Not long ago, we published an article about a breakthrough in allowing the visually-impaired to “see” what is in front of them in the form of computer-mediated audioscapes generated from camera images. It turns out that the sensory substitutions don’t end there, though. A separate project at Colorado State University is developing techniques to allow people to “hear” with their tongue.

Researchers John Williams (L), Leslie Stone-Roy (C), and JJ Moritz (R) - (Photo credit Colorado State University)

The principle behind the system is somewhat akin to Braille, the tactile writing system that consists of patterns of raised dots on paper (and, more recently, refreshable pin displays). Just as the fingers (the sense of touch) can be trained to recognize the dot patterns as letters, so can the tongue.

The tongue, just like the fingers, has a high density of nerve endings and a refined ability to detect minute differences in tactile sensations, even those that are relatively close together. The method used for training the brain to reinterpret those signals (which testers have described as feeling like champagne bubbles or Pop Rocks) is also similar—repeated exposure to a pattern while presenting an example for association. In that respect, the scientists say that the device may be best suited for patients who still have some vestige of hearing—the brain can be trained by playing them the audio of the word at the same time that they are hearing it, so the association will form naturally.

The device is considerably more cumbersome than the EyeMusic setup that allows “seeing” through the ears (which is a relatively unobtrusive set of headphones and sunglasses with a camera mounted on them, linked with a smartphone). A tab, like an over-sized tongue depressor made out of a circuit board, is inserted into the mouth, rendering speech more-or-less impossible while in use.

(Photo credit Colorado State University)

Yet scientists believe that this may be a less invasive method than the cochlear implant surgery it is designed to supplant. Eventually, they hope to reduce the size and shape of the device to that of a common dental retainer, and get rid of the wires that are currently attached to power the device. The whole thing operates at 5 volts and uses Bluetooth for the connection to the external microphone.

Cochlear implants still make use of the brain’s hardwired audio system, however; they also use a microphone to catch sounds, but instead of routing the audio information to another sensory system, they simply bypass the damaged parts of the ear and transmit impulses directly to the still-functional auditory nerve.

Because of that process, they are not effective for deaf patients who have had damage to the auditory nerve or who have only moderate hearing loss. It’s also an irreversible process: the implantation procedure typically results in the loss of some or all remaining natural hearing ability the patient may have retained. The surgery required to implant them also carries risks inherent to any invasive procedure, and can be expensive to undergo— Kortny Rolston, at boingboing, estimates the total costs of the process, from screening to follow-up, at $100,000.

The retainer, on the other hand, is projected to cost in the neighborhood of $2,000, and involves none of the risks of surgery.

It turns out that the device itself might be the easiest part of the system to assemble. The real trick is to determine where to position the electrodes so that they will match up with the most sensitive areas of the tongue to deliver the clearest and most detectable signals. There has not previously been a significant amount of research into the patterns of nerves in the tongue, and it’s not completely clear that they are consistent from person to person. If the receptor pattern had to be customizable for each user, the device costs could increase considerably, along with fitting and training.

But if our receptor patterns are standardized to some degree, the process of manufacturing and fitting out the devices might be remarkably easy and inexpensive—a new option for hearing-impaired persons looking for assistive devices.

Watch this video from the team for more information:

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