Praying Mantis: 3-D Vision Confirmed With Miniature 3-D Glasses

A pair of miniature glasses developed by scientists at Newcastle University has confirmed that praying mantises use 3-D vision, a piece of knowledge that can help improve the current model of robotic visual perception.

The team confirmed mantises' use of stereopsis, or 3-D perception, in hunting through a specifically-designed "insect cinema" that utilized colored 3-D glasses similar to the older blue-and-red models previously used in movie theaters. The mantises have poor perception of red light however, so green was substituted and paired with blue on the insect glasses, according to a news release.

The study, led by Jenny Read, a professor of vision science, outfitted the mantises with tiny glasses attached with beeswax. The team then proceeded to show the insects short videos of simulated bugs, projected onto a computer screen. Interestingly, the mantises did not attempt to hunt the simulated bugs when they were shown in 2-D, but once shown in three dimensions - as if floating in front of the screen - the mantises struck. 

Samuel Rossel, a scientist with the Department of Zoology at the University of Zürich, originally showed stereopsis in mantises in a 1983 study, but his work featured only prisms and occluders (vision blockers), which limited the amount of images that could be shown. Read's study, however, allowed for any number images to be projected due to the miniature glasses.

"Despite their minute brains, mantises are sophisticated visual hunters which can capture prey with terrifying efficiency. We can learn a lot by studying how they perceive the world," Read said. "Better understanding of their simpler processing systems helps us understand how 3-D vision evolved, and could lead to possible new algorithms for 3-D depth perception in computers."

In the beginning of the study, the team attempted to use circular polarization - the most widely used 3-D technology nowadays - to separate the images for both of the insect's eyes, but it failed due to the short distance between the mantises' eyes.

"When this system failed we looked at the old-style 3-D glasses with red and blue lenses," Vivek Nityananda, a sensory biologist and team member, said. "Since red light is poorly visible to mantises, we used green and blue glasses and an LED monitor with unusually narrow output in the green and blue wavelength."

"We definitively demonstrated 3-D vision or stereopsis in mantises and also showed that this technique can be effectively used to deliver virtual 3-D stimuli to insects," he added.

The team plans to use this development to further explore how depth perception in insects can show the evolution of human vision, as well as add to 3-D technology in computers and robots.

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