint, flipping the contrast in one of them thwarts depth perception. Viewers can’t tell which elements are nearby and which are far away.
The mantises, it turned out, did not suffer from the same problem.
‘‘They were just totally unfazed by this manipulation and kept on striking when objects were near and not when they were far away,’’ Read said. ‘‘That was telling us praying mantises do not use correlation for their stereo vision – at least not the correlation of image contrast. They’re doing something really different.’’
The scientists then took it a step further. They showed each eye a different, uncorrelated set of dots, but both with a moving target passing through them. Again, where the humans failed to perceive when the object was ‘‘close’’, the mantises succeeded.
The scientists think it’s because the insects are not trying to correlate all the details in the images, but instead are looking for changes in the light patterns over time. Basically, they’re looking for only things that move.
There could be a reason for these very different systems, Read said. Human visual systems are very good at picking out the differences in still images, which might help them to better see through camouflage. On the other hand, based on their hunting style, praying mantises might be better served by a system that picks up only the movements of nearby prey.
The findings could help scientists design better computer algorithms for simpler visual processing systems in drones and other robots, the researchers said.
‘‘We think the mantis 3-D algorithm, since it’s simpler, could be implemented into processing systems that require less computing power,’’ said lead author Vivek Nityananda, a behavioural ecologist at Newcastle University. ‘‘It could be implemented, for example, into lightweight robots.’’