In order to regain their sense of hearing, many deaf people currently opt for cochlear implants. Such devices are expensive, however, plus they must be surgically installed and they don't work on all forms of hearing loss. That's why a group of researchers at Colorado State University (CSU) are developing an alternative – an electric retainer that transmits spoken words to the user by buzzing their tongue.

Cochlear implants start by utilizing one or more external microphones (located adjacent to the ear) to receive sounds. That audio is filtered through a speech processor, which picks out the sounds that are actually human speech. Those speech sounds are then converted into electrical impulses, which are transmitted through the user's skin to a series of electrodes implanted in the cochlea. Those electrodes in turn directly stimulate the user's auditory nerve, delivering sound information to the brain.

Being developed by a team led by Prof. John Williams, the CSU retainer works in a similar fashion, in that it also uses a microphone-equipped earpiece to pick up sounds which are then converted into electrical signals. In its case, however, those signals are then sent by Bluetooth to the retainer, which the user holds in their mouth. When they press their tongue up against the device, a series of electrodes in it respond to the received signals by selectively stimulating nerves in different parts of the tongue.

After a period of training, it is believed that users could learn to associate specific patterns of "tongue tingles" with given words. According to the university, "The tongue contains thousands of nerves and the region of the brain that interprets touch sensations from the tongue is capable of decoding complicated information." The scientists compare the system to Braille, in which blind people mentally convert bumps felt with their fingertips into written letters and words.

Unlike the case with cochlear implants, no surgery would be necessary in order to use the system. It should additionally be much less costly, plus it wouldn't require users to still have a functional auditory nerve.

More work still needs to be done before the device can see widespread use, however. For one thing, Williams and his team are still in the process of mapping out the nerves in the tongue, to determine which parts of the organ would be most receptive to stimulation.

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