Animal programs

Vision control movements seen in fruit flies may have evolved to conserve energy and improve performance

Fruit flies synchronize their head and body movements to stabilize their vision and fly efficiently, according to Penn State researchers who used virtual reality flight simulators. The finding appears to hold true in primates and other animals, the researchers say, indicating that animals have evolved to move their eyes and bodies independently to conserve energy and improve performance. This understanding could inform the design of advanced mobile robots, according to lead researcher Jean-Michel Mongeau, assistant professor of mechanical engineering.

The researchers published their results yesterday, May 3, in Proceedings of the National Academy of Sciences.

“We found that during gaze control, fruit flies minimize energy expenditure and increase flight performance,” Mongeau said. “And, using this coordination information, we have developed a mathematical model that accurately predicts similar synchronization in [other] visually active animals.

The researchers used high-speed cameras to record a fruit fly surrounded by LED video screens onto which the researchers projected images of what a fly would see in flight, creating an immersive virtual reality experience and moving the fly as if flying freely.

“When a fly moves, it coordinates its head, wings, and body to fly through the air, escape predators, or search for food,” Mongeau said. “We were interested in studying how flies coordinate these movements, and we did this by simulating flight in virtual reality.”

Responding to both slow and fast visual movements in the virtual reality flight simulator, the fly moved its head and body at different rates. The researchers took measurements and tracked the movements of the fly’s head to determine the direction of its gaze, as its eyes are fixed on its head and cannot move independently.

“We found that the movements of the fly’s head and body were complementary, in that the body moved the most during slower visual movements, while the head moved the most during faster movements.” said Mongeau. “The body and head working together helped stabilize the flight motion from very slow to very fast.”

Testing the concepts further, the researchers immobilized the fly’s head and subjected it to the same visual stimuli. They found that the fly could not respond to rapid visual movements, demonstrating the benefit of complementary body and head movements.

“We’ve found that the head and body working together is advantageous from an energetic perspective,” Mongeau said. “Because the head is smaller, it has less resistance to movement, or inertia, which means it can react to fast movements, while the much larger body responds better to slower movements. tuning these two components saves energy and increases performance not only for flying it, but also for other animals.”

Using control theory, a branch of engineering that deals with the design of feedback systems like autopilots, the researchers compared the results of the fly’s movements to other animals, including a classic study of primate movements.

“Using the same model, we looked at eye, head, and body inertia ratios elsewhere in the animal kingdom, including other insects, rats, and birds,” Mongeau said. “The way flies move their heads and bodies is very similar to the way primates move their heads and eyes, which is remarkable since they diverged hundreds of millions of years ago.”

Just as a head is lighter than a body, eyes are lighter than a head and require less energy to move. According to Mongeau, independently moving eyes and heads marked the transition from water to land in the vertebrate fossil record.

“As vertebrate animals moved from water to land more than 350 million years ago, developing mechanisms to control head and eye movements could have had substantial evolutionary benefits,” said said Mongeau. “We found that there is a sweet spot in eye-head-body ratios, suggesting that inertia may have been an important constraint in the evolution of vision.”

The researchers’ findings could be used to improve the energy efficiency and performance of robotics, according to Benjamin Cellini, a doctoral candidate in mechanical engineering and first author of the paper.

“In robotics, sensors are usually fixed,” Cellini said. “But in the animal kingdom, sensing and movement are coupled, because many physical sensors, like eyes, move. Inspired by biology, we can design more energy-efficient robots by making vision-based sensors mobile. .”

Wael Salem, a doctoral student in mechanical engineering, is co-author of the article.

The United States Air Force Office of Scientific Research and the Alfred P. Sloan Fellowship supported this work.