"morphological computing"

Fingerprints: Signal Processors for Touch
Debregeas et amis say it looks as if the ridges and whorls in fingerprints filter mechanical vibrations in a way that best allows nerve endings to sense them. The mechanoreceptors that do this job are called Pacinian corpuscles. They sit at the ends of nerves and are responsible for sensing pressure and pain. These devices can sense vibrations over a wide area of skin but are sensitive only to a limited range of vibrations. In fact biologists have known for some time that Pacinian corpuscles are most sensitive to vibrations at 250Hz.

Debregeas and co have investigated this problem using a "CYBER FINGER" that they built in their lab, complete with synthetic fingerprints on the same scale as human ones and a microelectromechanical sensor that measures force with a spatial resolution of millimetres. They say that fingerprints resonate at certain frequencies and so tend to filter mechanical vibrations. It turns out that their resonant frequency is around 250Hz.

That means that fingerprints act like signal processors, conditioning the mechanical vibrations so that the Pacinian corpuscles can best interpret them. It's this optimisation process that allows us to sense textures with a spatial resolution far smaller than the distance between Pacinian corpuscles in the skin.

There is a growing awareness that the processing power of the nervous system, including the brain, simply cannot handle the volume of number crunching that has to be done to keep a living body on the road. Instead, it looks increasingly clear that the brain outsources much of this work to the body itself: to the joints, ligaments, muscles, skin etc. Understanding how these materials do all this processing is turning materials science into a branch of computer science. It's even got a name: morphological computing.

People Hear With Skin as Well as Their Ears

The researchers had subjects listen to spoken syllables while hooked up to a device that would simultaneously blow a tiny puff of air onto the skin of their hand or neck. The syllables included "pa" and "ta," which produce a brief puff from the mouth when spoken, and "da" and "ba," which do not produce puffs. They found that when listeners heard "da" or "ba" while a puff of air was blown onto their skin, they perceived the sound as "ta" or "pa."

Dr. Gick said the findings were similar to those from the 1976 study, in which visual cues trumped auditory ones -- subjects listened to one syllable but perceived another because they were watching video of mouth movements corresponding to the second syllable. In his study, he said, cues from sensory receptors on the skin trumped the ears as well. "Our skin is doing the hearing for us," he said.

"What's so persuasive about this particular effect," he added, "is that people are picking up on this information that they don't know they are using." That supports the idea that integrating different sensory cues is innate.

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5 Responses:

  1. dasht says:

    Doesn't that seem like one of those "slap your forehead, we should have looked for this years ago" kind of things? Like, if someone told you the mere hypothesis and forced you to bet yes or no pending empirical investigation, you'd go "Damn, that's clever and obvious in retrospect - I bet 'yes'".

    A related thing I've heard of (all rumor and inuendo, no links) is supposedly there is some research that shows that cats' whiskers are tied to their visual fields. E.g., a cat stalks, closes in on prey, and - as cat owners can see - when cats are agressive close up their whiskers push forward - just right to envelope prey - and supposedly the mechanical signals from those whiskers help them "visualize" what's going on near their mouths.

    • dasht says:

      we're all synthetics - differing only in degree.

    • dasht says:

      also, (aside from sorry to be such a bore with so little snark and so much random bs-i'm-thinking-of to offer here) --- isn't the conventionally told / depicted Helen Keller breakthrough scene (her return to language) centered around involving Keller's hands in perceiving speech? The whole "wawa" (water) thing? Suggesting a kind of "Aha! Same signal, different channel!" kind of catharsis.

    • lionsphil says:

      Basically.

      High speed photography reveals that when a cat is unable to see its prey because it is too close to its mouth, its whiskers move so as to form a basket shape around its muzzle in order to precisely detect the prey's location.

  2. xthread says:

    That means that fingerprints act like signal processors, conditioning the mechanical vibrations so that the Pacinian corpuscles can best interpret them. It's this optimisation process that allows us to sense textures with a spatial resolution far smaller than the distance between Pacinian corpuscles in the skin.

    That's right up there with the way that your visual system is synthesizing focus and object / edge detection. I don't know that we synthesize a higher visual resolution that our rods and cones can directly support, but I'd be pretty surprised if we don't.