Neuroscience take on Human Hearing,...author is Frank Amthor - Page 1
Forum section: electronics / general

author: RJSV
author_rank: Super Contributor
timestamp: October 30, 2022, 10:16:05 pm
content: Hey hey!Been reading about human hearing frequency response, and author Frank Amthor puts together a compelling narrative!Apparently, (my own summary), the human ear can really only reach up to about 1 to 2 khz, but 'required' to function at detecting frequencies somewhat higher;In a nutshell, the human neurological system design does 'skipping', where a 4 khz auditory signal is tracked every-other cycle. Then, along same lines, a 7 khz signal gets tracked, and detected, at a 1 of 3 hit ratio, that way the inner ear gets a re-constructed range or 'dial' scale of audible frequencies from 1 khz through 10 khz...(Many of us don't hear above about 4 khz).Book author Frank Amthor 'Neuroscience for dummies' (Wiley books), takes detail to explain some extra physical characteristics such as hair and shaping of outer ear as a sound director, but more subtle is the frequency shaping / response.

author: jmelson
author_rank: Super Contributor
timestamp: October 31, 2022, 03:57:49 pm
content: I think this is confusing time response with frequency response. You can hear much higher frequencies than 2 KHz because the cochlea causes standing waves, where the nodes tickle hair cells at specific spots. The time response is how fast you can detect the starting and stopping of a specific frequency. If a 10 KHz tone is chopped on and off at a 1 KHz rate, you will hear it as a distorted 10 KHz pitch, but you won't be able to detect what the chopping frequency is.Jon

author: RJSV
author_rank: Super Contributor
timestamp: November 01, 2022, 08:16:49 am
content: Thanks, I don't have extensive exp with acoustics, but was expressing amazement, that human nervous system 'signals' rate...or bit-rate equivalent, is limited to about one or two milli-seconds. Apparently, there is a switch-over, from directly 'tracking' the sound pressure wave, to directly tracking ever-other (book said in discrete multiples), with several ranges going up the frequency scale.The mention of standing waves, I've not heard about but might be part of the response. It did mention, that the higher frequencies get the first or front little portion of the hairs and cochlea resonating to shortest wavelengths, with neurological response by stimulation, directly producing proportionally or fully tracking something like a 800 hz sound.(Edit) The arrival of lower frequencies causes a deeper involvement into the cohlea, due to wavelength, those can (edited) be 'tracked' at base-rate. The brain-cohlea system still works, I think (my reading) maybe you could state, that the inner ear CAN track higher frequencies, 'accoustically' but can't generate the electric response fully, nor transfer at rates faster than with periods below about 500 uSec...and that limit also is present for Visual conversion, to inner brain signals.That is what I've found fascinating; that a sort-of 'skip' tracking would have to be happening way after any ear involvement, and there maybe is similar 'edge-detect' differentiation happening, way separate physically, (from either the ear, in the hearing function case, but also from the eye organ, in the vision case.Anyway, thanks for mentioning the standing waves, but also I wonder; about a hearing detection mechanism, when audio is so high up the (human) range that the person is really only able to perceive that 'some sound', a 'hiss' of some kind is happening, but without pitch clues, way up past 10 khz.

author: jmelson
author_rank: Super Contributor
timestamp: November 01, 2022, 04:15:08 pm
content: I don't believe any of this. A LONG time ago, psychophysiologists thought that animals detected the location of a sound from differences in amplitude at the two ears. Current wisdom of the time was that different arrival time of the signal was way too short for neurons to process that. Then, they did studies on cats that showed the auditory processing WAS fast enough to resolve VERY short differences in arrival time to the two ears. But, what you are describing (I have not read the reference) seems to indicate the ear does sense each wave of an incoming sound and uses an anti-aliasing technique to detect frequency. My understanding is the incoming sound waves produce standing waves in the cochlea, and these waves stimulate hair cells along the length of the cochlea, where their position is correlated with frequency. So, the standing waves separate out different frequencies, and the hair cells respond with the time-varying part of the signal. I have been very protective of my hearing, and have been able to preserve a fair bit of my higher frequency sensing. (I'm going to be 72 next week.) Many years ago I could easily hear the ~15,750 Hz horizontal sweep frequency of TV sets (back when they had flyback transformers). I just checked with good-quality Sony headphones and was a bit disappointed to find out that my hearing falls off the cliff at around 11 KHz.Jon

author: RJSV
author_rank: Super Contributor
timestamp: November 01, 2022, 06:34:52 pm
content: Thanks for questions. I've gotten the details, from page 122, for example. Please also see:2nd. Edition 2016 Neuroscience for Dummies, by Frank Amthor...published by John Wiley and Sons, Inc.I've been looking at this because of information of similar nature (I.E. retina / brain 'rates' equivalent 'bit rate' capacity is low). The YouTube presentations, by Shanhui Fan that I've been viewing discusses that 'information Transfer' rate issue in regards to optical / visual processes.Please read, some arguments follow:The book is mentioning having nervous pathways finely tuned, in length and thus finely resolved timing differences are present (in the structure) where nerve firing pairs can detect the simultaneous quality, ultimately being the audible 'paths' taken to each ear.So, I think he is saying you might not be able to track the signals fast enough, but you can get a signal indicating 'simultaneous' arrival. Repeating that, for clarity, that means the sound wave path (lengths) are different, but then delayed precisely, by nerve path lengths, to have that detection window.Of course, there are many of these 'pairs' for the sensing of horizontal direction.Also, although I'm not so much interested in amplitude info being used, by the two ears for direction (azimuth or horizontal angle), but the system uses amplitude difference cues as well, apparently.My main interest here, is the simple fact that, in spite of limitations, of continuous tracking detection, the sensing system tracks sound mechanically, but tracking is still accomplished,...just not continuous, with the audio waveforms. The spiral cochlea tracks the fast stuff, like 6 khz, but the nerve functions DON'T track in a continuous manner.Ditto for visual functions, I'm thinking.Another fascinating aspect, regarding 'data rate' equivalents is mentioned, in that chapter 6 (The Auditory System) is the lack of natural mapping, that the hearing system has, whereas the visual system naturally can map a coorelation between eyeball muscle positioning, and retina response to the different directions...that's two different elements that will be mapped in coordinated function. Thus infants have a natural correlated situation.Other than that book, I'm using Professor Fan's video lecture, for the info, on Visual info transfer speeds or speed equivalents (bit-rate as Prof Fan liked to analogy).Please see also:YouTube Shanhui Fan 'Collequim' lecture.

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 01, 2022, 07:22:14 pm
content: Of course, this is still simplified. But we have known for several decades now that groups of neurons are able to process stimuli at a much higher rate than each individual neuron can. Otherwise, given the relatively slow reaction of typical neurons, our nervous system would be hopeless.And again, probably oversimplifying, it all works pretty much the same way as "sampling oscilloscopes" do, which are able to acquire high-freq signals with low-sample rate ADCs.