Hearing system Flashcards
1
Q
What are soundwaves?
A
• Soundwaves is energy transduced through the air by compression and rarefraction
2
Q
What is particle displacement a function of? Describe
A
o Particle displacement is a function of frequency
Low frequency- significant movement of molecules
High frequency- small movement of molecules in the air
3
Q
Does density of medium influence how sound propagates?
A
• Sounds propagates through the air in relation to the density of that medium
4
Q
What is the speed of sound in air?
A
o Air- 331 m/s
5
Q
What is the speed of sound in water?
A
o Water- 1380 m/s
6
Q
What is the speed of sound in bone?
A
o Bone- 2832 m/s
7
Q
What is period measured in?
A
o Period (T): seconds
8
Q
What is wavelength?
A
o Wavelength (I): metres in 1 cycle
9
Q
What is phase?
A
o Phase: 360o= 2π radians
10
Q
What is pure tone?
A
Sinusoidal/periodic change in pressure
11
Q
What is frequency?
A
o Frequency: Hertz/cycles per second
12
Q
What is the range of frequency that humans can hear?
A
Humans can hear 20 Hz-18kHz
13
Q
What is the perceptual correlate of frequency?
A
Pitch
14
Q
What is the nonlinear just noticeable difference concept of sound for frequency?
A
Nonlinear just noticeable difference (JND)- roughly logarithmic
• If have tone at low Hz range, can tell differences between tones differing from 1 Hz a lot more easily than if tone is at high Hz range
15
Q
What is amplitude?
A
o Amplitude-amount by which rarefraction and compression is occurring/power and intensity conveyed by energy wave propagated
16
Q
What is the perceptual correlate for amplitude?
A
Loudness?
17
Q
What range of amplitude that humans can hear?
A
1:10^6 pressure range for humans
18
Q
What is the just noticeable difference for sound amplitude? Describe
A
JND(just noticeable difference) is log10 intensity (I=P2) or dB= 20xlog10(P/Pref) where Pref=20uP (hearing threshold)
• Pref is roughly the average person’s hearing threshold at about 4 kHz (quietest sound that humans can hear)
19
Q
What does absolute threshold of hearing vary with?
A
Frequency
20
Q
Describe the pressure needed to deliver individual frequencies in humans as frequency increases
A
- Pressure needed to deliver individual frequencies decreases as humans go from 10Hz to 4-5 kHz from about 80dB to 0dB
- As sounds go above 4-5 kHz, increase in sound level dB is needed as absolute threshold increases
21
Q
What is the absolute threshold of hearing dependent on in humans?
A
• Highest threshold is dependent on age
o Upper threshold decreases with age
22
Q
What happens if sound pressure becomes too high?
A
o If pressure becomes high enough, percept is not one of sound but of pain
o Speech and music are in the middle of threshold of hearing and threshold of pain
23
Q
Does absolute sound threshold have a linear relationship with frequency?
A
• Non-linearity of threshold is important
24
Q
At what frequency are humans most sensitive?
A
• Humans are most sensitive to sounds around 4-5 kHz
25
What is the ear made of?
• Ear is made of 3 components
o Outer ear
o Middle Ear
o Inner ear
26
What are the components of the outer ear?
Components-
• Pinna
• Concha
• Auditory canal (which is terminated medially by the ear drum)
27
What is the function of the outer ear?
• Complex filtering of the sound as a function of location (direction of arrival of the sound)
28
How does the outer ear filter complex sounds?
o No uniform transduction of frequencies across the full range of hearing as a function of location-> sound is being filtered by the complex convolutions of the outer ear
There are a variety of acoustic mechanisms used to boost sound in some frequencies for some directions, and attenuate the sound in other frequencies for some directions such as refraction, partial resonance and destructive interference
• This changes as a function of the angle of incidence of the sound wave striking the outer ear
29
What perceptual cues does complex filtering of the sound by the outer ear provide?
o Complex filtering of the sound provides important perceptual cues that the brain uses to do two things:
Externalisation
• Percept of sound outside our heads is a consequence of it being filtered by the outer ear
Localisation
• Filter function changes as a function of a location-> works out where the sound is coming from
30
What are the components of the middle ear? Describe the role of each component
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Components-
• Starts at eardrums
• Middle ear bones and muscles
o Conveys motion of ear drums into the inner ear/cochlea
o Bones:
Malleus
• Footplate of malleus attaches to tympanic membrane
Incus
Stapes
o Muscles:
Stapedius
• Attached to stapes
Tensor tympani
• Attached to malleus
• Eustachian tube
o Runs from middle ear into the nasopharynx
o Used to equalise pressure in middle ear space to that in the external environment
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31
What problem would arise if the middle ear did not exist and only the outer ear and inner ear remained?
• Problem: impedance mismatch between the outer and inner ears-gas/fluid interface
o Transduction apparatus (hair cells) are bathed in fluid inside the inner ear in the cochlear-> creation of air/water interface
Strike of energy at air/water interface produces an impedance mismatch which will cause 99% of the energy to reflect back off the liquid layer
32
What is the function of the middle ear?
* The middle ear is an impedance transformation-> overcomes air/water barrier ->allows for detection of very quiet sounds
* The middle ear acts as a band pass resonator
Increased stiffness increase Fres and bandpass
• Protective role
• Decreases low frequency masking
33
How does the middle ear act as an impedance transformer?
o Three key mechanisms
Ratio Tympanic Membrane: oval window areas
• Large area in which energy is being collected (tympanic membrane) and a smaller area over which energy is being delivered into inner ear-> gives rise to increase in force and pressure delivered into the fluids of the cochlea
Lever action of middle ear bones
• Large movements of umbo of malleus translate into smaller but more forceful movements of the stapedius
o Stapedius is sitting on round window of the cochlea and is able to apply significantly more pressure/force into the fluids of the inner ear
Buckling motion of tympanic membrane
• Gives mechanical advantage to the rate at which the umbo of the malleus can be accelerated
34
What is resonance and what is it determined by?
o Resonance- response of a system to a driving force
Determinants of resonant frequency both oppose motion and are out of phase
• Mass
o Inertia= mass x acceleration
• Stiffness
35
What happens to mass and stiffness at resonant frequency?
At resonant frequency (Fres) mass and stiffness effects cancel out
• When driving force= Fres, the system responds maximally-> maximum amount of movement
36
What resonant frequency does a large mass and low level of stiffness result in?
Large mass and a low level of stiffness= low resonant frequency
37
What resonant frequency does a small mass and a high level of stiffness result in?
Small mass and high level of stiffness= high resonant frequency
38
What does damping resistance determine?
Damping resistance determines sharpness of tuning (Q) and time constant (t)
39
What does positive damping due to response?
• Positive damping reduces amplitude of response
40
What does negative damping do to a response?
• Negative damping produces increased motion of system and much sharper tuning around resonance frequency of system
41
What happens to resonance frequency when there is a lot of damping?
• Where there is a lot of damping (very viscous), resonance frequency is relatively low compared to when there is no damping
42
What components of the middle ear allow the middle ear to act as a band pass resonator and how do these components function? What does action of these components result in?
o Middle ear is a mechanical system- has certain amount of mass (bones) and has certain amount of stiffness (joints between bones and stiffness of tympanic membrane
Due to specific mass and specific fitness, middle ear resonates at particular frequency
Changes in stiffness (or mass) shifts the frequency of resonance up in frequency
o Tensor timpani and stapedius muscles increase stiffness which increases frequency
Allows for increase in mid frequency transmission but decrease in low frequency transmission
o Relaxation and contraction of tensor timpani and stapedius muscles allows humans to hone in on quiet sounds
o Eustachian tube: vents middle ear via nasopharynx
Can open and close
Middle ear pressure is differential and can increase tympanic membrane stiffness
43
What happens before you shout loudly and why?
Before you shout loudly, muscles contract and shift bandpass characteristics of middle ear up so that the enormous amount of volume made doesn’t damage the inner ear hair cells
44
How does tinnitus occur?
In young children, eustachian tube can become blocked due to mucus
• Cells that line the middle ear (mucosa) absorb the oxygen and get development of negative pressure inside the middle ear
o Tympanic membrane is bulging inwards into the middle ear-> increases stiffness in middle ear and shifts bandpass characteristics
o As negative pressure build up, exudation of extracellular fluids from the mucosa into the middle ear which starts to build up and facilitates bacterial reproduction (tinnitus)
45
What cranial nerve innervates the tensor tympani and by what bone is it affected?
Tensor tympani (CNV)-> malleus
46
What cranial nerve innervates the stapedius and by what bone is it affected?
Stapedius (CNVIII)-> stapes
47
What is low frequency masking and why is it a problem?
• Decreases low frequency masking
o The way in which individual axons in the auditory nerve transduce the sound and sensitivity to frequencies- more sensitive to low frequencies
Loud low frequency noises can interfere with our ability to understand middle and upper frequencies
48
What can dysfunction of the middle ear lead to? Give examples of dysfunction
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Dysfunction of middle ear leads to conductive hearing loss
• Dislocation of middle ear bones
• Tearing of ear drum
• Filling of middle ear
• Changes in pressure
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49
What are the components of the inner ear?
Components-
• Cochlea
• Semicircular canals
• Vestibular system
50
Describe the sensitivity of the cochlea
• Cochlea is an optimally tuned analyser
o Low damping but high frequency selectivity
o Very high sensitivity and frequency resolution
o Very high temporal resolution
51
Describe the connections in the inner ear
• Afferent: from inner ear to CNS mediated by spinal ganglion
• Efferent: from the CNS into the inner ear-
o Principle component of this efferent system is COCB (Crossed Olivo Cochlear Bundle)
Play an important role in the level of sensitivity that are able to be achieved with the coding in the cochlea
• Cochlea is innervated by the auditory nerve (CNVIII)
52
Describe the anatomy of the cochlea
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o Three different components
Scala vestibuli
• Contains perilymph
Scala tympani
• Contains perilymph
Scala media
• Contains cochlear duct which is bathed in endolymph
• Stria Vascularis
o Highly metabolic cells on the scala media wall
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o Basilar membrane
Tough membrane separating scala media from scala tympani
53
Describe the composition of endolymph
o Endolymph- very high in potassium concentration: +80mV electrical gradient from the endolymph into the hair cells
Inner hair cells innervated by auditory nerve
54
What is the purpose of the stria vascularis?
• Stria Vascularis
o Highly metabolic cells on the scala media wall
Secrete high levels of potassium into the endolymph
Feedback mechanism to ensure maintenance of high electrical gradient-> maintains sensitivity of the apparatus
55
Describe the pressure pathway through the cochlea/ what happens after stapes movement on the oval window in the cohlea
• Pressure pathway through cochlea
o After stapes movement on the oval window, pressure builds in scala vestibuli which is:
Transmitted into the scala media, causing the basilar membrane to bend and increasing the pressure in the scala tympani
• Upward and downward motion of the basilar membrane (which the transduction apparatus sits on top of)
Transmitted in the perilymph from the scala vestibuli to the scala tympani
o Results in outward bulging movement of round window
56
What is the composition of the organ of corti?
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• Consists of
o Basilar membrane
o Tectorial membrane
Attached at one end but free at the other
o Stereocilia
1 row of inner hair cells
• Loosely wave under tectorial membrane
3-5 rows of outer hair cells
• They stick into gelatinous portion of tectorial membrane
• 3 rows in humans
o Supporting cells
o Nerve fibres
o Spiral ligament
Tectorial membrane, basilar membrane and supporting cells are anchored at spiral ligament
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57
What is the tallest stereocilia called?
o Kinocilium is the tallest stereocilia and has a bulge sitting at the top
58
How are stereocilia ordered?
o Ordered by height
59
What is a tip link on stereocilia?
Stereocilia attached to each other by tip link- a thread originating from top of shorter hair cell to taller hair cell
60
What is the cuticular plate on the hair cell?
Cuticular plate
• Where hair cell extremities are located
• Tight junctions between cuticular plate and basal membrane
61
What is the transduction apparatus in the body of the hair cell?
Transduction apparatus
• With afferent and efferent nerve ending
o Afferent nerve ending sends signals towards CNS
o Efferent nerve endings can modulate the level of polarisation of the hair cells itself
62
Describe the opening and closing of the stretch mediated ion pores when:
- The hair cells are pushed towards the kinocillium
- The hair cells are pushed away from the kinocillium
- The hair cells are at rest
o If hair cells pushed towards kinocilium, there is increase in tension of tip links and an increase in tension of ionic pore in tip of stereocilia
Stretch mediated ionic pore opens and there is depolarisation in hair cell
o If hair cells pushed away from kinocilium, there is a decrease in tension of tip links and ionic pores are closed -> no depolarisation occurs
o At rest, some ionic pores are open but majority of pores are not open
63
Describe how tip links on he stereocilia facilitate sensory transduction
o Tip links attach to mechanical pores at tip of stereocilia
Stretch mediated ionic pore increases potassium conductance at tip of stereocilia
o The resting membrane potential changes with deflection of the sterocilia
64
What enables the sensitivity to deflection of the stereocilia? Is this sensitivity the same in every direction of stereocilia movement?
o High electro-chemical gradient from endolymph to hair cell results in extraordinary sensitivity to deflection of the stereocilia
Sigmoidal and asymmetrical input/output function
Depolarisation/activation function caused by opening of stretch mediated ionic pores occurs at a faster rate than the hyperpolarisation caused by closing of the stretch mediated ionic pores
65
What can block transduction channel in the tips of the stereocillia?
Aminoglycoside
66
What produces stereocillia movement in the cochlea and what is the consequency of this?
* Pressure moving from stapes footplate across cochlea layers causes the basilar membrane to move in an upward-downward movement
* This causes tectorial membrane, which is only anchored to the spinal ligament at one point, to move up and down which causes a upwards and downwards deflection of the stereocilia
* This produces a modulation of receptor resting potential and activation of spiral ganglion cells and auditory nerve fibres
67
How does sensory transduction using stereocilia?
• Tiplinks between adjacent stereocilia cause stretch mediated ion pores to be open when movement is towards kinocilium
o Only a small deflection is required
• This produces an inrush of potassium into the stereocilia and into the body of the hair cell
• This causes an influx of calcium into the hair cell
• Influx of calcium leads to release of glutamate neurotransmitter by basal synapse, activating the spinal ganglia
68
What is the temporal code?
• Temporal code- manner of encoding frequency by cochlea
69
How does the temporal code work?
o At low frequencies, depolarisation and repolarisation faithfully reflect sinusoidal variations in pressure
At low frequency, there is a frequency of oscillation that is locked at frequency of stimulation (phase lock)
• Each depolarisation of the hair cell leads to a burst of glutamate, making an action potential
• Action potentials become phase locked to low frequency stimuli
Auditory system counts the rate at which action potentials are propagating up to auditory nerve to know frequency of stimulation
• Timing of action potentials associated with AC component
• Phase locking falls off at mid to high frequency
70
At what frequencies does temporal code no longer work and why?
o At high frequencies, membrane potential no longer reflects fluctuations produced by stereocilia
This is due to asymmetrical input-output function which results in AC and DC components in the receptor
• Increase in d.c. component is instead apparent (at 1.5-2 kHz frequency)
• Decrease in AC component as AC component is filtered out by the low pass characteristics of the receptor membrane
o Arrangement of the capacitance and resistance of the bilipid membrane layer is such that it acts as a low pass filter
Lets low frequencies through but not high frequencies
71
Is temporal code insensitive or sensitive to the intensity dB level?
• Relatively insensitive to stimulus/intensity dB level
72
What is Fourier's theorem?
• Fourier’s theorem
| o Complex sounds can be decomposed into a series of pure tones
73
What is fast fourier transform analysis?
Fast fourier transform analysis is a mathematical method for transforming a function of time into a function of frequency
• Frequency on x axis, amplitude on the y axis
74
What rules do the spectral elements in naturally resonating objects follow?
• Natural sounds have harmonic components-
o A naturally resonating object will have many different spectral elements in its complex structure but follow rules in terms of how harmonic components relate to fundamental frequency
Components are all at frequencies that are whole number multiples at the fundamental (lowest) frequency
75
How are frequencies mapped along the cochlea?
• Mapping of frequency along length of cochlea-
o Apical end of cochlea (end furthest away from input energy) is mostly sensitive to low frequencies
o Basal end of cochlea (near stapes) is mostly sensitive to higher frequencies
76
What is the cause of this variation in resonance frequency along the basilar membrane?
Structural variations of the basilar membrane from base to apex
• Stiffness of the basilar membrane changes from base to apex
• Variation in mass loading of the fluids from bass to apex
• Position of maximum displacement on the basilar membrane varies as a function of frequency content of the stimulating sounds
77
How do variations in the stiffness of the basilar membrane result in the variation in resonance frequency along the basilar membrane?
• Stiffness of the basilar membrane changes from base to apex
o Stiffness is highest at the base of the cochlea and lowest at the apex
o As decrease stiffness, resonance changes from high frequencies (basal end) to low frequencies of resonance (apical end)
78
How do variations in the mass loading of the fluids of the basilar membrane result in the variation in resonance frequency along the basilar membrane?
• Variation in mass loading of the fluids from bass to apex
o When there is high stiffness and high frequency, low mass of fluid (mass loading is low) has to be moved to produce change in the movement of round window in contramotion to oval window
High stiffness and low mass contributes to high resonance frequency
o When there is low stiffness and low frequency, high mass of fluid (mass loading is high) has to be moved to produce change in the movement of round window in contramotion to oval window
Low stiffness and high mass contributes to low resonance frequency
79
What is the traveling wave in the cochlea?
o Traveling wave-Appearance of wave moving down the cochlear duct: represents change in phase of motion of the membrane dependent on the frequency and differences in resonances
80
What is the frequency place code and how does it work?
Frequency place code
• Inner hair cells indicate the place (frequency) of stimulation
• Hair cells at a particular location on the basilar membrane are going to be excited by motion at a local area, giving rise to activation of axons from CNVIII that are innervating that portion of the basilar membrane
o Auditory system looks at which CNVIII axon is excited knowing where in the basilar membrane that axon innervates-> indicator of frequency
81
What is magnitude of movement along the basilar membrane related to?
o Pattern of activation along basilar membrane where magnitude of movement will be related to the extent of the energy at particular frequencies
More activation= more intense movement of basilar membrane
Less activation= less intense movement of basilar membrane
Ensemble code gives rise to place code of frequency that is transmitted into the auditory system
82
What is the characterised frequency in the auditory nerve?
• Characterised frequency- frequency at which CNVIII axon needs minimal sound level for activation and corresponds to precise place where axon is sitting on basilar membrane
83
What is the inner hair cell connected to?
• Inner hair cell connection to the VIIIth nerve-> ordered projection into the CNS
84
Describe tuning curve peaks as frequency increases/decreases
• Sound spectrum coded by family of tuning curves of auditory nerve:
o Sharply tuned ‘tip’ but broadens at high stimulus levels
Topographically organised high to low frequency reflects innervation of basilar membrane
• At high frequency, tuning curves have very sharp tips and are sharply tuned
• At low frequency, tuning curves are broadly tuned: hard to determine precise frequency of stimulation
85
What does tuning come from?
Tuning comes from extent of activation of inner hair cell on basilar membrane
86
Is place code of frequency insensitive/sensitive to stimulus intensity?
Sensitive to stimulus intensity dB level
| • Degradation of frequency tuning with an increase in overall stimulus level
87
Describe the preservation of topographic organisation throughout the auditory system
• Topographic (place code) organisation of frequency preserved in structures of auditory pathway up to primary auditory cortex
o Systematic change in cortical fields across nuclei a place code of frequency
In higher cortical areas, strict coding of frequency tends to break down
88
Describe how frequency coding occurs in the auditory system
* Temporal code- based on phased locking of receptor potential only effective at lower frequencies
* Place code for mid to high frequencies- based on resonance and bandpass filtering on basilar membrane and ordered topographical projection of VIIIth nerve
* Temporal code used at frequencies below 1.5kHz but place code used at frequencies above 1.5 kHz
89
What is the implication that there is only passive tuning in post mortem cochlea?
• Passive tuning revealed in post mortem cochlea reveals that mechanical characteristics are only a part of cochlea tuning processes-> less sensitive to sound when animal is euthanised than when it is alive
o Physiologically vulnerable process in tuning (ototoxic drugs and hypoxia also cause blunt tuning)
90
How is the cochlea actively tuned physiologically?
• Very sharp tuning suggests physiologically active negative damping (put energy in system) in cochlea
o Otoacoustic emissions- evidence for negative damping
Both spontaneous and evoked otoacoustic emissions indicate that energy is being pumped into the motion of the basilar membrane (negative damping)
• Basilar membrane is creating energy that is being pumped back through transduction chain of middle earbones to eardrum
91
What structure actively pumps energy into the basilar membrane and what is the evidence supporting this?
o Evidence that outer hair cells pump energy into the basilar membrane
Patterns of efferent innervation
• When stimulate crossed olivcochlear bundle, fine frequency tune of the inner hair cells are disrupted and there is modulation of basilar membrane selectivity
o Crossed olivocochlear bundle is connected to outer hair cells
• Selective lesions of the outer hair cells eliminates very sharp tuning and sensitivity of inner hair cells/auditory axons
• Outer hair cell rhythmic motility when current is injected: outer hair cells inject energy and increase the tuning
92
What are the biological functions of the auditory system?
• To detect and analyse biologically interesting sounds-paraphonic detection system
o Spectro-temporal analysis of stimulus ‘features’
o Work out where sound comes from
o Focus on desired sound
93
Why is segregation and streaming of auditory objects needed?
o Sounds almost always occur against a background
94
Why are superimposed sounds a problem for hearing?
• Multiple concurrent sounds means superposition of excitation in the inner ear
o Brain needs to sort out the frequency correlated with the specific sound
95
How does the brain deal with superimposed sounds?
Segregating and regrouping
Identification
Localisation of sound
96
What features of sound and laws of sound does the inner ear segregate and regroup multiple concurrent sounds?
• Primitive grouping: fundamental perceptual processes which exploit the statistics of the sound
o Event boundaries: onset and offset synchrony of the components
Group of frequencies that either all turn off at the same time or all turn on at the same time-> likely that frequencies come from same object
o Common temporal modulation of amplitude and frequency
o Periodicity- F0, harmonicity, fine structure periodicity
Harmonicity- How spectral components relate to fundamental frequency -> whole number multiple relation probably means they are from a common sound
Structures with periodicity will also display temporal structure
o Continuity and similarity
Increases and decreases in gain of different spectral components -> continuity of modulation and progressive change also indicates that it is an individual sound
97
What parts of the brain are responsible for segregating and regrouping superimposed sounds?
• Bottom-up/stimulus driven automatic process:
| o Processing from brainstem, midbrain and superior temporal gyrus
98
What features does the ]ear use to localise sound?
• Auditory system compares differences in soundwave in each ear and locate where a sound is in space
• Binaural cues to sound location (duplex theory of auditory localisation)
o Interaural time differences
o Interaural level differences
• Filter functions of the outer ear
• Combination of interaural time differences, interaural level differences and differential filtering of the outer ear that determines sound localisation
o Spectral cues that resolve the cones of confusion
99
What are interaural time differences and when are they most effective?
o Interaural time differences
Sound from a particular source reaches two ears at differing times due to path length differences to each ear
• Can detect interaural time differences from minimum 10-20 us to 600-800 us at maximum interaural time differences
Most effective at low frequencies (due to phase locking ability)
100
What are interaural level differences and when are they most effective?
o Interaural level differences
Sound in the near ear is louder than sound in the far ear (far ear is shadowed)
Effective for mid to high frequencies when the dimensions of the head are equal/larger than dimensions of the sound wave
101
Describe the cone of confusion problem in hearing and how it is solved
o Binaural cue ambiguity and cone of confusion problem
Sounds from different directions but of the same interaural time/level difference would provide the same result
This is solved by the filter functions of the outer ear
102
Why are the filter functions of the outer ear useful?
• Filter functions of the outer ear
o In cone of confusion where interaural time/level differences would be the same, there are differences in how the outer ear filters the sound
Differential filtering produced by the outer ear dependent on the location that the brain uses to resolve where sound source is located
103
How does the auditory system group together different spectral components that are likely to have originated from the same source and why?
• The auditory system has evolved to group together different spectral components that are likely to have originated from the same source
o Identification of a sound’s fundamental frequency, due to the law that spectral elements of a singular sound are whole multiple multiples of that fundamental frequency, allow for grouping of the different spectral components
o This process of segregating out, using physical rules of the way that sound objects create the spectra that they do, allows the brain to focus on sound, bind the spectral elements together and make a perceptually auditory object
Perceptually an auditory ‘object’ usually corresponds to a single sound source
104
What spectrum do transient sounds have and why?
o Transients as a crucial (evolutionary) class of sounds have a flat and broad spectrum
105
What do spectral cues require and when is it hard to determine filter characteristics?
• Spectral cues require broad bandwidth sounds and the proximal spectrum is unknown
o Without knowing what the proximal stimulus is, it is difficult to work out what the filter characteristics are
106
How is sound localised within the cone of confusion when spectral cues are not available?
• Localisation as a dynamic behavioural process
o Head rotation resolve the cones of confusion as change in relative rotations changes the magnitudes of interaural time differences/interaural level differences of the sound
ww
107
Is ear morphology constant as we age? What does this affect and how does the brain deal with this?
• Ear morphology can change substantially over time and age
o Precise filtering by the outer ear is dependent on physical structure of the outer ear
o Changes in physical features of outer ear results in changes to spectral cues
• Brain in the course of development calibrates to individual’s outer ear
o The auditory system can continually relearn new cues
108
Describe the effect of insertion and removal of pinna moulds on sound localisation
Pinna moulds change filtering-> at first, localisation of sound is difficult but over time people get better at localising sounds with the pinna mould (recalibration)
• However, when pinna moulds are removed after a long period of time, there are no aftereffects of the pinna mould adaptation in sound localisation abilities
109
Describe the spatial and non-spatial auditory attention system (functional anatomy)
• Analysis of complex scenes through auditory attention-
o Attention on frequency/ pitch activates the superior temporal gyrus
o Attention on spatial characteristics of sound activates the frontal eye fields
• There is a spatial and non-spatial attention system
110
What does robust localisation of sounds depend on combining?
• Robust localisation of sources based on combining
o Binaural cues (ITD and ILD)
o Spectral (pinna) cues
o Scanning head movements
