PSY280 - 8. Sound

Question 1

sound: physical definition

Answer 1

pressure changes in the air

how we detect + translate simple sounds and construct auditory scenes

Question 2

sound: psychological definition

Answer 2

our experience of the physical dimension

Question 3

Pressure changes

Answer 3

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

Question 4

Pressure changes

Answer 4

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

Question 5

Pressure changes

Answer 5

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

Question 6

sound waves

Answer 6

amplitude= loudness - higher the amplitude, louder sound
frequency= pitch - higher frequency,higher the pitch

Question 7

sound waves: units & limits

Answer 7

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

Question 8

sound waves: units

Answer 8

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

Question 9

sound waves: units

Answer 9

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

Question 10

sound waves: limits

Answer 10

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

Question 11

sound waves: limits

Answer 11

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

Question 12

Elephants

Answer 12

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

Question 13

Complex tones

Answer 13

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

Question 14

Pure tones

Answer 14

represent pressure changes that occur in perfect sine wave pattern
few sounds are ever this simple

Question 15

Fourier analysis

Answer 15

Sounds can be divided into component sine waves
Components are called harmonics
partial out diff sine waves of diff amplitude + frequency embedded in it

Question 16

spectrum

Answer 16

summary of the Fourier analysis

plot them on graph with frequency as x axis + amplitude as y axis

Question 17

fundamental frequency

Answer 17

lowest frequency harmonic

fundamental frequency in figure is 200, each subsequent harmonic is multiple of fundamental frequency

Question 18

harmonic spectrum

Answer 18

composed of harmonics that are multiples of fundamental frequency

Question 19

harmonic spectrum

Answer 19

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

Question 20

Pitch

Answer 20

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

Question 21

Timbre

Answer 21

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

Question 22

Timbre

Answer 22

based on differences in harmonics, attack & decay
buildup of sound over time
attack: buildup at the beginning
decay: decrease in sound at the end

Question 23

outer ear

Answer 23

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

Question 24

middle ear

Answer 24

3 tiny bones called ossicles: articulate with ear drum
malleus + incus connect to drum acts like lever
stapes: connect to inner ear amplified energy

Question 25

middle ear

Answer 25

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

Question 26

middle ear

Answer 26

fluid changes in terms of pressure | pressure alleviated through bulging windows

Question 27

inner ear

Answer 27

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

Question 28

inner ear

Answer 28

scala vestibuli + scala tympani connected like bended tube shift in water that travels all way around cochlear partition separates scala vestibuli & scala tympani

Question 29

inner ear

Answer 29

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

Question 30

inner ear

Answer 30

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

Question 31

organ of corti

Answer 31

structure on the basilar membrane composed of hair cells & dendrites of auditory nerve fibres on basilar membrane - bottom half of partition

Question 32

organ of corti

Answer 32

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

Question 33

Cilia

Answer 33

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

Question 34

Scala media

Answer 34

filled with endolymph, fluid with high concentration of K+

Question 35

Tip links

Answer 35

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

Question 36

mechanoelectric transduction

Answer 36

Shearing during upward displacement of cochlear partition mechanically opens ion channels: K+ floods in, depolarizes cell, neurotransmitter released, action potential in auditory nerve

Question 37

mechanoelectric transduction

Answer 37

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

Question 38

location coding in the cochlea

Answer 38

Diff parts of the cochlear partition are displaced to different degrees by different sound wave frequencies narrower at base + widest at apex

Question 39

location coding in the cochlea

Answer 39

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

Question 40

cochlea

Answer 40

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

Question 41

frequency tuning curves

Answer 41

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

Question 42

frequency tuning curves

Answer 42

frequency with lowest threshold for cell is characteristic frequency can do this curve for A1 + auditory nerves also

Question 43

What do these tuning curves tell you about the relationship between frequency & threshold?

Answer 43

plots for a bunch of neurons, location is quite consistent threshold for firing mirrors thresholds for detection physiology matches perception

Question 44

What do these tuning curves tell you about the relationship between frequency & threshold?

Answer 44

Similar frequencies produce similar peaks in the envelope, but we can discriminate them Outer hair cells expand & contract in response to motion & efferent signals.

Question 45

What do these tuning curves tell you about the relationship between frequency & threshold?

Answer 45

changes in shape affect basilar membrane - make it more stiffer increase ability to distinguish peaks, sharpens localization

Question 46

What do these tuning curves tell you about the relationship between frequency & threshold?

Answer 46

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

Question 47

Phase locking

Answer 47

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

Question 48

Phase locking

Answer 48

``` 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 ```

Question 49

Volley Principle

Answer 49

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

Question 50

Complex tone: 200Hz + 1600Hz

Answer 50

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

Question 51

tonotopic organization preserved into A1

Answer 51

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

Question 52

tonotopic organization preserved into A1

Answer 52

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

Question 53

tonotopic organization preserved into A1

Answer 53

medial geniculate nucleus - in the thalamus: sends + receives information from A1 gets more efferent signals compared to afferent

Question 54

tonotopic organization preserved into A1

Answer 54

we need to know pathway* | describe parallel with vision in terms of function* on exam - in subcortex + primary visual and auditory cortex

Question 55

tonotopic organization preserved into A1

Answer 55

lateral colliculus - superior colliculus lateral + medial geniculate nucleus - more efferent retinotopic + tonotopic organization

Question 56

auditory system

Answer 56

hierarchically organized in the same was as the visual system. A1belt areaparabelt area A1 - simple features + sounds surrounded by belt area surrounded by parabelt increasing complexity - association cortices - human speech, nonhuman sounds

Question 57

auditory system

Answer 57

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

Question 58

audition

Answer 58

``` 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 ```

Question 59

Auditory space

Answer 59

refers to the perception of where sounds are located in space: ‣ azimuth ‣ elevation ‣ distance

Question 60

Auditory space

Answer 60

azimuth: left/right elevation: up/down distance: how far away cues to estimate location of object in space already represent frequency

Question 61

Binaural cues

Answer 61

location cues that involve both ears | similar to binocular cues

Question 62

interaural time differences

Answer 62

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

Question 63

interaural time differences

Answer 63

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

Question 64

interaural time differences

Answer 64

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

Question 65

interaural time differences

Answer 65

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

Question 66

interaural time differences

Answer 66

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

Question 67

interaural time differences

Answer 67

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

Question 68

interaural time differences

Answer 68

There are many paired locations in the azimuth where ITD & ILD are exactly the same.

Question 69

Cones of confusion

Answer 69

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

Question 70

Cones of confusion

Answer 70

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

Question 71

monaural location cues

Answer 71

sounds with the same ITD & ILD at different elevations produce different frequency spectra. spectral shape cues, depend on how pinna modifies sound across spectrum

Question 72

monaural location cues

Answer 72

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

Question 73

monaural location cues

Answer 73

messing with elevation - use pure tones | shape of spectrum single line for pure tones - crap at localizing elevation of pure tones

Question 74

Inverse-square law

Answer 74

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

Question 75

judging distance

Answer 75

With distance, the spectral composition changes: Sound absorbing qualities of air dampen high- frequency sounds more than low-frequency sounds, changing timbre.

Question 76

judging distance

Answer 76

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

Question 77

judging distance

Answer 77

Distance can be evaluated base on a ratio of direct & reverberating (indirect) energies. compare ratio to recognize distance

Question 78

auditory scene analysis: separating sources of sound

Answer 78

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

Question 79

auditory scene analysis: separating sources of sound

Answer 79

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

Question 80

auditory scene analysis: separating sources of sound

Answer 80

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

Question 81

auditory scene analysis: separating sources of sound

Answer 81

separate sources of sound based on timbre & pitch. same fundemental frequency but diff timbre even at same note same timbre - organize based on frequency

Question 82

auditory scene analysis: separating sources of sound

Answer 82

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

Question 83

melodic schema

Answer 83

representation of a familiar melody stored in memory | easy to tell diff between the melodies