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Proceedings of the Royal Society B

Will Wild Mice Use Running Wheels?

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Proceedings of the Royal Society B

Scientists and animal rights activists have long wondered if wheel running was a neurotic behavior exclusive to captive mice. But new research on mice in the wild shows that it's possible these rodents run for fun.

Johanna H. Meijer and Yuri Robbers, researchers at the Leiden University Medical Center in the Netherlands, placed exercise wheels outdoors in two areas—one urban, and one not accessible to the public—in partially enclosed cages to keep larger animals from knocking them over. They pointed video cameras triggered by infrared motion detectors on them. Over the course of the three years, cameras shot 200,000 clips of the wheels in motion.

After analyzing 12,000 clips, the researchers found that feral mice did, in fact, use the wheels: The cameras recorded 734 cases of mice running on the wheel in the urban area, and 232 cases in the private area, over the course of 24 months. Wheel running occurred year-round; the mice were typically juvenile. The mice spent between one and 18 minutes on the wheel. The animals got on the wheel, got off, and within minutes got back on, running away—and they always ran. They never walked.

“When I saw the first mice, I was extremely happy,” Meijer told the New York Times. “I had to laugh about the results, but at the same time, I take it very seriously. It’s funny, and it’s important at the same time.”

Though mice accounted for the vast majority of wheel running observations (88 percent), they weren't the only animal to go for a spin on the wheels: shrews, rats, slugs, frogs, and snails also hopped on (the snails, however, were excluded from the analysis, because they "caused haphazard rather than directional movement of the wheel," according to the study, which appeared in Proceedings of the Royal Society B). Like mice, some shrews, rats, and frogs left the wheel and then entered it again to keep running. "This observation indicates that wheel running may well be intentional rather than unintentional for these animals," the study says.

Though the enclosures at first had food, removing the food didn't stop mice from running. Although the researchers noted that the number of visits to the enclosures dropped after the food was removed, "the fraction of visits including wheel running increased. This implies that wheel running can be experienced as rewarding even without an associated food reward, suggesting the importance of motivational systems unrelated to foraging."

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iStock // Ekaterina Minaeva
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Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
May 21, 2017
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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May 23, 2017
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