In all sensory systems an important part of the neural code is determined by what location of the sensory organ is stimulated. In the case of the eye, a spot of light falls on a few photoreceptors and they excite nerves that map onto a representation of the visual world in the brain. In the ear, the acoustic world is coded by a one-dimensional representation of frequency. This frequency map then projects to the brain which performs the almost unbelievable task of reconstructing the original three-dimensional acoustic world. There are actually parts of the brain that contain a true three-dimensional representation of the outer world so that the sound of a twig snapping behind you excites nerve cells in one location while a twig snapping on your right excites nerve cells in another spatially precise location. The analysis of speech appears to take place in parts of the brain that are highly developed only in man. The amazing machinery that accomplishes the reconstruction of the acoustic world relies on the delicate structures of the inner ear that deconstruct the original sounds. The rest of this journal describes current efforts to fully understand how the ear works and the health problems that it may encounter.
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