By fitting tiny glasses to praying mantises, researchers from Newcastle University in the UK have confirmed that the insects have 3D vision.
The findings of the study, published in the journal Scientific Reports on Jan. 7, is significant because 3D vision, also known as stereopsis, had only been confirmed in vertebrates such as humans, birds, mammals and reptiles.
Creatures that see in stereopsis use differences in the location of an object as perceived by their right and left eye to determine the proximity of this object. The ability to judge distance is crucial for predators that hunt for food and preys that try to evade becoming dinner.
In the 1980s, University of Zurich scientist Samuel Rossel conducted a study about the binocular vision of praying mantises, but the results were limited. The early study had less sophisticated means of testing 3D vision in praying mantis since the occluders and prisms used only provided a small set of images.
For the new study, Jenny Read and colleagues fitted praying mantises with miniature 3D glasses similar to the old school glasses used when watching 3D movies. For human wearers, the glasses have a blue lens and a red lens, but since mantises see green light much better than red, the researchers developed glasses with a green lens and a blue lens.
Read and colleagues initially used contemporary 3D technology that uses circular polarization for separating the two eyes' images, but it did not work. The mantises were very close to the screen that the glasses fitted to them were not able to correctly separate the images.
"Since red light is poorly visible to mantises, we used green and blue glasses and a LED monitor with unusually narrow output in the green and blue wavelength," said study researcher and sensory biologist Vivek Nityananda.
The researchers then showed the mantises short videos of similar bugs that move around a computer screen, sort of like a cinema for insects. They observed that the mantises did not attempt to catch the bugs when they were in 2D but struck out at the images when they were shown in 3D. These behaviors confirmed that mantises are capable of using 3D vision.
Read said that mantises are sophisticated visual hunters marked by terrifying efficiency when capturing prey. By studying how these creatures perceive the world and having a better understanding of their processing systems, researchers can better understand the evolution of 3D vision.
"We thus definitively demonstrate stereopsis in mantises and also demonstrate that the anaglyph technique can be effectively used to deliver virtual 3D stimuli to insects," the researchers wrote in their study. "This method opens up broad avenues of research into the parallel evolution of stereoscopic computations and possible new algorithms for depth perception."
