The Cognitive Neuroscience of Music

into 12 discrete, equal, logarithmic steps. Each step within the octave is called a semitone,
and the F 0 s of adjacent semitones differ by a factor of 21/12, or about 6 per cent. The chro-
matic scale is made up of all 12 tones in the octave, whereas the major and minor (diatonic)
scales are made up of partially overlapping sets of seven tones in the octave. Harmonic
intervals and melodic intervals are named according to the scale relationship of the upper
note to the lower note. Thus when the fifth note in the major or minor scale sits atop the
first note on the scale, the interval is called a fifth(Figure 9.1D). The note named A 4 is
assigned an F 0 value of 440 Hz. The letter name of each note corresponds to one of the
12 notes in the octave; the number of each note indicates the octave the note is in, with
increments at each occurrence of C along the scale (e.g....A 4 —A# 4 —B 4 —C 5 ...). The

    131

Transverse gyrus

of heschl

Geniculocortical

radiations

Medical geniculate body

Inferior colliculus

Lateral

lemniscus

Superior olivary

complex

Auditory Trapezoid body

nerve

Cochlear nucleus

Cochlea

A

B

C

Figure 9.2The auditory system. (A) Magnetic resonance image (coronal section) through the transverse gyri of
Heschl and the superior temporal gyri of case MHS, who suffered bilateral infarction nine years earlier.White
arrowspoint to the region of the transverse gyrus of Heschl in the right (R) and left hemispheres (L). The results
of psychoacoustic experiments performed by MHS are shown in Figure 9.7. (B) The inner ear and the auditory
nerve, the obligatory pathway from the cochlea to the cochlear nuclei in the lower brain stem. (C) Schematic of
the central auditory pathway showing the main relay stations and projection patterns. Adapted from Tramo et al.^15
(A), Helmholtz^16 (B), and Davis^17 (C).