Re: The Illusion of Music
- From: REVANTH <revanth1993r@xxxxxxxxx>
- Date: Fri, 15 Aug 2008 09:21:47 -0700 (PDT)
This is a fascinating read, particularly this part:
[Perhaps the ultimate illusion in music, however, is the illusion of
structure and form. There is nothing in a sequence of notes
themselves
that creates the rich emotional associations we have with music,
nothing about a scale, a chord or a chord sequence that intrinsically
causes us to expect a resolution. Our ability to make sense of music
depends
on experience and on neural structures that learn and can modify
themselves
with each new song or piece of music we hear, and with each new listen
to music we are
already familiar with. Our brains learn a kind of musical grammar
that
is specific to the music of our culture, just as we learn to speak
the
language of our culture. This becomes the basis for our understanding
of music, and ultimately the basis for what we like in music, what
music moves us, and how it moves us.]
It explains (to my satisfaction, anyway) why I can't stand country/
western/hillbilly/Indian/middle-eastern, etc musics. Although the last
two are much more palatable if accompanied by lissome lasses
demonstrating the finer points of tsiftetelli.
Revanth
On Aug 14, 12:41 pm, Clarity <articlephys...@xxxxxxxxxxxx> wrote:
Music special: The illusion of music
23 February 2008
New Scientist Print Edition
Daniel Levitin
Music in mind
Hear five of the most striking auditory illusions
IMAGINE that you stretch a pillowcase tightly across the opening of a
bucket, and different people throw ping-pong balls at it from
different distances. They can each throw as many balls as they like,
and as often as they like. Your job is to figure out, just by looking
at how the pillowcase moves up and down, how many people there are,
who they are and whether they are walking towards you, away from you
or standing still. This is essentially the problem your auditory
system has to contend with when it uses the eardrum as the gateway to
hearing.
Sound is transmitted through the air by molecules vibrating at certain
frequencies. These bombard the eardrum, causing it to wiggle in and
out depending on how hard they hit it (related to the volume, or
amplitude, of the sound) and how fast they are vibrating (related to
what we call pitch). But there is nothing in the molecules that tells
the eardrum where they came from, or which ones are associated with
which object. Voices may be mixed in with other voices, or the sounds
of machines, wind and footsteps. Most of the time the input is
incomplete or ambiguous. So how does the brain figure out, from this
disorganised mixture of molecules beating against a membrane, what is
out there in the world?
Most people assume that the world is just as they perceive it to be.
Yet experiments have forced researchers, including myself, to confront
the reality that this is not the case. What we actually hear is the
end of a long chain of mental events that give rise to an impression -
a mental image - of the physical world. Nowhere is this more striking
than in the perceptual illusion in which our brain imposes structure
and order on a sequence of sounds to create what we call music.
The chain of mental events begins with a process called feature
extraction. The brain extracts basic, low-level features from the
music, using specialised neural networks that decompose the signal
into information about pitch, timbre, spatial location, loudness,
reverberant environment, tone durations and the onset times for
different notes (and for different components of tones). This bottom-
up processing of basic elements occurs in the peripheral and
phylogenetically older parts of our brains. Next comes a process
called integration. Parts of the higher brain - mostly in the frontal
cortex - receive the basic features from lower brain regions and work
top-down to integrate them into a perceptual whole.
The brain faces three difficulties in feature extraction and
integration. First, the information arriving at the sensory receptors
is undifferentiated in terms of location, source and identity. Second,
the information is ambiguous: different sounds can give rise to
similar or identical patterns of activation on the eardrum. Third, the
information is seldom complete. Parts of the sound may be masked by
other sounds, or lost. The brain has to make a calculated guess about
what is really out there. So, auditory perception is a process of
inference. And when the sensory input is music, these inferences
include several factors over and above the sounds themselves: what has
come before in the piece of music we are hearing; what we remember
will come next if the music is familiar; what we expect will come next
if the genre or style is familiar; and any additional information we
may have, such as a summary of the music that we have read, a sudden
movement by a performer or a nudge by the person sitting next to us.
The brain thus constructs a representation of reality, based on both
the component features of what we actually hear and our expectations
of what we think we should be hearing. There are good evolutionary
reasons for this - a perceptual system that can restore missing
information can help us make quick decisions in threatening situations
- but it is not without drawbacks. The top-down expectations can cause
us to misperceive things by resetting some of the circuitry in the
bottom-up processors. This is partly the neural basis for perceptual
illusions such as the one demonstrated by cognitive psychologist
Richard Warren from the University of Wisconsin. He recorded a
sentence, "The bill was passed by both houses of the legislature", cut
out part of it from the recording tape and then replaced the missing
piece with a burst of white noise (static) of the same duration.
Nearly everyone who heard the altered recording reported that they
heard both a sentence and static. Yet a large proportion of people
couldn't tell when the static occurred because the auditory system had
filled in the missing speech information, so that the sentence seemed
to be uninterrupted.
This filling-in phenomenon is not just a laboratory curiosity.
Composers exploit the same principle, knowing that our perception of a
melodic line will continue, even if part of it is obscured by other
instruments. It also happens whenever we hear the lowest notes on the
piano or double bass. We are not actually hearing 27.5 or 35 hertz,
because those instruments are typically incapable of producing much
energy at these ultra-low frequencies. Instead, our ears are filling
in the information and giving us the illusion that the pitch is that
low.
Most contemporary recordings contain another type of auditory
illusion. Our brains use cues about the spectrum of the sound and the
types of echoes to tell us about the auditory world around us, much as
a mouse uses its whiskers to learn about the physical world around it.
Recording engineers have learned to mimic those cues to imbue
recordings with a real-world, lifelike quality even when they are made
in sterile recording studios. Artificial reverberation makes vocalists
and lead guitars sound as if they are coming from the back of a
concert hall, even when we are listening on headphones and the sound
is an inch away from our ears. The same principles can also generate
auditory tricks, such as making a guitar sound as if it is 10 feet
wide and your ears are right where the soundhole should be.
Special effects
Recorded music allows us to experience other sensory impressions that
we never actually have in the real world. Recording engineers and
musicians create special effects that tickle our brains by stimulating
neural circuits that evolved to discern important features of our
auditory environment. For example, our brains can estimate the size of
an enclosed space on the basis of the reverberation and echo present
in the signal that hits our ears. Even though few of us understand the
equations necessary to describe how one room differs from another, we
can all tell whether we are standing in a small tiled bathroom, a
medium-sized concert hall or a large church with high ceilings. And we
can tell what size room the singer or speaker is in when we hear
recordings of voices. Recording engineers exploit this ability to
create what I call "hyper-realities", playing with our perceptions of
space in the auditory equivalent of the cinematographer's trick of
mounting a camera on the bumper of a speeding car.
Another illusion involves timing. Our brains are exquisitely sensitive
to timing information. We are able to localise objects in the world
based on differences of only a few milliseconds between the time of
arrival of a sound at one of our ears versus the other. Many of the
special effects we love to hear in recorded music are based on this
sensitivity. The sounds of jazz guitarist Pat Metheny or that of David
Gilmour of Pink Floyd use multiple delays of the signal to give an
otherworldly, haunting effect that triggers parts of our brains in
ways that humans had never experienced before, simulating the sound of
an enclosed cave with multiple echoes such as would never actually
occur in the real world - the auditory equivalent of the barbershop
mirrors that repeat infinitely.
Perhaps the ultimate illusion in music, however, is the illusion of
structure and form. There is nothing in a sequence of notes themselves
that creates the rich emotional associations we have with music,
nothing about a scale, a chord or a chord sequence that intrinsically
causes us to expect a resolution.
Our ability to make sense of music depends on experience and on neural
structures that learn and can modify themselves with each new song or
piece of music we hear, and with each new listen to music we are
already familiar with. Our brains learn a kind of musical grammar that
is specific to the music of our culture, just as we learn to speak the
language of our culture. This becomes the basis for our understanding
of music, and ultimately the basis for what we like in music, what
music moves us, and how it moves us.
The Human Brain - With one hundred billion nerve cells, the complexity
is mind-boggling.
Top five musical illusions
In piano works such as Chopin's Fantasy-Impromptu in C-sharp Minor,
opus 66, or Sinding's The Rustle of Spring, the notes go by so quickly
that an illusory melody emerges. When the notes are close enough
together in time, the melody "pops out" because the perceptual system
binds them together, giving an emergent impression of tunefulness.
Play the tune slowly and this disappears.
In a Sardinian style of a cappella singing studied by Bernard Lortat-
Jacob at the Musée de l'Homme in Paris, a fifth female voice called
the quintina (literally "fifth one" in Sardinian) emerges from four
male voices when their harmony and timbres are just right. The voice
is said to be that of the Virgin Mary coming to reward the singers for
their piety, but in fact it is simply a misperception of the chord and
its harmonics.
The Eagles' song, One of These Nights, opens with a pattern played by
bass and guitar that sounds like one instrument. The bass plays a
single note, and the guitar adds a glissando, but the perceptual
effect is of the bass sliding due to the gestalt principle of good
continuation, which binds together two objects when the trajectory of
one implies the continued trajectory of another.
Jazz pianist George Shearing created a new timbral effect by having a
guitar (or in some cases, vibraphone) precisely match what he was
playing on the piano. Listeners come away wondering, "What is that new
instrument?", when in reality it is two separate instruments whose
sounds have perceptually fused.
In Lady Madonna, the Beatles sing into their cupped hands during an
instrumental break and we could swear that there are saxophones
playing. This perception is based on the unusual timbre they achieve,
coupled with our expectation that saxophones should be playing in a
song of this genre. (This is not to be confused with the actual
saxophone solo that occurs in the song.)
They just don't get it
History is littered with figures noted for their hopeless
unmusicality. Ulysses S. Grant, the 18th president of the United
States, had a tin ear and found music profoundly irritating; Che
Guevara famously couldn't distinguish one piece of music from another.
Once, such people would have been described as "tone deaf"; today they
are seen as much more interesting than that.
In the past few years it has become clear that the inability to hold a
tune can sometimes be caused by a neurological condition called
congenital amusia, which completely robs people of what is normally an
instinctive and spontaneous appreciation of music. No wonder the
condition has become a major research topic in the bid to understand
the mysteries of how the brain handles music.
The first case report of "note deafness" appeared in 1878, and the
literature is full of anecdotal accounts of people with a lifelong
failure of music perception. It wasn't until 2002, however, that the
first proper study of congenital amusia was published. A team led by
Isabelle Peretz of the University of Montreal in Canada reported the
case of Monica, a woman in her early 40s who had always lacked even
the most basic of musical abilities (Neuron, vol 33, p 185).
Peretz concluded that Monica's problem was a failure to detect pitch
changes in melodies. Played two notes in sequence, she could rarely
tell whether the second was higher or lower than the first or had the
same pitch. Most people can easily distinguish small differences in
pitch - half a semitone, say - but for amusics, even a leap of an
octave, equivalent to the first two notes of Somewhere Over The
Rainbow, can be barely perceptible. Tones and semitones are the
building blocks of melody, so no wonder amusics find music monotonous
in more than one sense of the word.
Peretz and others have since documented dozens of similar cases. These
people all have normal hearing, intelligence and memory, but
absolutely no grasp of melody. For them, one tune sounds very much
like another, familiar songs are unrecognisable without lyrics, and
dissonant chords that cause most of us to wince elicit no response.
Amusics cannot sing, though they often don't recognise this. The
condition is unusual but not particularly rare - the accepted figure
is 4 per cent of the population - and it runs in families.
So what causes congenital amusia? According to Peretz, the best
explanation is that the human brain is equipped with a specialised
"module" for processing melody, which occasionally fails to develop
properly. That would explain why amusia appears to affect musical
perception alone. If correct, music, like language, is an innate human
adaptation that was hard-wired into our brains by evolution.
AUDITORY CHEESECAKE?
Not everyone agrees with this view, however. Steven Pinker once
famously described music as "auditory cheesecake" - pleasurable but
with no adaptive function. What's more, there is some evidence that
amusia is not a purely musical deficit but is linked to problems with
language or spatial processing. So perhaps amusia (and by extension,
normal music perception) is rooted in the brain circuits that handle
intonation in language, or that look after the concepts of "highness"
and "lowness" central to our mental representations of melody.
Peretz's group and others are now scanning the brains of amusics in
search of anatomical anomalies that might lead them to the underlying
problem. So far they have found some minor differences in the
thickness of white matter in a brain area called the right inferior
frontal gyrus - a region linked with musical pitch perception and
melodic memory (Brain, vol 129, p 2562). They are also searching for
the genes that make amusia heritable, in the hope of gaining new
insight into abnormal brain development in amusia (The American
Journal of Human Genetics, vol 81, p 582).
Another key question is whether congenital amusia is one condition or
several. Some amusics like listening to music because they enjoy the
rhythms, but Peretz's team has found that around half their subjects
have a problem with rhythm perception. This suggests there may be a
related condition that wipes out timing as well as melody. There's
also the problem of "clatterers" - amusics to whom music sounds like a
drainpipe being hit with a wrench. "Only a very few amusics hear
clattering," says Peretz. "For the majority, music is just confusing."
That has led some researchers to propose a separate disorder of music
perception called dystimbria, which prevents people from perceiving
musical "colour", or timbre.
Whether amusia is one condition or many, the hope is that
understanding it better will benefit those unfortunates excluded from
the profound pleasure of music. Peretz thinks that with early
intervention it might be possible to tap into the natural plasticity
of the brain and stem some of the damage. "There's no chance of
helping adults," she says. "We've tried. But with children, maybe."
.
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