We are conducting several studies that examine the neural correlates of absolute pitch. In addition, we are exploring the occurrence of absolute pitch in families and in certain neurological conditions (developmental disorders, brain adaptations during development). The following write-up provides a short overview on absolute pitch and our studies.
1. What is absolute pitch?
Absolute Pitch is defined as the ability to identify a particular pitch of
the Western musical scale without any external reference tone and independent
of frequency range or timbre (Ward and Burns, 1980; Miyazaki, 1988, 1989;
Takeuchi and Hulse, 1993). Humans generally hear musical tones in a melodic
context in which they can distinguish repetition, rising or falling pitch
as well as the overall contour of a series of tones forming a melody. Musicians
with absolute pitch are able to categorize the components of these musical
patterns: the musical tones themselves (Siegel, 1974; Burns and Ward, 1978;
Burns and Campbell, 1994; Miyazaki et al.,1988; Rakowski et al., 1993). Unique
among musicians with AP is the ability to reliably assign note names to musical
tones. Miyazaki (1988) found that the boundaries for these pitch classes were
very reliable within each AP musician and very similar across different individuals
with AP. In contrast to absolute pitch, relative pitch is the ability to identify
a tone in relation to another tone, or absolutely if a reference tone is provided.
This ability can be "perfect" (through intense training) which is
the reason that the colloquial term "perfect pitch" is not a good
term to describe absolute pitch ability. It is thought that AP musicians have
an internal representation of tones or pitch height. Consistent with this
hypothesis is the observation that AP possessors might hear sharp when they
become older (Vernon, 1977). A mismatch might develop between the internal
representation of a tone (after seeing this tone on the staff or after being
given the name of the tone) and the auditory percept. The cause for this mismatch
is a loss in the elasticity of the basilar membrane in the inner ear with
aging, which might change it's resonance.
AP is typically defined empirically using such methods as tone height identification,
vocal tone production, or pitch memory experiments with variable intervals
between the target and probe tones, in which the interval can be filled with
various distractors. Typically, there is a good correlation between self report
and test results (Zatorre and Beckett, 1989; Schlaug et al., 1995; Keenan
et al., 2001). We have only seen two out of more than 80 subjects tested that
did not have absolute pitch despite the fact that they reported it.
AP musicians were not found to be better in tone discrimination than non-AP
musicians (Bachem 1954; Burns and Campbell, 1994; Levitin, 1996), or octave
register (Miyazaki, 1988) or musical interval identification (Miyazaki, 1993).
For people with absolute pitch, naming a note is as simple and immediate as
naming a color of an object for others. No particular effort is associated
with this and they do not have to make a conscious comparison with an internal
template, although they can if they want to. Many great musicians had absolute
pitch (e.g., Bach, Mozart, Beethoven) but there are also many famous musicians
and composers who did not have it. Absolute pitch does not seem to have a
relevance to musicianship or musicality, although it is useful for music theory
classes in college and university. AP ability can even be a hindrance in some
circumstances and it is known that AP musicians sometimes try to suppress
their AP ability when they are making music with others (e.g., singing in
a choir).
The anatomical, perceptual and/or cognitive processes that underlie AP ability
are not known. There are several theories with regard to differences in the
perceptual and cognitive strategies comparing AP with non-AP subjects, which
range from categorical perception, to verbal encoding, to the use of internal
pitch templates, or to a better or different long-term memory in AP musicians.
The most influential study to suggest a categorical perception/verbal encoding
in AP was conducted by Siegel (1974). She showed that musicians with AP are
able to use two strategies to remember pitches: (I) they encode every tone
verbally (verbal mode) or (ii) they encode and memorize the frequency of every
tone (sensory mode). Non-AP musicians can only use the sensory mode. When
AP musicians have the advantage of labeling the stimuli with musical names
in a pitch memory task, AP show superior pitch memory performance. If AP musicians
are forced to use their sensory encoding mode, they are not better in a pitch
memory task than non-AP musicians. Therefore, Siegel (1974) concluded that
AP musicians perceive and process pitches categorically which has been supported
by other researchers (Burns and Ward, 1978; Burns and Campbell, 1994; Rakowski,
1993). In a later publication, Siegel (1977) made a comparison between the
categories for pitch in musicians with AP and the categories for phonemes
in speech. Others have suggested that there may not be just one encoding strategy
for AP musicians and that the encoding may also involve visual and kinesthetic
strategies besides a verbal strategy (Zatorre and Beckett, 1989).
An alternative hypothesis is that AP musicians have an internal (reference)
template of tones of the musical scale. The conscious or unconscious comparison
of every auditory stimulus with this internal template enables the AP musicians
to identify every tone. Some support for this theory comes from studies by
Langner (1997) which suggest that brainstem cochlear neurons might show special
oscillations which might provide an internal pitch reference. Further support
comes from auditory memory experiments. Studies have reported a smaller or
absent P300 component (Klein et al., 1984; Waymann et al., 1992) indicating
that the working memory of AP-musicians is - due to the already existing internal
auditory template - not as much involved in a pitch memory task as compared
to musicians without AP. However, a recent study showed no difference in the
P300 component which might indicate that AP musicians do not always access
this internal template (Hirose et al., 2002).
2. Is there a genetic basis for AP?
Early commencement of musical training seems to be a key factor in developing
absolute pitch (Sergeant, 1969; Krumhansl, 1991; Gregersen et al., 1999; Keenan
et al., 2001). In one study it was shown that AP musicians began musical training
at 5.4 +/- 2.8 years compared to non-AP musicians who began training at 7.9
+/- years of age (Gregersen et al., 1999). Other studies have shown that almost
all musicians who developed absolute pitch started before the age of seven
and that it was extremely unlikely that absolute pitch would develop if a
musician started after the age of 10 (Sergeant, 1969) These reports suggest
that a critical period exists during which absolute pitch develops which may
be analogous to the critical period for native language acquisition (Jusczyk
et al., 1993). It may even be that the same critical period for native language
acquisition also exists for perceiving pitch information absolutely. It is
interesting to remember that phonemes are the prototypical examples of categorical
perception. Creating categories for pitch and enabling absolute pitch musicians
to perceive pitches as belonging to distinct categories, may draw upon the
same neural structures that are used for perceiving phonemes.
The prevalence of AP has been estimated to be between 1/1500 to 1/10000 in
the general population (Bachem, 1955; Profita and Bidder, 1988;Takeuchi and
Hulse, 1993;). However, these prevalence estimates in the general population
are hampered by the problem of not being able to test for AP in a general,
non-musician, population. The prevalence of AP among musicians is estimated
to be between 5-50/100 with the highest number reported among Asian musicians
in conservatory type music schools (Revesz, 1913; Wellek, 1963; Chouard and
Sposetti, 1991; Gregersen et al., 1999). Several reports have indicated that
there is a higher prevalence among asians compared to caucasians (Miyazaki,
1988; Gregersen et al., 1999). It is thought that these cultural differences
may be due to a more vigorous early music training program or perhaps the
more prevalent use of a training program that relies more on auditory than
visual cues (e.g., Suzuki method).
In this regard, it is of interest that Deutsch et al. (1999) found some evidence
for "absolute pitch" ability in tonal language speakers (e.g., Vietnamese,
Mandarin). In these tonal languages words can take on a different meaning
if "tones" are enunciated in different ways. Deutsch and colleagues
found an extraordinary consistency of pitch information used in these words
across different testing sessions. Although this study indicates that speakers
of tonal languages may have a very precise form of pitch memory, the absolute
pitch ability of an AP musician is very different. An AP musician is able
to recognize more than 70 pitches without any effort and shows the same consistency
in reproduction as a native tone speaker, but with many more tones. Nevertheless,
these observations could uncover new links between music and language and
it would certainly be of interest to determine whether the higher prevalence
of AP in Asian musicians is due to a more vigorous early music program or
due to a greater sharing of neural substrates between language and music.
Profita et al. (1988) were the first to examine whether or not a genetic trait
could underlie AP ability. Based on his observations, he suggested an autosomal
dominant trait with reduced penetrance. More recently Gregersen et al. (1999)
and Baharloo et al., (1999, 2001) have found evidence for an increased prevalence
of AP in families. However, a family history of music, and having older siblings
that play musical instrument might be confounds and might increase a younger
siblings chance of developing AP. Of interest is also a report by Drayna et
al., (2001) which found a more similar performance in detecting incorrect
notes in popular melodies between monozygotic twins compared to dizygotic
twins. This study did not examine a genetic basis for absolute pitch, although
it suggests that a genetic component for pitch or pitch interval processing
exists.
3. Can AP be learned?
Numerous experiments have been done over the last century to determine whether
AP can be learned (Meyer, 1899; Cuddy, 1968, 1970; Takeuchi and Hulse, 1993).
There is even an industry that has evolved around learning "perfect pitch".
The result of all of these studies is that genuine AP cannot be learned by
adults. At most, it has been shown that individual subjects have been able
to memorize one or a few tones for a while if they practice listening to them
again and again, but this ability diminishes if this practice is stopped.
A good example of this kind of absolute memory for one or a few tones is the
perfect "A" that many string players have.
Some reports suggested that absolute pitch ability may be more prevalent than
was traditionally assumed and that non-musicians may actually possess absolute
pitch ability without knowing it. Halpern (1989) found that musically untrained
subjects were quite consistent when they were asked to hum the first notes
of well-known tunes when tested on different occasions. Levitin (1994) took
this further and compared recordings of popular tunes with subject's own productions
of these tunes. He showed that almost half of the non-AP test subjects came
within 2 semitones of the correct pitch of the most popular recordings. Thus,
some subjects may possess some form of highly accurate pitch memory, however,
there is ample data to suggest that the genuine AP ability that AP musicians
have is not a memory function (Siegel, 1974; Takeuchi and Hulse, 1993).
There is some evidence that infants may have an absolute pitch ability (Saffran
and Griepentrog, 2001). However, whether the memory for musical phrases is
really absolute may need to be explored further. Furthermore, we would need
to understand what aspects and factors in development would make the majority
of a population loose this ability after infancy.
4. Is there an anatomical basis for absolute
pitch?
In examining hypothetical claims of differences in hemispheric dominance between
musicians and non-musicians (Schlaug et al., 1995), we found a significant
difference in the planum temporale asymmetry (a structural marker of hemispheric
dominance) with musicians being more lateralized towards the left (Schlaug
et al., 1995). Post-hoc analyses revealed that this difference was mainly
due to musicians with absolute pitch. This was further refined in a replication
study (Keenan et al., 2001). In addition to replicating our original results,
we were able to determine that the increased leftward PT asymmetry in AP musicians
was seen even after both groups of musicians were matched for early commencement
of musical training. Furthermore, we found that the right PT was significantly
smaller in the AP group compared to the non-AP music group and a matched non-musician
control group. Thus, the smaller right PT was the determining factor for the
increased PT asymmetry found in absolute pitch musicians. In an unrelated
sample, Zatorre et al. (1998) confirmed some of these morphometric results
by finding a greater leftward PT asymmetry when a small group of AP musicians
was compared with a large sample of control subjects. The planum temporale
(PT) is part of the superior temporal gyrus and contains auditory association
cortex. The PT itself could be part of the neural correlate of absolute pitch
or it could be a structural marker for increased temporal lobe asymmetry which
might underlie AP ability. However, recent functional studies indicated that
the PT becomes activated when AP musicians use their AP ability (Schlaug,
2001; Ohnishi et al., 2002).
5. Are there functional brain correlates of the perceptual and cognitive correlates
that underlie absolute pitch?
Zatorre et al. (1998) performed a functional imaging study using positron
emission tomography (PET) and found activation during a tone-listening task
in the left dorso-lateral portion of the frontal cortex in AP but not in non-AP
subjects. This region was also activated in an interval judgment task in musicians,
regardless of their AP ability. It was interpreted that AP musicians used
the dorso-lateral frontal region for developing verbal-auditory associations.
In an MEG study, Hirata et al. (1999) described a functional correlate of
the anatomical PT asymmetry by finding distinct neural activities in the posterior
temporal lobe (within the planum temporale region) when AP subjects listened
to tones. This activity was significantly more posterior than that in non-AP
musicians.
Ohnishi et al. (2001) collected whole-brain fMRI data from fourteen musicians
(ten with AP), and fourteen non-musician control subjects, during alternating
24s blocks of listening to music and background noise. They found that the
musician group showed bilateral but left-lateralized superior temporal, as
well as left dorsolateral frontal changes between music and background noise
blocks. In non-musicians, the changes were similar in the posterior temporal
cortex, although the musicians showed significantly greater changes in the
PT. Interestingly, among the musicians studied, there was a significant correlation
between years of training and the involvement of the left PT, as well as a
correlation between involvement of left PT, dorso-lateral frontal cortex and
AP ability.
Similar findings were obtained by our own experiments (Schlaug, 2001). We
used a functional MRI experiment to contrast two conditions: a phoneme and
a pitch memory task. Subjects performed a "2-back task" and a forced-choice
paradigm was used requiring subjects to indicate whether each new tone or
each new phoneme was the same or different, compared to two tones or two phonemes
before. A motor condition with alternating button presses served as a control
condition. AP musicians, non-AP musicians and nonmusicians showed pronounced
left-sided superior temporal lobe activation in the phonemes vs control tasks
comparison. Similar activations were seen in the tones condition for the AP
musicians. However, the non-AP musicians as well as the nonmusicians showed
either symmetric or right-sided activations of the superior temporal lobe.
6. Summary
There appears to be at least one non-genetic factor for absolute pitch, which
is age of commencement of musical training. Several large studies found that
early age of commencement of musical training is a major determinant for developing
absolute pitch. A genetic component for the expression of AP is being discussed,
although it is unclear whether an AP gene would be coding for the AP behavior,
a specialized brain function, or brain structure. The PT asymmetry, or functional
dominance of the left over the right planum temporale during development may
be an additional factor besides age that could determine the behavioral phenotype
of AP. The higher incidence of AP in Asians and the associations between AP
and tonal languages need to be further explored. Similarly, presumed developmental
changes in AP ability (higher incidence in infants but rare in adults) might
offer new insights into the underlying neural correlates of this ability.
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