We all hear the same thing

A basic premise of this study is that the hearing system, up to the point where it delivers signals to the auditory cortex, is an automatic mechanism, and therefore all people with normal hearing receive the same sensations from the same sounds. It would appear to be amply supported by psychophysical testing with pure tones and by medical audiometry. It is also tacitly assumed in any discussion between two people who have heard the same piece of music; they may have observed different things and have reacted very differently, because those are cortical processes, but people do not commonly say ‘Well, I got a different sensation.’ If they did there would be no basis for criticism or review, or indeed for music itself. On such grounds it is legitimate to call the system up to the point of delivery a ‘machine’. But why our hearing behaves in this way has nothing to do with music or speech. We discovered there is reason towards the end of Chapter 10. Our sense of the direction from which sounds appear to arrive is absolutely dependent upon the faithfulness with which the detail of transients is supplied to our direction-finders. Our survival depended on it; we still have that ability in every respect. Natural selection determined how the ears should work, and it obtained the best possible machinery from the potential of the living material to achieve it. And that is why we now hear what we do hear in the form that we get the sensations. Those are also the grounds for suggesting that our hearing system has not changed for a hundred thousand years or more, and, since higher mammals who have excellent directional hearing have very similar anatomical structures, the reason for saying that it may not have changed since the emergence of mankind, a million or more years ago.

In addition to the nerves which carry the signals upwards from the ear to the cortex, there are nerves which run in the opposite direction as there are in most of our body's systems.