You might think 3-D glasses are a little gimmicky, but they're really trending among invertebrates. A paper published on Thursday in Nature shows that praying mantises see stereopsis (depth perception from two eyes), just like humans do. It's a 3-D world.
Researchers from Newcastle University in England created an "insect cinema" (this is a job people have!) and started showing praying mantises 3-D projections using different human technologies. There was already evidence of stereopsis in insects from a 1983 Nature paper by Samuel Rossel, but the Newcastle researchers wanted to design a more definitive experiment. Insect vision research is about intellectual inquiry, not rivalry, though. "We thank Prof Samuel Rossel for generously making available the custom-built mantis stand used during his own pioneering experiments," the researchers wrote. Insect 3-D high five!
The first experiments used polarized lenses—like the glasses we get at the movies today. For them to work, two projectors run simultaneously, showing views of the same shot with different polarization. The glasses have different a polarization in each lens, so only one image enters each eye. But for this 3-D effect to work, the stimulus has to be directly in the field of vision. The praying mantises were getting too much "crosstalk" in which the two polarized images competed with each other.
Instead the researchers switched to testing out "anaglyph" 3-D, essentially retro red/blue glasses and color encoding. Instead of different polarization for each eye, this technology sorts the images to each eye based on color, producing a composite 3-D image. A press release notes that mantises don't see red light very well, so they got "custom-made glasses with one blue and one green lens!" It's all very exciting. And the approach worked. The researchers write that the blue/green glasses, "clearly succeeded in giving the mantis the illusion of 3D depth." It seems, though, that mantises have monochromatic vision and were actually processing the difference in luminance between the blue and green images.
Back in the "insect cinema," which had a 20.4-inch-wide by 12.8-inch-high screen, the researchers put subjects in the mantis stand and showed them footage of preylike shapes. Without the 3-D effect, the mantises didn't react because they could see that the "prey" was too far away for them to reach. But when the researchers flipped on the 3-D footage, the mantises tried to strike.
“Despite their minute brains, mantises are sophisticated visual hunters," Jenny Read, a professor of vision science at Newcastle who led the study, says in a statement. "Better understanding of their simpler processing systems helps us understand how 3D vision evolved, and could lead to possible new algorithms for 3D depth perception in computers."