This is audio related and should be of interest to us all. I found it educational but not technical. Hope you find it interesting as well.
I am not sure who to credit as the author but he is well versed on this subject I think it may be Douglas
Hofsteader who is quoted herein.
Hearing is not the same as listening
Did you hear what I heard? You'll never know. Our experience of the music we listen to is shaped by extensive processing of the raw vibrations that enter our ears. That processing, by the auditive and cognitive centers of our brain, is itself strongly shaped by a long trail of experiences, expectations and culture. Plus another dozen or more factors.
Most people are not so much interested in the mechanisms (both physically and mentally) behind listening. But listening is really where it all comes together. The enjoyment of music, the interpretation of performances, the judgment of audio reproduction quality is not done with our ears. It is done within our brain. The ears are the sensors that provide our brains with just a physical sample of the air vibrations that represent the sound. What those vibration mean, what they signify, and their quality is determined by the brain.
In his latest book "I am a strange loop", Douglas Hofstadter says it as follows:
"The passage leading from vast numbers of received signals to a handful of triggered symbols is a kind of funneling process in which initial input signals are manipulated or "massaged", the results of which selectively trigger further (i.e., more "internal") signals, and so forth. This baton-passing by squads of signals traces out an ever-narrowing pathway in the brain, which winds up triggering a small set of symbols whose identities are of course a subtle function of the original input signals.[...] In the interest of clarity, I have painted too simple a picture of the process of perception, for in reality, there is a great deal of two-way flow.
Signals don't propagate solely from the outside inwards, towards symbols; expectations from past experiences simultaneously give rise to signals propagating outwards from certain symbols. There takes place a kind of negotiation between inward-bound and outward-bound signals, and the result is the locking-in of a pathway connecting raw input to symbolic interpretation."
The brain does NOT take the ears at face value
And in case you are wondering, the brain does NOT take the ears input at face value. It is as if the brain says: OK, ears, I get that, but let me look at a couple of other inputs as well. What mood am I in really? How does that equipment actually look? Color, size, cost? Did I build it, or did I lay out hard-earned money to buy it? Or is it from a manufacturer I heard bad things about? Etcetera, etcetera.
How DO you become aware of what you hear? I mean, it's not as if you 'feel' those vibrating hairs in your inner ear and think, aha, that's a piano! No, somehow, the brain makes you 'aware' that you hear a piano. Pretty mysterious, that whole process. But scientific research has come a long way to unravel at least some of it...
A landscape of sound.
Imagine that the brain has many areas that react to a certain input. There is an area that mainly acts on sound, one that mainly acts on colors, one that mainly acts on how you feel (what Antonio Damasio calls 'the body state')
The important word here is 'mainly'. Because, there is extensive interconnection between those area's, there is an exchange of information to built your perception. Call it a landscape of neuronal activity, all over your brain, that couples and integrates all those inputs (external and the internal body state) and which leads to a particular state of 'perceiving' the world around you, sound, sights, emotional state, etc. A nice example, related to the total integration of sensory inputs to the perception of audio, is described by Floyd O'Toole, VP of Acoustical Engineering at Harman, in an article called Audio science in the service of Art. The article is quite long to download, but this excerpt makes this particular point.
So, we are unknowingly building, revising, redoing that perception landscape while we go about our business. But the actual vibrations of those hairs in your inner ears are only ONE input of many others. That particular vibration information gets integrated in the total picture. But unavoidably, in that process, much of it is thrown away. The brain uses this, discards that.
Now, if you are trying to listen attentively to a particular sound, the 'gain' of the sound area is turned up and that of the other areas is turned down. You can be so immersed in listening that you hardly know what's going on around you. You can tune the attention of your brain. In fact, that gain can be turned up so high that you think your hear a sound that isn't there. You can create a certain landscape in your brain that is totally imaginary.
Just making it up
Lets taken an example from vision because vision experiences are much easier to discuss. Focus your attention on your mother's face. Got that? OK. Now, I assume your mother is not right there with you (if so, try your father's face). Do you realize what is going on? You 'see' something that isn't there, that is constructed by your brain from memories. A figment of your imagination if there ever was one.
Now, very likely you also have a particular emotional feeling, connected to your mother. You may remember a nice meal she cooked, or you remember her serious illness last year, or you feel guilty because you haven't called her lately. All constructs from your brain, created without physical perception inputs.
It's even worse. If indeed you remember that nice meal, you probably 'see' how she smiled at that occasion when you complimented her. Or, if you remember the sickness, you probably 'see' her as a sick person. If it was a serious sickness, chances are that you actually 'feel' bad. Not only does the brain create a perception all by itself, it also selectively 'shapes' that creation depending on which memory you happen to access and it influences your 'body state' to match the perception. When you imagine a bad situation, your body also starts to 'feel bad'.