Address for correspondence: Dr. Mark Jude Tramo, MGH EDR-405, 55 Fruit Street, Boston, MA 02114-2696. Voice: 617-726-5409; fax: 617-726-5457.
mtramo{at}hms.harvard.edu
Basic principles of the theory of harmony reflect physiological
and anatomical properties of the auditory nervous system and
related cognitive systems. This hypothesis is motivated by observations
from several different disciplines, including ethnomusicology,
developmental psychology, and animal behavior. Over the past
several years, we and our colleagues have been investigating
the vertical dimension of harmony from the perspective of neurobiology
using physiological, psychoacoustic, and neurological methods.
Properties of the auditory system that govern harmony perception
include (1) the capacity of peripheral auditory neurons to encode
temporal regularities in acoustic fine structure and (2) the
differential tuning of many neurons throughout the auditory
system to a narrow range of frequencies in the audible spectrum.
Biologically determined limits on these properties constrain
the range of notes used in music throughout the world and the
way notes are combined to form intervals and chords in popular
Western music. When a harmonic interval is played, neurons throughout
the auditory system that are sensitive to one or more frequencies
(partials) contained in the interval respond by firing action
potentials. For consonant intervals, the fine timing of auditory
nerve fiber responses contains strong representations of harmonically
related pitches implied by the interval (e.g., Rameau's fundamental
bass) in addition to the pitches of notes actually present in
the interval. Moreover, all or most of the partials can be resolved
by finely tuned neurons throughout the auditory system. By contrast,
dissonant intervals evoke auditory nerve fiber activity that
does not contain strong representations of constituent notes
or related bass notes. Furthermore, many partials are too close
together to be resolved. Consequently, they interfere with one
another, cause coarse fluctuations in the firing of peripheral
and central auditory neurons, and give rise to perception of
roughness and dissonance. The effects of auditory cortex lesions
on the perception of consonance, pitch, and roughness, combined
with a critical reappraisal of published psychoacoustic data
on the relationship between consonance and roughness, lead us
to conclude that consonance is first and foremost a function
of the pitch relationships among notes. Harmony in the vertical
dimension is a positive phenomenon, not just a negative phenomenon
that depends on the absence of roughness—a view currently
held by many psychologists, musicologists, and physiologists.
