13.8 Amusia
Amusia is the name given to a broad class of mental deficits, involving music
perception, that usually appear after brain damage. The deficits include a sharp
decrement in an individual’s ability to grasp musical relationships in the per-
ception of sounds, or in the ability to perform, read, or write music. Most amus-
iacs are capable of understanding spoken language, presumably because their
neurological impairment spared the speech centers of the brain. However, in
many cases amusia accompanies various auditory and speech disorders, such
as the aphasias (the name given to various impairments in the production or
perception of speech).
The degree to which music and speech rely on common neural mechanisms
is not clear. A wealth of cases have shown clear dissociations between impair-
ments in music and in speech, although there may also be individual dif-
ferences in the way that music is handled by brains. Indeed, in many cases,
amusia and aphasia co-occur. There are some separate brain structures, and
some shared structures for processing music and speech. For example, Tallal,
Miller, and Fitch (1993) found that some children who have trouble learning to
speak are unable to process the correct temporal order of sounds. Presumably,
if this is a low-level deficit (i.e., a deficit in a brain system shared by music and
speech systems), it would also affect the ability to process the order of tones in
amelody.
Our current knowledge of the brain’s functional architecture is growing
rapidly, in part due to advances in neuroimaging techniques. PET (positron-
emission tomography), fMRI (functional magnetic resonance imaging), and
ERP (event-related potentials) are three such techniques that are allowing neu-
roscientists to better localize specific brain functions (Posner and Levitin 1997).
For example, neuroscientists have demonstrated that there are specific brain
anatomies for reading (Posner and Raichle 1994), listening to music (Sergent
1993), mentally practicing one’s tennis serve (Roland 1994), calculating num-
bers (Dehaene 1998), and imagining a friend’s face (Kosslyn 1994). Lesions to
certain parts of the brain render patients unable to recognize faces (known as
prosopagnosia—Bruce 1988; Young and Ellis 1989), although their perception of
other objects seems unimpaired. Other lesions cause an inability to read whole
words (a type of alexia), although individual letters can still be made out.
Because music performance and perception involve a number of disparate
and specialized skills, amusia includes a wide range of deficits. One patient
developed an inability to read music note-by-note, but had an intact ability to
read whole musical passages. In another case, a musician lost the ability to play
the piano (his second instrument) although his ability to play the violin (his
first instrument) remained intact. A pianist suffering from aphasia and alexia
was unable to read written music or recognize previously familiar melodies;
however, her music production abilities were spared, so that she could sing the
melody and lyrics to many songs. Following brain damage, an aphasic com-
poser could no longer understand speech but continued to compose without
impairment (Luria 1970).
A knowledge of some of the details of brain architecture makes clearer how
some of these dissociations can occur. For example, reading music depends a
302 Daniel J. Levitin