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Voice of the Lobster (video)
May 09, 2001

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This week’s journal Nature reports that there’s another musician among us who plays a new kind of violin.

But as this ScienCentral News video report shows, this latest virtuoso is more likely to end up on your dinner table than in your CD collection.


How’d they figure this out?

According to Sheila Patek:

"I started by just attaching a sensor on the moving part, the plectrum, and I tracked the movement of that plectrum over the file during sound production. And at the same time I was recording sound underwater. So the first thing I did was to just look at what is the movement that’s involved in producing sound—what’s the plectrum doing? And I established that each time the plectrum moved a little bit of a pulse of sound is produced.

"The next thing I did was to look at the muscle activity of the muscles that are being used to generate this movement. And the question here was—once I established that the structure was moving and each time it made a short, stepped movement it produced a pulse of sound—the question was, are there individual muscle contractions or is it a single muscle contraction that’s pulling the plectrum over the file? Because if it’s a single muscle contraction—just once big pull—yet there’s still stepped movement, that suggests that there are frictional attractions going on between the two surfaces. And that’s what I found.

"The final thing I did was to look at the scale involved and the rate of movement of the plectrum over the file. And I did this by looking at the microscopic anatomy of the shingles on the file—the tiny structures—and at the anatomy of the soft tissue to see how many shingles on this file are being hit per second. I did that by using a high-speed video where you look at a thousand frames per second. So you slow things down a whole lot and then look at how far the plectrum is moving per unit of time. And what I found was that the plectrum is hitting the shingles, the tiny structures on the file, at much much much higher rates than would actually produce each one of those pulsed noises. And that certainly supports the idea that it’s not a hard pick that’s hitting a series of macroscopic bumps, because the rate at which the plectrum is hitting the tiny tiny bumps on the lobster is at about 15,000 hertz as opposed to about 80 hertz. If the lobster’s sound producing mechanism were analogous to a washboard, then the shingle impact rate would have equaled the pulse rate."

High-speed video helps us understand sharks as well

Using similar high-speed video while watching sharks feed, a researcher at the University of Rhode Island was able to deconstruct the unique way a spotted bamboo shark’s jaw works. Biological sciences professor Cheryl Wilga found that the shark lifts its head, depresses its lower jaw, extends its upper jaw, bites, and then retracts the upper jaw under the head. Unlike humans, the shark’s upper jaw isn’t fused to its cranium.

Wilga took measurements of the angle of the shark’s fins, how wide it opens its mouth, and how fast it captures its prey. She also monitored up to twelve muscles with electrodes as thin as pieces of hair, a process called electromyography, to determine which muscles are used.

In her research, Wilga also disproved "the old theory that sharks swim like airplanes fly." That is, it was thought that a shark’s pectoral fins provided lift, but using fluid dynamics and lasers showed that the shark’s body and tail provide the lift, while fins are actually used for steering.




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