The ability to perceive music (and
sound in general for that matter) is perhaps one of the most influential yet
underrated cognitive functions to have come into existence through evolution. It is utilized by a wide variety of animals, from the simple rhythmic chirp of
a grasshopper to the elaborate melody of a humpback whale song, and is almost
always employed as a means of communicating information, be that location,
identification, an emotional state, or an interest in mating. Most (if not all) humans have
experienced the effects music can have on our emotional state and
research has shown it can also have an effect on physical performance of certain
tasks (e.g.
sports). However, as we all know, not all individuals possess the gift that is
musical talent. The International Laboratory for Brain, Music, and Sound
Research (BRAMS) has devised an online test to measure an individual’s ability
to perceive music and is accessible to the general public via the following
URL: http://www.brams.umontreal.ca/amusia-general/.
But why are some individuals more
talented than others? According to the one estimation, 4-5% of the general
public is considered to have congenital amusia, i.e. they’re born tone deaf.
As is the case in most early research on cognitive functions, scientists have been
able to study the neural pathways involved in musical perception by looking
more closely at individuals with amusia, either congenital or acquired. Researchers
studying musical perception have found congenital amusia to be hereditary and
have outlined some of the neural pathways involved in amusia as shown in
the figure below.
Figure 1. Levels of causation
for the perceptual form of congenital amusia. The musical deficits observed at
the behavioral level (bottom) can be related to a difficulty interpreting
melodic pitches in terms of musical tonal rules. This impairment at the
cognitive level (tonal encoding of pitch) may arise partly from a subtle
problem in acoustical encoding of pitch. The musical-pitch disorder probably
results from an anomalous connectivity between the auditory associative cortex
(BA 22) and the inferior frontal gyrus (BA 47). The brain anomalies should be
ultimately traced back to genes (etiology, top row) since congenital amusia is
hereditary. Genetic predispositions will be modulated by environmental factors
(e.g., musical rehabilitation during childhood). The dashed line emphasizes
that behavior can affect the environment (e.g., avoidance of musical
activities).
From Peretz (2008).
©2008 by Association for Psychological Science.
These
neural pathways are essential for normal musical perception and individuals
with genetic defects or damage to these pathways often demonstrate diminished
ability to accurately process music. However, it isn’t just differences in our
brains that result in the range of musical ability we observe in our day-to-day
experiences. According to more recent research on the auditory system, prenatal
hormone exposure may effect development of the cochlea,
the part of our inner ear responsible for the transduction of sound waves into nervous signals.
The researchers measured the otoacoustic emissions (OAEs; a measure used to evaluate hearing ability)
from the cochleas of heterosexual males and females and found heterosexual
females to have stronger OAEs than heterosexual males. When nonheterosexual
males and females were added in, they found no significant difference between
the male groups while nonheterosexual females showed OAEs comparable to that of
the males.
The results
of this study suggest that there are likely separate and independent causes of
nonheterosexuality in males and females as we would expect nonheterosexual
males to have OAEs comparable to heterosexual females if this wasn’t the case.
More importantly (to the topic of this blog post), prenatal hormone exposure
affects the development of the cochlea such that heterosexual females show
stronger OAEs than the other test groups… but why? This, of course, is a very
difficult question to answer with any certainty, but the results of that study
align with a theory on musical development.
It’s no
secret that caregivers often sing to their infants to calm them down; lullabies were
created for this exact purpose. According to some researchers, this may have
been a critical role for music in our development as a species.
Human babies are born developmentally premature compared to most other animals.
This is because our brain to body size ratio is larger than any other mammals so our brains are not fully developed before we become too big for the womb.
Because our brains are underdeveloped, human infants lack emotional stability.
However, humans are born with the ability to process music and because of this,
caregivers can use music as a tool to influence the emotional state of an
infant.
As all
humans were once infants, it makes sense that we all have the ability to
process music at birth and pass this trait down. However, as heterosexual
females (historically) were most likely to be the caregiver, an enhanced ability to hear and perceive music would be a favorable trait for them to retain into adulthood. This is not
the case with males of either sexual orientation or nonheterosexual females
which would explain why these groups developed to be more similar in terms of
OAE magnitude. I would be interested to see this subject explored much more in
the future as there are many holes in our understanding of the cognitive processes underlying musical perception.
