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Robotic sounds after activation and why?

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I came across this article in a group on FB. It’s written by Dr Chad Ruffin, a CI surgeon and a bilateral CI recipient. It explains why we recipients have these robotic sounds after activation. It an extremely interesting read and to understand why this happens.

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Thank you for this. It is so hard to explain to others what we are hearing (experiencing). This article does a good attempt at that. The only thing I have issue with is the author continually references “low resolution hearing”. I disagree with this analogy. The uses microphones and electricity to stimulate the hearing nerve. This has nothing to do with normal or low resolution hearing. This is totally different hearing. Normal hearing is mechanical in nature using air waves, bones, and fluids to move hair cells (sensory receptors). With the CI all of this is overridden, and electricity is sent directly to the nerve. This stimulates our brain. I don’t think the brain knows what is happening at first, but eventfully try’s to make sense of the signals. If we are lucky, them our brains eventually use the electrical signals to create a new (similar) type of sound. I don’t believe it is a fidelity issue, but more of a brain plasticity issue.

@DWol999 said:

The only thing I have issue with is the author continually references “low resolution hearing”.

I think there is no question that hearing is low resolution. The normal cochlear has tons more nerve fibres detecting many more individual frequencies than the 22 electrodes (or whatever, depending on the brand) that a CI has. That is, the CI recipient can only detect 22 (or whatever) different “frequencies”, and it is the combination of these at different relative intensities and durations that is interpreted to make what is perceived as sound.

This would be the equivalent of our eyes only seeing the world broken up into 22 large pixels. Each pixel can be a different colour and brightness, and the combination of these might give you a clue that the person in front of you has waved but it would take a while for you to learn the colour combination that reflects this.

Reading about other people including myself about and robotic sound I have found it to be very different with different people. Some people have very little robotic issues and others have it bad.

Getting new mappings can improve or even make the robotic sound worse. Proper placement of the electrode is critical for the implanted for best sound quality. I have attached an article that I believe goes along with the OP’s article about sound quality of our implants.

The low resolution hearing got my attention.
I think it has a lot to do with people having difficulty with music for a while.

It’s something how everyone is so different about hearing.

Rick I agree with you about low resolution and music satisfaction. Music is truly a hard gig to enjoy without cringing af the horrid sound.

I am going to try to explain my issue with the comparison for “low resolution”. Please excuse me if this seems unnecessary, or long winded but to me there is a difference.

First off, the comparison of 16,000 hair cells to 22 electrodes is not correct. Yes, there are 16,000 hair cells but only 4000 of them are used for true sound. Additionally, the 22 electrodes use a completely different method to broadcast sound signal. This is done using direct electrical stimulus vs fluid motion and detection of the hair cells.

I will use the analogy of a prosthetic leg to demonstrate my point. When a person receives a prosthetic leg, they have a chunk of plastic and steal which can be attached to their hip. It in no way looks, feels, or acts like a real leg. This is the same as the . It is a prosthetic. The idea that a person can compare the “fidelity” of a functioning ear to a replaced one is not correct. If it were, then we would not need to train the brain to hear. Low fidelity can be heard and understood right away from a functioning ear and does not need training.

We receive an alternate form of stimulus with the CI and it has nothing to do with our natural biology. If we are lucky, and are brains are placid enough, then most can interpret the electrical signals as a sound replacement. All of this happens within the brain and is part of how we naturally interact with the world.

The comparison to the human eye “This would be the equivalent of our eyes only seeing the world broken up into 22 large pixels “, is also not correct. The retina of the human eye has about 127 million photoreceptors — rods and cones — to process visual signals. And there is no way to replace this function today. There is no CI for the eye. If there were, it also would be a very different way to “see”. Who knows what the brain would put together from an electrical signal? It might be an ambiguous blob resembling space relations to objects… It might more closely resemble radar or sonar images…
More details on the inner ear function:

Tuning in to the inner ear15

Basile Tarchini, Ph.D., is working to understand the basic mechanisms underlying hair cell development, with the goal of restoring hearing following injury.

Kind regards,
Dave

Hi Dave, it sounds as if we’re saying exactly the same thing but using different terms. Regardless of whether the method to get sound to the brain is via electrical stimulation or via hair cells, it all ends up as electrical impulses along the neural pathways anyway. In each of the examples (hearing, seeing, walking), the prosthesis attempts to approximate the natural method in some way or other but fails to even come close. That’s what I mean by low resolution or low fidelity. It’s just nowhere near as fine or precise as the natural system.

In reply to @DWol999

I’m always game for quibbling about semantics. :smiley:

@DWol999 said:

Yes, there are 16,000 hair cells but only 4000 of them are used for true sound. Additionally, the 22 electrodes use a completely different method to broadcast sound signal.

Hm. But I don’t think we’re really talking about the hair cells. Regardless of whether the input to the auditory nerve is from the hair cell or from the electrical signal from the implant, the output of the auditory nerve is good old electrochemical–the same type of signal it has always been. There are about 30,000 fibers in the auditory nerve that are traditionally activated by very specific input from the hair cells. With the implant, they are being activated by a local electrical impulse that is much less specific. Lower resolution actually seems like a pretty good analogy to me. But yes, the brain does learn to interpret this new (lower fidelity) code that it is getting, which requires learning. So it’s both. I’d also suggest that while it is lower fidelity it is not just 22 (or whatever the array is), because the brain will manage to interpret the different electrical gradients between electrodes.

The visual cortex is actually easier than the auditory cortex in a lot of ways (though not, in other ways), and because of its the regular mapping we are trying to just stick electrode arrays into the surface of the visual cortex to restore functional vision. I’d have to dig into why we’re jumping to the brain and can’t stimulate the optic nerve the way to do the cochlear nerve, though I’m sure we’ve tried. Off the top of my head, I would guess that the layout of the cochlear nerve endings in the linear, spiral, tonotopic cochlea* gives us a way of localizing the electrodes that the eye just doesn’t offer us. The corollary would be to place a sheet of electrodes basically over top of the retina itself, and I’m not sure that’s something we can physically. . . op, no, nevermind, we are apparently trying to do that, too. :slight_smile:

There’s also some interesting work out there in trying to restore vision with electrode pads on the back or on the tongue. Now THAT is a different input requiring dramatic brain plasticity.

*I’m reminded of that guy who was on the forum a little while ago pumping his theories that the cochlear is NOT tonotopic and that his better theory of cochlear mapping supported a better method of fitting hearing aids. From the angle of cochlear implants, that really does seem like a hard sell.

To add a little point that I think is maybe obvious but also relevant and worth keeping in mind: Auditory perception doesn’t actually happen in the ear (cochlea). It happens up in the brain.

Edited

Hi!
Thank you for reading my article–@Deaf_piper, cochlear implants are indeed low resolution hearing. If they were high resolution, you’d be able to hear in music and speech in noise at rates of typical hearing people. There are many factors that play a role in this–the cochlea has 3500 hair cells that detect sound. A cochlear implant at most has 20ish electrodes. Electrical hearing is FAR different than acoustic hearing. The key concept is thinking of information transfer with electrical hearing as water flow in a pipe. There is much more information that can be transferred with acoustic hearing–a large pipe, so to speak. Electrical hearing is useful, but carries nowhere near the amount of information. It’s just the way the nerve works. You hear two ways–with place, where the cochlear implant electrode is located and timing. In typical hearing, the auditory nerve fires at the rate of the frequency of sound. This provides the timing cue. With electrical hearing, the place is “smudged” because electrical current spreads. But few patients realize that the timing is waaaaay off. Electrically stimulated auditory nerves don’t fire to the frequency of the incoming sound. So you lose this HUGE cue for deriving the frequency of incoming sound.

That’s the short version. People dedicate their lives to these issues! Hope this is helpful!

It’s certainly an argument against people with normal hearing getting a cochlear implant. But it still provides superior hearing to someone with a sufficiently damaged system.

It’s a fascinating question to me. I had a evaluation last year and the result was ‘borderline’ (the worst result possible). I think if I had said I wanted one, they would not have objected. While I accept that my hearing will decline and- barring some unexpected medical breakthrough- I will be getting implanted at some point in the not-too-distant future, I do wonder.

To go through the surgery, the rehab, the mappings and at the end of it all have low-resolution hearing. To not hear my kids’ voices in their full musical glory. The audi that referred me for assessment was very upbeat about CI, and seems to think that really I just need some time to accept the inevitable. Maybe she’s right, but I’m not there yet. For the guys who spoke at the information session I went to, it was an easy decision. Their hearing had just reached that point. It’s a tough call for me.

When I read the article it almost upset me. I thought who is this guy that probably has normal hearing bad mouthing . He really doesn’t understand what CI is about

When a person’s hearing gets bad enough and that person wants to communicate with family and friends and possibly hold a good job, CI is wonderful.

The article compares CI hearing to normal hearing, says it’s low resolution at best. What is normal? With hearing loss normal is always changing. Our brains adapt to make a new normal.

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