The sense of hearing is an important precondition for communication and orientation, and it determines our emotions considerably. In contrast to our eyes, we cannot close our ears – we hear non-stop what happens around us. The human ear consists of the outer ear (earlobe and ear canal), the middle ear (including the bones of the middle ear, or 'ossicles'), and the inner ear (cochlea and semicircular canals, which provide for the sense of balance). 30.000 receptors (hair cells) in the inner ear react to the dissemination of minute pressure and density changes in elastic media (gases, fluids, solids).
They transform acoustic waves into electrical impulses and transmit these acoustic signals to the brain via the acoustic nerve. The shape of the ear canal causes resonance effects, which lead to an acoustic amplification of frequencies between 3000 and 4000 Hz. This is the frequency range in which human hearing is optimal and which is used for most of our spoken communication. The stapedius reflex protects our ear from sound levels above 80 to 100 dB: The muscles in the middle ear contract, limiting movement of the ossicles and hence transmission of vibrations to the inner ear. This protective reflex sets in quickly (about 50 ms after perception of the sound) and persists for some time after the sound level is lowered again.
This regulating mechanism enables sounds, which increase in volume slowly, to be 'adjusted down', however, it is too slow for sudden sounds, which are therefore perceived 'undampened' and subjectively louder. One of the ear's functions is orientation in space, i.e. to localise sources of sounds. In order to achieve this, the direction and the distance of a sound source have to be determined. Natural sounds are significantly different to technical or synthetic sounds. This explains why we attribute positive associations to natural sounds, whereas technical or synthetic sounds of the same sound level are perceived as noise. We can also hear via the bones in our body. Bones conduct sound very well. When we speak, we hear ourselves with our ears (air conduction) as well as through vibrations of our bones (bone conduction). This is why our own voice sounds unfamiliar to us when it is recorded.