file0_1490

What Is Music? 27tone as the basis for their music, and most people can’t reliably detectchanges smaller than about one tenth of a semitone.The ability to detect differences in pitch is based on physiology, andvaries from one animal to another. The basilar membrane of the humaninner ear contains hair cells that are frequency selective, firing only inresponse to a certain band of frequencies. These are stretched outacross the membrane from low frequencies to high; low-frequencysounds excite hair cells on one end of the basilar membrane, mediumfrequency sounds excite the hair cells in the middle, and high-frequencysounds excite them at the other end. We can think of the membrane ascontaining a map of different pitches very much like a piano keyboardsuperimposed on it. Because the different tones are spread out acrossthe surface topography of the membrane, this is called a tonotopic map.After sounds enter the ear, they pass by the basilar membrane, wherecertain hair cells fire, depending on the frequency of the sounds. Themembrane acts like a motion-detector lamp you might have in your garden;activity in a certain part of the membrane causes it to send an electricalsignal on up to the auditory cortex. The auditory cortex also has atonotopic map, with low to high tones stretched out across the corticalsurface. In this sense, the brain contains a “map” of different pitches, anddifferent areas of the brain respond to different pitches. Pitch is so importantthat the brain represents it directly; unlike almost any other musicalattribute, we could place electrodes in the brain and be able todetermine what pitches were being played to a person just by looking atthe brain activity. And although music is based on pitch relations ratherthan absolute pitch values, it is, paradoxically, these absolute pitch valuesthat the brain is paying attention to throughout its different stages ofprocessing.A scale is just a subset of the theoretically infinite number of pitches, andevery culture selects these based on historical tradition or somewhat arbitrarily.The specific pitches chosen are then anointed as being part ofthat musical system. These are the letters that you see in the figureabove. The names “A,” “B,” “C,” and so on are arbitrary labels that we as-