Download 2 nail illusion Fletcher-Munson Curves Characterizing simple and

Answer:
•If you extend the lines of sight (shown with
darker lines), you'll notice that this creates 2
new intersections (see red dots).
• These intersections are 'false matches', and
represent the correspondence-problem solution
that your visual system arrived at.
• In other words, there are 2 possible sets of
matches, shown by the blue and red dots. While
either is possible, the red (and incorrect) match
was picked. (You can think about why that
match might be preferred.)
2 nail illusion
• You view a pair of nails, one in front of the
other in depth. However, you perceive 2
nails, side-by-side, at the same depth.
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Fletcher-Munson Curves
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Characterizing simple and
complex sounds
The information that reaches the ear does not
• The frequency composition of a sound is called its
spectrum.
• When sounds originate from multiple sources, the
individual waveforms combine so that a single
complex waveform reaches the ear.
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separate sounds from different sources.
• A pure tone contains only one frequency (sine
wave).
• Frequencies in a sound that are integer multiples
of some fundamental frequency are called
harmonics.
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How do we analyze complex
waveforms?
Complex
Sounds
• Simple sounds
– Sine waves are simple harmonic motion; pure
tone
• Complex sounds
– Need Fourier analysis and Fourier synthesis
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Harmonics:
Fourier
Analysis and Synthesis
Fourier components of a complex tone are multiples
of the fundamental frequency
• Fourier transformation
• Two pure tones whose frequencies are
multiples of each other blend into one in our
perception, producing a single tone at the
fundamental (the lower) frequency
– Allows a complex sound wave to be
decomposed into constituent sinusoidal
frequencies, each an integer multiple of the
original’s (fundamental) frequency
– Fundamental frequency (or first harmonic)
determines the pitch of a complex sound
(e.g., a 400 Hz tone and a 500 Hz tone would have
a fundamental of 100 Hz)
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Harmonics:
Components
of Complex
Sound
Harmonics (contd.)
• Musical instruments hardly ever produce
pure tones.
– Instead, when you pluck a string on a guitar, it
will produce a vibration at some fundamental
frequency as well as several multiples (called
harmonics).
• Our perception of timbre is related to the
harmonic composition of a tone.
• This is also the basis of a capella singing.
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Musical Sounds
Sound as a psychological
experience
• Hearing
– Loudness is related to amplitude: sounds get
louder with an increase in amplitude
– Pitch is related to frequency: pitches get higher
with an increase in frequency
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• In addition to an increase of pitch with increase in
frequency, tones are organized into octave.
• Each octave contains seven notes (A, B, C, D, E,
F, and G).
• Two ‘A’ notes in different octaves sound similar
(this similar-sounding quality is called tone
chroma).
• An ‘A’ note one octave above another note has a
fundamental frequency twice that of the lower
note (e.g., A4 = 220 Hz, A5 = 440 Hz, A6 = 880
Hz, etc.)
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Shepard Scale
• One of the most widely used auditory illusions is
Shepard's (1964) demonstration of pitch
circularity, which has come to be known as the
"Shepard Scale" demonstration.
• The demonstration uses a cyclic set of discrete
complex tones, each composed of 10 partials
separated by octave intervals.
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Shepard Scale
Risset Scale
• The tones are co-sinusoidally filtered to produce
the sound level distribution shown below, and the
frequencies of the partials are shifted upward in
steps corresponding to a musical semitone
(= ~ 6 %).
• Another scale that illustrates circularity in
pitch judgment is a continuous scale of JeanClaude Risset.
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The Human Ear
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Overview of the parts of the ear
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The ear is a receiver and transducer of
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The ear and auditory transduction
pressure changes.
• The outer ear:
Directional collector
and amplifier.
• The middle ear:
Impedance matching
and protection.
• The inner ear: Spectral
(frequency) analysis and
transduction.
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Outer Ear
The middle ear
• Pinna:
– The outer fleshy part of the ear helps focus sound
waves
• The middle ear cavity is
filled with air.
• Auditory canal (that part of the ear you're not
supposed to put q-tips in):
• The Eustachian tube links
the middle ear with the
nasopharyngeal cavity so
that the middle ear can
adjust to changes in
atmospheric pressure.
– Has wax to protect from insects and hairs to keep a
constant temperature. also serves to amplify sounds
around its resonant frequency (2,000-5,000 Hz).
• Tympanic membrane (eardrum):
– A taut membrane at the end of the auditory canal that
vibrates with the changes in air pressure at the ear
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• Ossicles:
– Three bones (the smallest bones in the body) that
connect the tympanic membrane of the outer ear and
the oval window of the inner ear.
– The three bones in order are malleus, incus, and stapes.
• The ossicles serve to amplify vibrations (about
22x) between the outer ear and inner ear. This is
necessary since vibrations in the inner ear travel
through fluid which is much more dense than air.
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• Concentrate vibrations of the large
tympanic membrane onto the small
footplate of the stapes (an amplification of
about 17 times).
• Act as a fulcrum and so (because of the way
they are hinged) benefit from the lever
principle (another amplification of 1.3
times)
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The outer and middle ear are
purely mechanical.
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Inner Ear
Transduction and analysis
• Cochlea: a coiled liquid-filled structure.
begin at the inner ear.
– The liquid inside the cochlea vibrates because the
stapes pushes on the oval window (at the base of the
cochlea).
– The cochlea has three layers:
• The cochlea is the site at
which vibrations of the
stapes and inner ear fluid
are transduced to neural
responses in fibers of the
auditory nerve.
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The ossicles amplify in two
ways:
Middle Ear
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• scala vestibuli,
• scala tympany,
• and the cochlear partition.
• Inside the cochlear partition is the organ of corti,
which is the site of auditory transduction.
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The inner ear
The cochlea is a coiled tube that resembles a
snail shell
• Part of the inner ear is concerned with balance (vestibular
system).
• The part of the inner ear that contains the receptor cells for
hearing is the cochlea.
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• In humans, the
cochlea coils
about 2.5 times.
• A cross-section
through the coiled
cochlear tube
reveals that the
inside is divided
into three
compartments.
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The organ of Corti
• The receptor cells are located in the scala media, on the
organ of Corti.
• Composition of the fluids in the three compartments is
different.
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The organ of corti
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•
•
•
Contains inner hair cells and outer hair cells.
Sits on top of the basilar membrane.
Is covered by the tectorial membrane.
Auditory transduction:
– When the basilar membrane moves up and down, the
cilia of the outer hair cells (small hair-like projection
off of the hair cells) rub against the tectorial membrane.
– The bending of the cilia produces and electrical
response in the hair cells.
• Inner hair cells help amplify vibrations of the
basilar membrane.
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