PSY280 - 8. Sound Flashcards
sound: physical definition
pressure changes in the air
how we detect + translate simple sounds and construct auditory scenes
sound: psychological definition
our experience of the physical dimension
Pressure changes
driven by vibrations that affect surrounding medium vibrations of an object that affects medium - most cases air
speakers: object produces vibrations
produce sound waves, compose of regions of condensation & rarefaction
Pressure changes
pattern of rhythmic pressure changes in air - propagate out from source
as it moves toward you, it compresses air molecules - condensation
as it moves away from you, it pulls molecules apart - rarefaction
alternating low + high pressure
Pressure changes
Sound waves represented mathematically using sine waves: plots rhythmic changes
amplitude: height of wave - highest to lowest
frequency: how many peaks exist in a given point of time
more peaks = higher frequency
sound waves
amplitude= loudness - higher the amplitude, louder sound frequency= pitch - higher frequency,higher the pitch
sound waves: units & limits
amplitude: dB, 0–140dB (pain)
frequency: hertz (Hz), ~20–20 000 Hz but changes as we age
Hz - 1 cycle per second from peak to peak
sound waves: units
dB = 20 log p0
p0 = 0.00002 dyne / cm2
flexible unit - measurement of ratio of sound pressures
p0 is reference: lowest pressure change detectible
p = pressure for sound
0 is a reference point - arbitrary
sound waves: units
immediate hearing loss above 140 dB
first sensation is pain rather than sound
log unit, so not a log scale
small changes in dB can result in large physical changes
sound waves: limits
for range of hearing in humans, relationship between frequency & amplitude is not uniform
some very low frequency sounds need to be at a high intensity (amplitude) to be able to perceive them
sound waves: limits
speech in a protected range in the middle - language important for human condition
before we get to pain, we get high risk threshold
hearing loss starts is high frequency range
speech ends at 12,000 Hz
Elephants
can detect very low frequency vibrations so that they can tell when other large animals are nearby - sensitivity to low rumbling sounds
diff species have diff ranges
higher range for dogs + cats - dog whistle, can’t detect it because it is outside our range
Complex tones
sound waves that consist of more than one sinusoidal component of different frequencies
mostly deal with complex tones
even in same note, but have more than 1 frequency
we can apply mathematical formula to pull apart diff sine waves
Pure tones
represent pressure changes that occur in perfect sine wave pattern
few sounds are ever this simple
Fourier analysis
Sounds can be divided into component sine waves
Components are called harmonics
partial out diff sine waves of diff amplitude + frequency embedded in it
spectrum
summary of the Fourier analysis
plot them on graph with frequency as x axis + amplitude as y axis
fundamental frequency
lowest frequency harmonic
fundamental frequency in figure is 200, each subsequent harmonic is multiple of fundamental frequency
harmonic spectrum
composed of harmonics that are multiples of fundamental frequency
harmonic spectrum
continuous spectrum: represents white noise, contains all of diff frequencies at approximately equal intensity
missing fundamental frequency - fill it in - recognize there’s a missing 200 frequency
but not missing in our perception, just the physical stimulus
Pitch
psychological aspect of sound related mainly to fundamental frequency
most closely related to musical notes
rate on a scale from high to low
can calculate based on harmonics present
2 instruments can produce same pitch but sound different
Timbre
psychological sensation that helps distinguish 2 sounds with similar loudness & pitch
same harmonics, but represented to a diff amplitude
shape of spectrum allows us to distinguish
trombone more of the high frequency harmonics
we refer to it as the warmth in a sound
Timbre
based on differences in harmonics, attack & decay
buildup of sound over time
attack: buildup at the beginning
decay: decrease in sound at the end
outer ear
pinna, auditory canal & the ear drum (tympanic membrane).
pinna - what we call the ear
funnel sound to other apparatus
carry sounds to tympanic membrane - thin sheet of skin
vibrates in time with incoming sound waves
middle ear
3 tiny bones called ossicles: articulate with ear drum
malleus + incus connect to drum acts like lever
stapes: connect to inner ear amplified energy
middle ear
large surface area for tympanic membrane concentrated to small area of stapes
air in outer + inner ear need to be translated into energy in cochlear fluid - need amplification
pushing motion of stapes into cochlear
middle ear
fluid changes in terms of pressure
pressure alleviated through bulging windows
inner ear
where auditory transduction takes place:
‣stapes pushed on oval window of the cochlea
‣round window bulges out with pressure from the stapes
bulging of round window
inner ear
scala vestibuli + scala tympani connected like bended tube
shift in water that travels all way around
cochlear partition separates scala vestibuli & scala tympani
inner ear
cochlear filled with fluid
snail shaped
3 parallel canals
scala media (not visible): tiny space between 2 canals - triangular shaped canal all the way through cochlear
inner ear
producing wave of fluid for pressure to be relieved at round window
base is closer to ossicles
scala media is affected - important bits happening here
organ of corti
structure on the basilar membrane composed of hair cells & dendrites of auditory nerve fibres
on basilar membrane - bottom half of partition
organ of corti
As the bulge passes by, the basilar membrane moves up & down causing the tectorial membrane to shear across the cochlear partition
movement gets translated to signals on organ of corti
exact point of transduction
Cilia
outer hair cells are embedded in the tectorial membrane
attached to portion where 3 media, but floats on top of hair cells
tectorial membrane moves up and down and moves hair back and forth
Scala media
filled with endolymph, fluid with high concentration of K+
Tip links
tiny filaments that stretch from tip of 1 cilia to side of its neighbor
tiny little coils - as they move across, longer hair cell pulls open ion channel
resting -70 mV, more K outside, so increase membrane potential as they move in tip links
mechanoelectric transduction
Shearing during upward displacement of cochlear partition mechanically opens ion channels:
K+ floods in, depolarizes cell, neurotransmitter released, action potential in auditory nerve
mechanoelectric transduction
super fast - don’t have to wait for cascade of processes - near instantaneous depolarization
incredibly sensitive - ion channels open with 1 nm movement of cilia
location coding in the cochlea
Diff parts of the cochlear partition are displaced to different degrees by different sound wave frequencies
narrower at base + widest at apex
location coding in the cochlea
bulge from stapes produces a travelling wave
peak of the wave’s envelope varies based on frequency
where cochlear partition most displaced, most basilar membrane movement, most hair cell activation
peak depends on sound itself
cochlea
tonotopically organized:
‣base: high frequency
‣apex: low frequency
perceptually similar frequencies located adjacent locations on membrane
base is narrower - high frequency sound more represented at thin areas
base is stiffer than apex - low frequency more likely to get all the way down to apex
frequency tuning curves
plot threshold of a cell in response to sound waves with varying frequencies
like orientation tuning curves
vary threshold to find minimal intensity to fire
can do that for diff cells across basilar membrane
frequency tuning curves
frequency with lowest threshold for cell is characteristic frequency
can do this curve for A1 + auditory nerves also
What do these tuning curves tell you about the relationship between frequency & threshold?
plots for a bunch of neurons, location is quite consistent
threshold for firing mirrors thresholds for detection
physiology matches perception
What do these tuning curves tell you about the relationship between frequency & threshold?
Similar frequencies produce similar peaks in the envelope, but we can discriminate them
Outer hair cells expand & contract in response to motion & efferent signals.
What do these tuning curves tell you about the relationship between frequency & threshold?
changes in shape affect basilar membrane - make it more stiffer
increase ability to distinguish peaks, sharpens localization
What do these tuning curves tell you about the relationship between frequency & threshold?
can be controlled at top down manner: auditory attention can be applied to particular pitch + frequency
in trying to isolate sound - increase in sensitivity for those pitches
Phase locking
auditory nerve fibres fire in synchrony with rising & falling pressure of pure tones
motion of cilia - as it moves to right - burst of activity in auditory nerve - corresponds to peak of sound wave
if it fires 100x per second, can infer it’s about 100 Hz
Phase locking
temporal limits on neurons upper limit of action potential 1000/s effective up to about 1000 Hz for high frequency sounds, neurons can’t keep up over 4/5000, no phase locking - kind of
Volley Principle
neurons take turns firing in phase
each individual nerve doesn’t have to fire more than 1000, across several neuron can get phase locking
auditory nerve fibers with high frequencies can get low pattern frequency in response by phase locking
Complex tone: 200Hz + 1600Hz
Neurons with high characteristics frequencies will code high frequency component (location coding) & will fire in phase to code the low frequency component (temporal coding).
neurons will fire in phase with 200 Hz to represent both high + low frequency sound
tonotopic organization preserved into A1
auditory nerve - cranial nerve VIII: synapses with cochlear nucleus
cochlear nucleus - in the medulla: neuronal specialization for coincident sounds, for frequencies, lateral inhibition to sharpen tuning, some just pass it on
tonotopic organization preserved into A1
superior olivary nuclei - in the pons: inputs from both ears converge (bilateral representations of sound) to compare sounds to determine timing
inferior colliculus - in the midbrain: reflexive head & eye-movements in response to sound
similar location + function - map location
tonotopic organization preserved into A1
medial geniculate nucleus - in the thalamus: sends + receives information from A1
gets more efferent signals compared to afferent
tonotopic organization preserved into A1
we need to know pathway*
describe parallel with vision in terms of function* on exam - in subcortex + primary visual and auditory cortex
tonotopic organization preserved into A1
lateral colliculus - superior colliculus
lateral + medial geniculate nucleus - more efferent
retinotopic + tonotopic organization
auditory system
hierarchically organized in the same was as the visual system.
A1belt areaparabelt area
A1 - simple features + sounds
surrounded by belt area
surrounded by parabelt
increasing complexity - association cortices - human speech, nonhuman sounds
auditory system
But a large proportion of auditory processing is done before the cortex.
evolution - audition is an older sense - evolved to use perceptual processes under low lighting condition
things that evolve first tend to be subcortical
audition
medium distance sense vision is far distance audition comes from stimuli in immediate vicinity if dangerous, faster the better subcortical is fast cortical lots of detail but slow
Auditory space
refers to the perception of where sounds are located in space:
‣ azimuth ‣ elevation ‣ distance
Auditory space
azimuth: left/right
elevation: up/down
distance: how far away
cues to estimate location of object in space
already represent frequency
Binaural cues
location cues that involve both ears
similar to binocular cues
interaural time differences
The smallest detectable interaural time difference is 20 μs (1/500,000 sec), corresponding to ~ 1° in space.
if coming from left, it reaches left ear first
time diff detectible is 20 microseconds
interaural time differences
directly in front + behind - reaches ears exactly the same time
left - reaches right ear 640 microseconds later
can’t tell if sound is in front or the back
interaural time differences
Sound is more intense at the ear closer to the sound.
more intense at ear closest to the sound
directly in front + behind diff is 0
interaural time differences
The disruption of sound waves creates a decrease in sound intensity on the far side of the head, called the acoustic shadow.
in part produces interaural level diff
long wavelengths of low frequency sounds are capable of bending around the head
interaural time differences
greater shadow for low frequency sound
localize low frequency sound better
There are two places in the azimuth where ITD & ILD are zero.
can’t tell if directly in front or behind
interaural time differences
won’t tell diff from those matching locations
60 degrees front left/right + 120 degrees behind
function of the distance between 2 ears
can’t tell diff anywhere along the cone motion
interaural time differences
There are many paired locations in the azimuth where ITD & ILD are exactly the same.
Cones of confusion
region of positions in space where all sounds produce the same time & level differences
same distance from ear - anywhere on the edge of these cones - location is not differentiable based on time diff or interaural level diff
the angle doesn’t matter - inficite number of cones of confusion
Cones of confusion
so move your head
as soon as you move your head, you can get time diff + interaural level diff
2 cones of confusion only matches up at 1 location
monaural location cues
sounds with the same ITD & ILD at different elevations produce different frequency spectra.
spectral shape cues, depend on how pinna modifies sound across spectrum
monaural location cues
folds produces changes to spectrum as function of elevation
alter diff frequencies in sound
mess with the shape of the pinna, mess with localization in elevation
monaural location cues
messing with elevation - use pure tones
shape of spectrum single line for pure tones - crap at localizing elevation of pure tones
Inverse-square law
distance from the source increases, intensity initially decreases much faster than distance increases
‣ decrease = 1/d2
only useful for comparing sounds that are known or familiar
more distant, the worse the accuracy, limit how useful inverse square law is going to be
judging distance
With distance, the spectral composition changes: Sound absorbing qualities of air dampen high- frequency sounds more than low-frequency sounds, changing timbre.
judging distance
high frequency sound attentuated more farther away - change in timbre of sound
crack of thunder can become a boom from far away
atmospheric perspective - attenuating certain frequencies of light
useful for really far away km or more
judging distance
Distance can be evaluated base on a ratio of direct & reverberating (indirect) energies.
compare ratio to recognize distance
auditory scene analysis: separating sources of sound
We can separate sources of sound based on their location in space.
allows us to identify diff sources of sound within the same environment
segragate source of sound
coming from diff locations
breaks down when coming from single source - speaker - yet still can separate sources
auditory scene analysis: separating sources of sound
We can separate sources of sound based on onset time.
same beep, but unlikely that they have same onset time
off even just a little bit
20 microseconds sufficient to segregating sound
auditory scene analysis: separating sources of sound
We can separate sources of sound based on auditory continuity.
often produced by same source
fill in gap of white noise with frequency they heard before
even with continuing change of frequencies - fill in gap
similar to good continuation
using simple sounds, but same effect with speech
auditory scene analysis: separating sources of sound
separate sources of sound based on timbre & pitch.
same fundemental frequency but diff timbre even at same note
same timbre - organize based on frequency
auditory scene analysis: separating sources of sound
We can separate sources of sound based on experience.
mixture - doesn’t allow you to seperate target from distractors
experience can help segregate sounds
adding even just 1 more distraction sound, find target
more distractors, the easier it is to identify target
melodic schema
representation of a familiar melody stored in memory
easy to tell diff between the melodies
