Posts tagged with cochlear implants

Bionic Man Update

On the cochlear implant front: they now have ability to pipe audio wirelessly into your brain if you have a cochlear impant, using “hearing loops”.

Traditionally, hearing aids are available with “T-coil compatibility”, which allows certain things, like compatible telephones, to electromagnetically couple with the electronics in the hearing aid, rather than taking the tiny, noisy audio signal from a phone speaker, sending it through an airgap polluted with ambient noise, and into a microphone, and then into the headphone’s circuitry. The idea is there’s a voicecoil in the speaker anyway, and an EM field is driving it, why not pick up the electromagnetic flux in the hearing aid with a loop of wire and feed that to the amplification circuitry?

This has been expanded so that a loop of wire can be strung around a room, and an audio signal can be run through it, and then it will couple with your hearing aid and you hear it.

Naturally, they’ve made cochlear implants compatible as well. In concert halls, they will send the mix into the hearing loop. In London, black cabs have tiny microphones embedded in the dashboard, and transmitting hearing loops in the back of the cab. You can go see a performance of Wicked in New York, and the SR guys run a separate mix to the hearing loop, and if you have a cochlear implant with the T-coil mode, the EMF audio signal will go directly into your brain, no old-fashioned vibrating air necessary.

This also means, if you are Deaf, but you play the electric guitar, say, you don’t really need practice amps. You should be able to electrically hook the guitar up to your cochlea. You can buy hearing loops shaped to hang onto your ears like sunglasses, with minijack connectors for your laptop or your iPod.

There are some unsurprising problems: inductance losses roll off high frequencies (just like in any long run of audio-frequency signals through an unbalanced cable), there is limited dynamic range (more specifically, many people with severe hearing loss and the current technological remedies we have for that loss have very limited dynamic range, and so the signal must be kept within that range to avoid unpleasant artifacts). But Richard Einhorn was just on the radio saying it sounded great.

If I understand how this works, any changing electromagnetic field that’s strong enough and within the frequency range of the cochlear implant should come through into your auditory nerves, when T-coil mode is turned on. This is almost like having another sense. People with cochlear implants should be able to “hear” certain EM fields. If you walk past a huge motor, or a prime mover in a power generation facility, you should hear the deep thrum of the field thrown off by the spinning armature. In fact, the pitch would depend on how many arms the armature has, right? In multiples of the rotational frequency. You could tell something about the motor design from the octave of the “sound”.

It is entirely possible that I don’t understand this right, but I just can’t get over the fact that not only do there exist machines that wirelessly transmit audio signals directly into your brain, but that they are already commonplace. They’re in cabs. They’re installed in 18,000 post offices in the UK. The most fundamental thing about the experience of sound, that it is a vibration of air or other medium, that animals developed to sense goings-on in their environment, is now optional. It is now totally possible to electronically hijack the neural circuitry behind this purely for the exchange of cultural information like cab fares and Wizard of Oz musicals and TED talk podcasts, and to skip the whole “vibrating air” thing entirely.

( via Richard Einhorn on NPR)

We Have The Technology

How amazing is this video of a little baby getting his cochlear implant switched on? Also how amazing is the “YouTube : cochlear implant videos :: photography : hearing aid pictures”analogy? I saw this on Reddit this morning. There are dozens of these videos on YouTube (like this one).

Along with the controversy in the Deaf community, another issue with cochlear implants is that while they allow their users to understand speech and hear other environmental cues like doorbells and car horns, they don’t completely restore what we would generally think of as “hearing,” per se. The way the devices work is pretty simple: take an audio signal from a microphone, feed it to a filterbank with somewhere on the order of 8–20 bands. Take the levels from the filterbank’s outputs and map them to electrodes inserted into the cochlea, and hope the brain can reapply the tonotopic mapping in the cochlea to the pattern of stimulation from the electrodes.

This is essentially what the front half of a vocoder does. Not T-Pain’s Auto-Tune with retune speed set to zero that everyone calls “vocoding,” I’m talking about Roger Troutman and Zapp, California Love, Kraftwerk-style. Instead of using the vocoder front end to drive a filterbank hooked up to a keyboard or something, cochlear implants plug that part straight into the brain. It’s futuristic in a disco way.

Consequently, a cochlear implant does not let its user hear music, at least not in any way like what the hearing community would consider to be listening to music. When you hear Roger Troutman sing I Want To Be Your Man, all the pitch information is coming from the keyboards. The filtering, the harmonic structure of “Wanna Be Yooouuuur MaaAaaAn” comes from his voice and the vocoder, but it tosses out the pitch information, and the keyboard brings it back (which is why it sounds similar to Auto-Tune: the pitch is locked perfectly and has instaneous jumps with no gliss or portamento, because it’s a keyboard. Just like Auto-Tune when the retune speed is zero). This isn’t exactly how the cochlear implant works, but it’s similar.

The processing strategy is a main block upon which one has to choose the implant manufacturer, research shows that patients can understand speech with as at least 4 electrodes, but the obstacle is in music perception, where it returns that fine structure stimulation is an important issue. Some strategies used in Advanced Bionics and Medel strategies make use of fine structure presentation by implementing the Hilbert Transform in the signal processing path, while ACE strategies depends mainly on the Short Time Fourier Transform.

Ignoring for a second how not up to Wikipedia’s quality standards this bit is, how awesome is it that people are even working on this? “What? The electronic device you implanted in that child’s brain allows them to hear speech, ambient environmental sounds, and all the other auditory cues necessary for success in human society but NOT MUSIC? DID YOU TRY THE HILBERT TRANSFORM?” If I was a newspaper editor and I had to hed this story I’d go with “HUMANS: NOT TOTALLY SHITTY?”

(Further reading: a 2005 Wired article by a guy with a cochlear implant trying to improve its performance on music.)