Sensors / Pierce Crosby & Rachael Johnson on Motion Sensing The Ballet
“Our project is a scientific look at what the arts might mean,” said Pierce Crosby. He stood beside Rachael Johnson onstage, presenting a project where they’d recently strapped motion sensors on the ankles of two dancers—one expert, the other amateur—while they executed ballet moves. Crosby and Johnson were journalism students in Mark Hansen’s class on Formats, Protocols and Algorithms in the past school year. Their goal was to encode “grace” in data, finding the figures behind the performance.
“Grace is basically a fluidity of movement that’s created by muscle contractions made to look effortless,” Johnson said. But that definition was too broad, so the pair decided to focus on sensing motion in three specific movements in ballet: the tendu, the sauté, and the tamble.
The researchers chose to use accelerometers instead of a motion capture system because they could get those over-the-counter, and they bought a Nintendo Wii Remote for $30. They connected the system to the computer via Bluetooth, and loaded up a program called OSCulator—which reads in data every hundredths of a millisecond, depending on where the Wii Remote is pointed toward. Then they programmed a simple Python program to crunch the numbers.
Visually, each move, encoded in data, looked like a kind of polygraph—for the tendu, there were three valleys, four peaks. The journalists had the dancers do each move five times in a row, and looked at the plots.
The professional dancer had jump patterns that were similar each time; the amateur ballerina had more erratic graphs. The journalists’ outcomes and findings, thus, was that precision and consistency in repetition is somehow indicative of grace in ballet.
“For future ideas, we think there’s a lot of great implications for ballerinas overall,” Crosby said. (It had just been revealed that he was the mystery amateur ballerina.) “What this could mean for medical compensation is an example—they exert a lot of force on their bodies.”