Universal and Non-universal Features of Musical Pitch Perception Revealed by Singing
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Universal and Non-universal Features of Musical Pitch Perception Revealed by Singing


[MUSIC PLAYING] [PLAYING FLUTE] JOSH MCDERMOTT: Perception
and cognition result from some sort of complex
interplay between our genes and our experience. But in humans, the vast
majority of experiments that have been conducted are
on members of Western societies because that’s where most
of the scientists are. The experiences of
those kinds of people are relatively homogeneous. We don’t know a whole lot about
how much variation is possible that might be driven by
experiential variation. NORI JACOBY: Now one
domain in which this is extremely prominent is music. Music is present in
all known cultures. And this suggests some
kind of a biological basis. However, music is also very
different from one place to another. JOSH MCDERMOTT: Now one of
the key ingredients of music is pitch. And pitch perception has been
extremely well documented in Western listeners. And there’s a bunch
of salient properties that we now know about. So one of those
properties is the fact that pitch seems to have
an upper and a lower limit. NORI JACOBY: Now even though
we can hear frequencies that are as high as 20 kilohertz
if our hearing is very good, musical pitch perception
tends to break down at about 4 kilohertz,
which is around the highest tone of the piano. Now if we play melody within
the range of the piano, something like that– [PLAYS “TWINKLE, TWINKLE LITTLE
STAR”] –it’s easy to recognize it. But if using a
synthesizer, I will play you a melody outside the
range of the piano, higher than 4 kilohertz. Then it will be harder
to recognize the melody and the sense of pitch
will be less salient. [PLAYS “TWINKLE, TWINKLE LITTLE
STAR”] So there’s something different
about the pitch information we can extract from
low frequencies– [PLAYS PIANO] –compared with
high frequencies. [PLAYS PIANO] JOSH MCDERMOTT:
Now one explanation for that is that there
is a phenomenon that happens in the ear
known as phase locking. So the action
potentials, the spikes that are fired in
response to sound, are temporally very precise. But there’s a
biophysical limitation to the ion channels
in the ear that causes phase locking to break
down when the frequencies get sufficiently high,
typically above about 4 kilohertz in the animal
species in which this has been measured. So one classical explanation
for the upper limit of pitch is that there is a biological
limit on the information that’s coming out of the ear. NORI JACOBY: Now on the
other hand, in Western music, there is also a limit to the
pitches that are being used. For example, in
the Western piano, the highest tone is
about 4 kilohertz. [PLAYS TONE] JOSH MCDERMOTT:
Now, of course, it could be that Western
instruments are adapted to the limits
of pitch perception. But the other possibility
is that our pitch perception is actually adapted to what
we hear in Western music. And pitch perception is not as
good at very high frequencies because we just don’t
ever have to extract pitch information from
frequencies that are that high. So if you just test
Western participants, it’s always going
to be ambiguous. Now another very
salient property of pitch in Western
music is that notes that are separated by octaves
are treated as equivalent. NORI JACOBY: A basic feature
of Western music is so-called octave equivalence, where
tones separate by an octave– [PLAYS TONES] –are the same. This is familiar to us from
using the same notes’ name, for example here, C– [PLAYS Cs] –for tones at
different registers. [PLAYS Cs] Here we have a Western piano. And the pattern of
black and white keys are organized in octaves. There’s also tons of
octaves in Western harmony. [PLAYS CHORDS] What’s really fascinating
is that octaves are also tightly linked to acoustics. So for example, if two
strings have the same tension and one is twice as
long as the other, then this tone will
sound an octave below. [PLAYS OCTAVE] JOSH MCDERMOTT: In order
to get some insight into the potential role
of biological constraints and experience
with Western music in these kinds of
phenomena, there’s a society known as the
Tsimane in the Bolivian Amazon rainforest that we’ve been
working with for the past eight years. NORI JACOBY: These villages
were geographically remote and from the local cities. And we had to travel there by
taking a canoe ride or a Cessna plane or a few hours in a truck. And we found
participants that have different exposure compared
with the participant in the modern US city. JOSH MCDERMOTT: They don’t have
electricity or running water. They’ll make occasional trips
into nearby towns to trade, but that’s pretty much the
extent of their contact with the Western world. NORI JACOBY: The
experiment was very simple. We played tones that are
well above the singing range, something like that– [PLAYS HIGH NOTES] –to the participant. And participant
reproduced these tones, singing comfortable in
their singing range. So for these tones– [PLAYS HIGH NOTES] –the sang something
like (SINGING) ha ha. JOSH MCDERMOTT: So when
we do these experiments on Westerners, we find what
you would expect, namely that reproductions are good
when the frequencies are in sort of the classical
range of musical pitch and then deteriorate when
the frequencies get too high. NORI JACOBY: The pitch
range of Tsimane music is more limited compared
with Western music. So they don’t have a piano. And when we’ve gone
to these villages and asked them to show
us their instruments and play them to us, we
realized that the upper limit that we’ve ever seen produced
is usually under 2 kilohertz. JOSH MCDERMOTT: All right. So if we really think that
the limits of pitch perception are determined by the limits
of what you hear in music, then we might
expect, if anything, that the upper limit of pitch
would be lower in the Tsimane. [PLAYS HIGH PITCHES ON COMPUTER] [? AUDIENCE: ?] [SINGS PITCHES] [PLAYS HIGH PITCHES] [? AUDIENCE: ?] [SINGS PITCHES] [PLAYS HIGH PITCHES] AUDIENCE: [SINGS PITCHES] JOSH MCDERMOTT: However,
when we do these experiments and we measure the accuracy
of the reproductions, instead we actually find that
the dependence on frequency is actually remarkably similar. So as you can see in the
graph, their overall accuracy is a little bit lower. But the dependence of
accuracy on frequency is actually quite similar to
what you see in Westerners. So that suggests that there
is some non-musical constraint that’s actually driving
this phenomenon, potentially some biological limit on the
upper limit of phase locking. Now to assess
octave equivalence, we can take the
exact same experiment and analyze it in
a different way. NORI JACOBY: We found that US
participants try to also create the relation, an
octave relation, between the tone that they
heard and the tone that they sang back. JOSH MCDERMOTT:
So as to replicate what we call the chroma, or
the letter name of the note. So if you play them an
A in an upper register, they’ll tend to sing back
in A in their singing range. [PLAYS NOTES] [? AUDIENCE: ?] [SINGS PITCHES] [PLAYS NOTES] [? AUDIENCE: ?] [SINGS PITCHES] JOSH MCDERMOTT:
So this phenomenon is extremely pronounced in
Western musician participants. It’s reduced but
still very salient in Western non-musicians. And the question is, what was
going to happen in the Tsimane. And as you can
see in this graph, chroma matching is
absent in the Tsimane. So even though they accurately
reproduce the direction and to some extent the
interval between the two notes, the absolute
pitches that they produce are not related to the absolute
pitches of the stimulus. NORI JACOBY: This suggests
that octave equivalence is culturally contingent. JOSH MCDERMOTT: So
these experiments have given us new
insights into the origins of different aspects of
musical pitch perception. And to me what’s most exciting
about them is that they reveal dissociations between different
parts of pitch perception that are pretty tightly
linked in Westerners. And so I think
they really suggest that pitch perception is a
lot more interesting than you might expect. There’s a whole bunch of
different facets to it. And those can be teased apart
if you respect the diversity of human experience.

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