Although we consider sound to be a single stimulus, it can actually be divided into two distinct parts: a physical or vibrational sound wave as well as a psychological aspect or tone. For example, when we hear a tone, we may first recognize the highness or lowness of the sound, or its pitch. The recognition of pitch, however, is dependent upon the frequency of the tone. When a tone has a high frequency, it has a large number of sound waves passing though a particular period and we will perceive a high pitch.

Each of us has a particular sensitivity to changes in frequency which allows some people, such as musicians, to hear very slight changes in pitch, while others have difficulties distinguishing between tones. This variable is called the difference lumen (DL). In the early 20th Century, some researchers were very interested in the variation of pitch determination between individuals. In 1919, C.E. Seashore published his findings which indicated that pitch determination was an innate characteristic. After further experimentation, he found more evidence to support this claim and in 1938 wrote, "Pitch sensitiveness in the ear reaches its maximum very early [in life]...the physiological limit for hearing pitch does not improve with training" (Lundin, 23). That same year, however, similar experiments were done using slightly different teaching methods. After a dozen fifty-minute sessions, Ruth Wyatt's research showed that in musicians and non-musicians alike, there was a definite long-term improvement in pitch discrimination. These findings gave the first solid indication that these was a great deal of neural plasticity in the auditory cortex.

The receptive field within the auditory cortex consists of neurons which have heightened sensitivity to a single pitch (what some researchers have called the "best pitch"). Resent research has indicated, however, that there is a great deal of plasticity within the primary auditory cortex when pitch is used as a controlled stimulus in associative learning.

Although pitch as a function was observable for many centuries, pitch was not applied as a specific formula for music until 600 A.D. when Pope Gregory the Great and his monks created a system for music. After noticing that similar sounds were being created-some higher and some lower- he told all his monks, who each were required to play the organ, to use a single name for each distinct note. They found only seven separate notes, and named them a, b, c, d, e, f, and g. As these notes were repeated, both higher and lower, octaves of notes were formed. Later, some of these notes were subdivided so that, in the end, there were 12 different pitches of equal ratios within each octave (what we now refer to as a chromatic scale). This was by no means the beginning of music, but it did provide a formula to record music that could be used by all people. (Meyer, 66-68)

Although music can be broken down into a series of pitches, music perception produces activity in a much larger area than where specific pitches are perceived. Listening to music produces activation throughout the bilateral fronto-temporal and parieto-temporal brain areas (Gruhn, 1997). However, the way in which music is learned involves stimulation of different areas of the brain.

I have summarized two experiments which talk specifically about music perception. The first experiment addresses how pitch can be used as a conditioned stimulus, resulting in receptive field plasticity in the auditory field. The second experiment deals directly with how music is learned and which corical areas are stimulates. For more information, you can go back to the Music Perception area found within our Music and Auditon homepage.