Fingerprints with Feeling

December 1, 2009

We all know what fingerprints are for: they exist so dumb crooks can leave them at crime scenes to be discovered by te folks from CSI.  Certainly, their role in forensic science is important, and has been at least since Francis Galton published his report on the classification of fingerprints [PDF]  in the Philosophical Transactions of the Royal Society in 1891.

It has been known for some time that those ridges and valleys on our fingertips help to improve our grip, by increasing the friction between our fingers and a grasped object.  Now the Physics arXiv blog at Technology Review has an article describing some new evidence that fingerprints serve a useful sensory function.  Our perception of texture depends on sensing minute vibrations as we brush our fingers against a surface.  The neural receptors that do this are called Pacinian corpuscles.  They are quite sensitive, but only in a narrow range of frequencies, centered at about 250 Hz.

Investigators at the University of Paris, led by Georges Debregeas, found that fingerprints play an important role in this process.  In essence, they built an electro-mechanical replica of a finger, complete with fingerprints, and instrumented with high-resolution sensors.  They found that fingerprints act to amplify vibrations in a particular frequency range:

They say that fingerprints resonate at certain frequencies and so tend to filter mechanical vibrations. It turns out that their resonant frequency is around 250 Hz. What an astonishing coincidence!

This “signal processing” allows us to feel surface changes on a scale considerably smaller than the distance between Pacinian corpuscles. (The paper is available here; there is a copy of the abstract and a link to the full article PDF.)

One of the questions that has puzzled neurobiologists and people working in robotics is how people manage to get it all together.  The amount of processing power that would seem to be required to keep a person walking, talking, and breathing considerably exceeds the best estimates of what the brain alone can actually do.  These results are another bit of evidence for the proposition that the brain actually depends on other parts of the body to do significant pre- and post- processing of information, in order to keep things going.

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