The most obvious way to give sight to blind and hearing to deaf is to give them a replacement organ for these. In order to do that we would need to understand how our eyes and ears encode sensory information into electrical signals which then go into the brain. My question is, how close are to understand this mechanism at this time?
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$\begingroup$ I don't understand your question -- My confusion is reflected in the responses to your post; Bryan Krause's quite excellent comment below delves into implant world, while some answers allude to normal physiology. I think this is because the post's body and title don't match -- they reflect the ambiguity in the question. In other words, like Bryan suggests -- current prosthetics don't treat hearing loss or blindness by reproducing normal physiological processes. $\endgroup$– AliceD ♦Aug 26, 2020 at 19:17
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$\begingroup$ See what I want to know is, do we understand exactly how the vision is converted into electrical signals and how to interpret those signals? I am an electronic engineer myself and have studied a few communication protocols. My question arose during my contemplation of how we encode information in electronic systems. $\endgroup$– gyuunyuuAug 27, 2020 at 9:42
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$\begingroup$ Well, do we know it 'exactly'... no. But we do know a lot. But the visual system is large and complex. From physical stimulus to 'interpretation', as you say you wish to learn, is a lot to ask for. It spans the full range from sensation to perception to association - impossible to capture in a single answer. Dependent on your background knowledge, it may take a full uni course to even just understand the very basics I reckon. $\endgroup$– AliceD ♦Aug 27, 2020 at 9:53
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$\begingroup$ I am only curious to know to what extent we can create an artificial eye that behaves like the real one at the present time $\endgroup$– gyuunyuuAug 27, 2020 at 12:36
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$\begingroup$ That answer to that Q is very simple - we can't :) Bryan has abstracted that below. I've worked with folks with retinal implants - while promising, it's not even close to normal vision. $\endgroup$– AliceD ♦Aug 27, 2020 at 12:51
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2 Answers
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I think the encoding is quite well understood, and in fact there are artifical cochleas available for deaf people: https://en.wikipedia.org/wiki/Cochlear_implant
For retina replacements, I think the hurdle is establishing the connections from any device to the nerve. There are roughly 120 million rods and 6 million cones in the human eye. (Per Wikipedia: https://en.wikipedia.org/wiki/Photoreceptor_cell ) These connect to about 1.2 million optic nerves, so making the proper connections would seem to be a non-trivial matter.
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1$\begingroup$ Cochlear implants work by stimulating the nerves that normally innervate the hair cells. They give very low resolution - only about 20 total sites over the entire frequency spectrum. It would be just as much a hurdle to connect to the 30,000 auditory nerve fibers. However, there is enough redundancy in speech that the 30,000 -> 20 mapping is enough to resolve some speech from one talker (some other cues for direction and resolving multiple talkers are much more difficult). You can do the same thing in the retina, the problem is that you don't get much useful vision out of that low resolution. $\endgroup$– Bryan Krause ♦Aug 26, 2020 at 17:14
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$\begingroup$ See also: en.wikipedia.org/wiki/Visual_prosthesis $\endgroup$– Bryan Krause ♦Aug 26, 2020 at 17:15
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$\begingroup$ @Bryan Krause: I'd disagree that it's just as much of a hurdle. 20 into 30,000 nerves is rather easier than 20 into a million. The problem is that hearing is linear, while sight is two dimensional, so for equivalent resolution you need to square the number of sensors/connections. $\endgroup$– jamesqfAug 26, 2020 at 22:56
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$\begingroup$ Even 20x20 pixels isn't much. It's less about 2D and more about temporal vs spatial resolution; it's a lot easier to put temporal information into one channel than it is for spatial. Paul Bach-y-Rita did make a tongue stimulation device for vision ( en.wikipedia.org/wiki/Brainport ) that gives about that 20x20 resolution. It's enough to help not bump into stuff but you aren't going to read. The rest of the information is conveyed with pre-processing rather than trying to render an actual image. $\endgroup$– Bryan Krause ♦Aug 26, 2020 at 23:14
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In general I would say a lot is known:
Seeing starts with the photo-receptors. See "signal transduction" section of the Wiki: Signal transduction works though rhodopsin and subsequent closing and opening of ion channels.
Then the signal is transferred from the optic nerve to the brain.
Hearing works though hair cells and mechanotransduction.
