my understanding of some auditory neurobiology
Although I enjoy much of the content on this forum, and follow the back and forth on this thread, I am usually able to resist the urge to comment. But there have been a few things over the past few days that I cannot resist the urge to pass on my understanding of some issues related to recent posts. I hope that these comments are taken as I intend, which is to help inform some of you on subjects that may be improperly or incompletely understood.
I am an EE, but for about the last two decades have worked in the field of neuromodulation so I have had the opportunity to learn something about how our bodies function. Some of this work has been directly related to our sense of hearing.
This is mostly correct, but there is one error that should be clarified for everyone. There is essentially no amplitude modulation in the nervous system. It is a pulse rate modulated signal. If you understand how an action potential is propagated along an axon, you will understand why this must be the case. You cannot have a high or low amplitude nerve pulse, only a higher or lower rate of nerve impulses.
On another subject, mm has discussed the auditory nerve and the auditory cortex. This is not a direct connection. The auditory nerve connects to the medulla, which connects to the pons, which connects to the midbrain, which connects to the medial geniculate nucleus, which then connects to the primary auditory cortex. There is processing that occurs at each of these locations, but the only one that is believed to be related to consciousness is the last. Interconnections between the left and right side occur at the first three, and are related to timing processing. For example, the automatic function of turning your head to a sharp new sound is believed to occur in the midbrain. And the tonotopic mapping that occurs in the cochlea is maintained throughout these different parts of the brain. There is no mapping related to amplitude, only frequency.
One final subject for the night is that although the electronics and transducers used for audio reproduction are, for the most part, time invariant, our body’s auditory systems are clearly not so. There are several parts where this has clearly been shown. For example, any particular auditory nerve will fire occasionally in the absence of any stimulus. If you stimulate that nerve with an appropriate frequency burst, when the burst ends that nerve will produce no impulses for some period of time.
This is my understanding from what people have taken the time to teach me, as well as a couple of thick textbooks. But of course that doesn’t mean you should take my word as absolute fact, I could be wrong, or the science could be revised in the future. After all I believe that science is a walk along the path to greater truth, not a destination.
Brian
Although I enjoy much of the content on this forum, and follow the back and forth on this thread, I am usually able to resist the urge to comment. But there have been a few things over the past few days that I cannot resist the urge to pass on my understanding of some issues related to recent posts. I hope that these comments are taken as I intend, which is to help inform some of you on subjects that may be improperly or incompletely understood.
I am an EE, but for about the last two decades have worked in the field of neuromodulation so I have had the opportunity to learn something about how our bodies function. Some of this work has been directly related to our sense of hearing.
This is mostly correct, but there is one error that should be clarified for everyone. There is essentially no amplitude modulation in the nervous system. It is a pulse rate modulated signal. If you understand how an action potential is propagated along an axon, you will understand why this must be the case. You cannot have a high or low amplitude nerve pulse, only a higher or lower rate of nerve impulses.
On another subject, mm has discussed the auditory nerve and the auditory cortex. This is not a direct connection. The auditory nerve connects to the medulla, which connects to the pons, which connects to the midbrain, which connects to the medial geniculate nucleus, which then connects to the primary auditory cortex. There is processing that occurs at each of these locations, but the only one that is believed to be related to consciousness is the last. Interconnections between the left and right side occur at the first three, and are related to timing processing. For example, the automatic function of turning your head to a sharp new sound is believed to occur in the midbrain. And the tonotopic mapping that occurs in the cochlea is maintained throughout these different parts of the brain. There is no mapping related to amplitude, only frequency.
One final subject for the night is that although the electronics and transducers used for audio reproduction are, for the most part, time invariant, our body’s auditory systems are clearly not so. There are several parts where this has clearly been shown. For example, any particular auditory nerve will fire occasionally in the absence of any stimulus. If you stimulate that nerve with an appropriate frequency burst, when the burst ends that nerve will produce no impulses for some period of time.
This is my understanding from what people have taken the time to teach me, as well as a couple of thick textbooks. But of course that doesn’t mean you should take my word as absolute fact, I could be wrong, or the science could be revised in the future. After all I believe that science is a walk along the path to greater truth, not a destination.
Brian
Thank you for your mountain air clarity of thought, I can now see for miles. ToS
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Great post, Brian - thank you
It's unusual to find someone who can straddle & has expertise in both EE & neuromodulation (a very interesting field, if I understand correctly what it is - "the alteration of nerve activity through targeted delivery of a stimulus, such as electrical stimulation or chemical agents, to specific neurological sites in the body". (from wikipedia)
Just a question about amplitude mapping - I presumed how amplitude was represented in this nerve conducting schema was that the number of nerves firing determined the amplitude even though each nerve can only assume a binary on/off state?
Just one other thought about amplitude - amplitude modulation plays such a significant role in nature that it would be unusual for our auditory system not to have addressed it. I believe amplitude modulation filters are thought to be a primary mechanism in auditory perception - any thoughts on this?
What you might also be referring to are otoacoustic emissions where the cochlea actually emits its own sounds spontaneously?
Thank you, again & I completely agree that science is a journey, not a destination - I would go so far as to say that if we think we have arrived we are no longer thinking in a truly scientific way.
It's unusual to find someone who can straddle & has expertise in both EE & neuromodulation (a very interesting field, if I understand correctly what it is - "the alteration of nerve activity through targeted delivery of a stimulus, such as electrical stimulation or chemical agents, to specific neurological sites in the body". (from wikipedia)
Excellent & thanks for sharing
My simplistic understanding (I may over-simplify so please correct if my simplification is misleading) is that nerve cells work somewhat like a schmitt trigger - being an electro-chemical system, the neurotransmitter chemical (acteylcholine) has to reach a certain level in the synpatic gap between one nerve & the next before the next nerve fires. So it's an all or nothing transmission - same as schmitt triggers in EE, if I understand them correctly? Being a electro-chemical system it has to have a recovery time for neurotrnsmitters to be synthesised & also it directly relate sto the time-variance you mention below.
Again, thanks for elucidating this. I was aware that there were many intermediate stages between ear & auditory cortex (but would not be able to name them off the top of my head) & thanks for outlining that they each have a processing role & that the tonotopic mapping is maintained throughout the journey from basilar membrane to auditory cortex.
Just a question about amplitude mapping - I presumed how amplitude was represented in this nerve conducting schema was that the number of nerves firing determined the amplitude even though each nerve can only assume a binary on/off state?
Just one other thought about amplitude - amplitude modulation plays such a significant role in nature that it would be unusual for our auditory system not to have addressed it. I believe amplitude modulation filters are thought to be a primary mechanism in auditory perception - any thoughts on this?
Being electrochemical both saturation & depletion of the neurotransmitter chemical are possible - listening to a tone for a period diminishes the evoked nerve potential, AFAIK. A simpler more direct example might be - in vision staring fixedly at an object & then closing our eyes we still see the imprint of that image for a while.
What you might also be referring to are otoacoustic emissions where the cochlea actually emits its own sounds spontaneously?
Thank you, again & I completely agree that science is a journey, not a destination - I would go so far as to say that if we think we have arrived we are no longer thinking in a truly scientific way.
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Fripp & Eno's "No Pussyfooting" is great too...
Terry Riley's "A Rainbow in Curved Air" is an old favourite..
Oh, and early Tangerine Dream - Atem for example.
+1. And a lot good happens here, even in this thread. There have been some good discussions over the last months - and some lows, but that's to be expected. JN's thoughts on speakers springs to mind - and today's excellent post from BrianDIY.
Forums go up and down all the time - but like you I see plenty of good.
But I avoid twatter and facepalm like the plague!
I am a bit surprised that "quora answers" without citing any reference should be now considered as the ultimate book of knowledge.
I've cited already from the relevant literature which does not corrobate syn08's point of view for good reasons.
We are talking about LTI systems and the acronym means "L (inear) T (ime) I (nvariant)" and the "T ime I nvariant" already denotes the fact that the physical properties of the system do _not_ change.
Therefore the term "steady state" is not needed as denotation for this property of the systems we are examing.
For this reason the term "steady state" is used to describe the condition of a system, that has settled, after any excitation has taken place. And it is established with this meaning in control theory/EE for the last 40 - 60 years. (I did not look back farther).
I tend to think that there is the reason to find why "quora" was cited instead of any relevant literature from the field.
And of course it is always an approximation to use the term LTI as the systems we are talking about are usually in the category of "weakly non-linear" and "mainly time invariant" (sometimes even more than weakly non-linear)
I've cited already from the relevant literature which does not corrobate syn08's point of view for good reasons.
We are talking about LTI systems and the acronym means "L (inear) T (ime) I (nvariant)" and the "T ime I nvariant" already denotes the fact that the physical properties of the system do _not_ change.
Therefore the term "steady state" is not needed as denotation for this property of the systems we are examing.
For this reason the term "steady state" is used to describe the condition of a system, that has settled, after any excitation has taken place. And it is established with this meaning in control theory/EE for the last 40 - 60 years. (I did not look back farther).
I tend to think that there is the reason to find why "quora" was cited instead of any relevant literature from the field.
And of course it is always an approximation to use the term LTI as the systems we are talking about are usually in the category of "weakly non-linear" and "mainly time invariant" (sometimes even more than weakly non-linear)
Of course to both - but I'm a bit wondering why you cited my response to a very specific question from 00940 ?
These are different questions than the one I answered before....
As I' ve stated before, THD numbers are relevant and in the case of _zero_THD we don't need to worry about IMDs as there weren't any. (The basic distortion mechanism is always the same - means the nonlinear transfer function - but the excitation signals, and therefore the system's response, are diverging. If the transfer function is linear, it does not matter which waveform is used for the excitation, the response can't have any distortions if used within the limitations)
And of course it depends on the definition of the term "properly recorded" as for example "intersample overs" can excite the system more than a 20 kHz sine wave.
Otherwise it is true in a bandlimited system (digital) like the Red Bood CD, used with reasonable safety margins, the highest usable frequency is a 20 Khz sine wave and so a 20 kHz sine wave with FS level will provide the worst case.
Otoh, switching on a 20 kHz sine wave with FS level will provide an excitation far more demanding.......and would violate the limits of the Red Book CD system.
Recorded content with higher bandwidth but suffering from the same FS clipping will be more demanding.
Yes, I saw that & had to laugh - it's very telling how only a gossip site could be found to support Syn08 erroneous statements
Yes, IME audio systems are not quite LTI, this is why I have stated that ABAB is not identical to AABB and this is but one reason for ABX testing returning null results when testing for fine differences.
ABX testing procedures need to take this property/problem into account if results are to be regarded as valid.
Dan.
No. Well implemented 44.1/16 is able to reproduce 20kHz sine precisely.
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I’m not sure I would like Twitter, it sounds evil. I’ve been to Facebook a few times, it’s a bit like The Matrix - too much of the wrong information. Now that I feel accepted, I quite like diyAudio. These discussions are really helping my developmental work with sculptural sound. I just wish I had the intellectual capacity to directly understand what the heavy hitters are saying, and so my learning is mostly by osmosis.
BTW Chris719, I got my £9 Apple lightening headphone DAC the other day, and shall be giving a uniquely ToS writeup shortly.
ToS
PS: thought BrianDIY’s post on hearing was one of the best I have read in ages.
I've never even looked at Twatter, I don't know that anyone I know uses it, I know polytrixians use it, that's all I need to know.
I was friendly with someone who only wanted to communicate via FB, I gave it a go but very quickly decided to sacrifice the friendship.
The destination is the Grand Unification Theory and we are of course on a journey and far from achieving this goal, it seems that the ancients prior to Gobekli Tepe (12,000 years BCE) who were adept at quarrying stones weighing hundreds of tons and transporting them hundreds of kilometers knew more than we are allowed to believe/know at this point in time.
The Einstein Hoax - The Disastrous Intellectual War on Common Sense see - Conclusion P107.
Dan.
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Dan,
I have downloaded this and will be reading it with interest. There are lots of things that I trying to understand, especially the grand unification of my own diaspora of disparate thinking - and audio.
ToS
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