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Flies run on tiny treadmills, watch videos for science

Stanford scientists set flies up on a fly-sized treadmill, showed them videos, and discovered a common thread between the insects and humans.

Fly on a treadmill ball
This isn't about exercising your flies. Video screenshot by Amanda Kooser/CNET

Jeff Goldblum may have had more in common with that housefly he accidentally melded with in "The Fly" than his character ever suspected. A team of Stanford University researchers have determined that both flies and humans have a similar way of perceiving motion.

The researchers figured this out by placing flies on a tiny movable ball that acted like a mini, multi-directional treadmill. The flies were shown movies and had their movements monitored, since fly behavior is to turn in the direction of motion.

On the human side of the equation, the researchers monitored scalp electroencephalogram signals while the subjects watched videos. The participants then completed a questionnaire about their perception of motion in the videos. The researchers say both humans and flies pick up a moving object's speed, direction, and brightness.

The videos used in the study wouldn't make for the most scintillating entertainment. They consisted of black and white geometric shapes moving in patterns. The humans, for example, viewed video of rapidly shifting small squares that together give a sense of motion and reported back about which way they thought the movement was going.

"What's really exciting to me is that no one would have expected this deep similarity between two animals that are so evolutionarily different," Stanford neurobiology professor Thomas Clandinin said.

The study was published in this month's issue of the journal Nature Neuroscience with the title "Flies and humans share a motion estimation strategy that exploits natural scene statistics."

Though the last common ancestor between flies and humans was more than 500 million years ago, our shared environment seems to have driven us in the same direction when it comes to motion perception. "The ultimate hope is by finding an example of how flies solve this particular problem," said neuroscientist James Fitzgerald, "it could give us some insight into how the brain solves problems more generally."