Week 7 Audition

Question 1

Audition Info

Answer 1

• Audition is a far sense
  o Sounds can travel long distances, through and around obstacles – can hear what’s on the other side of a wall
  o Gives us 3D, 360’ sensory information – can localise sounds
• Audition enables us to identify, locate and react to things in the environment and
  allows for verbal communication and music
  o Ability to speak relies on ability to hear yourself – modulate your muscles

Question 2

Auditory stimuli

Answer 2

• The stimulus for audition is acoustic energy = pressure changes in the molecules
  (medium) around us
  o Medium is most often gas but can be molecular movement in a liquid
  medium or even a solid
  o Steel has the fastest conductance of acoustic energy
• When an object moves, it creates a disturbance in the surrounding molecules/medium
  o Each molecule moves a bit, initiating movement in a nearby molecule
  o Creates a ripple effect
  o If this ripple of molecular disturbance reaches your ear, auditory receptors
  (hair cells) can detect this acoustic energy and the perception of sound can
  result
• You must have some sort of medium (some array of molecules ready to disrupt) to
  have sound
  o Robert Boyle’s alarm in a vacuum
   Suck air out of jar – sound goes away
   Everything mechanically was still happening in the bell but eliminate
  molecular disturbance to eliminate sound o Ridley Scott’s alien tag line
   Molecules are too far away from each other in space to disturb each other – no sound created
   Initial molecule moves but too far away from next one in line

Question 3

Sound waves

Answer 3

• Acoustic energy is visually represented as a sound wave, which illustrates the
  amplitude and frequency of molecular disturbance
• Two physical characteristics linked to 2 perceptual characteristics
  o Amplitude = displacement from baseline (y axis)
   Large disturbance in air molecules = large amplitude wave
   Gives loudness submodality
  o Frequency = distance between crests (x axis)
   High frequency disturbance in molecules = very frequent crests
   Gives pitch submodality

Question 4

Quantifying sound waves

Answer 4

o Amplitude
 Humans can perceive a huge range of amplitudes
 Expanded stimulus::intensity relationship
 Decibel (dB) scale – moves up amplitude in a log scale
 Loudness linked to amp of a sound wave given in dB
 Pain threshold ~ 140 dB
 Modality shift from hearing as sound to tactile pain
 Danger zone begins 80 dB for hearing loss
 Threshold for hearing is zero
 Human range for amp detection
 0 – 140 dB though is age dependent
 As you get older you lose bottom end of scale
o Frequency
 Humans can perceive a subset of frequencies
 Hertz (Hz) – has to be in the spectrum to detect
 Pitch linked to frequency of a sound wave given in Hz
 We don’t hear entirety of Hz spectrum
 Other animals can hear things we can’t
 Sensory system is limited in detection abilities
 Human range of detection
 20 to 20,000 Hz for young adults
o As you get older you lose the top end
o Have to talk low and loud for elderly to hear
 Emit high frequency sound the older adults can’t hear
o If loud enough is annoying to young people – move
away from area
o A noise that won’t annoy the adults – teen deterrent o 80dB bursts at ~17,000 Hz
o Use sound to exploit hearing range

Question 5

Acoustic energy hits objects

Answer 5

- Some of it is absorbed into the object
o Plaster/tile absorb ~3% o Carpet/drapery ~25% o Soft furnishings
- Some of it is reflected back as echoes
o Reflected echoes can be useful or annoying o Hard surfaces
o Sonar/echolocation
 Detect where you are in environment
 Humans use?
 Boats, depth/fishing fish finding navigation systems
 Submarine navigation
 Echolocation in the blind
o Medical imaging with ultrasound
 Reflect off bones
o Poor acoustics in concert halls

Question 6

Human echolocator

Answer 6

o An echolocator blind person listening to sound stimuli
 Visual cortex lights up as well as auditory cortex
 Open space when lost vision – utilised by hearing

Question 7

Anechoic chambers

Answer 7

o All sound waves are absorbed – none are reflected
o Hear only initial original source of sound
o Used to testing sound quality of audio equipment, sound emissions of
appliances, machines, etc.
o Semi-anechoic chambers are more common due to construction difficulties o Can be quite disturbing – can hallucinate, disorientate
 NASA uses to train astronauts for lack of sound in space

Question 8

Process of Hearing

Answer 8

1. Acoustic energy reaches outer ear (pinna)
   o Pinna functions to resonate and localise sound waves o We have two of them to better localise sound
    Can compute time difference or intensity difference between two sources – tell where sound came from
    Can function with just one but spatial acuity of sound affected
2. Resonates down auditory canal and hits tympanic membrane
   o Tautmembrane
   o Where middle ear starts o Membrane vibrates
3. Vibration of membrane transfers to series of ossicles
   o Malleusincusstapes
   o Middle ear
4. Stapes initiates vibration on oval window
   o Causes vibration in fluid-filled cochlea
   o Inner ear
   o Vibrations from air to fluid – moving fluid takes more energy than moving air molecules
5. Fluid movement disturbs basilar membrane of the cochlea
   o Causes bending of hair cells (sensory neurons)
   o Leads to signal transduction
   o Neuronal signal relayed to next neuron (axons contributes to CNVIII, auditory
   nerve)
6. Neural signal relayed to auditory fibres
   o These form CNVIII
7. Synapse in cochlear nucleus of medulla
   o Crosses to superior olive-inferior colliculus-thalamus-A1

Question 9

Why such a piecemental process

Answer 9

• To amplify the acoustic energy
• The cochlear medium is liquid – initiating pressure disturbances requires more
  energy
  o 20::1 size ratio for tympanic membrane::oval window enables concentration o Size differential
  o Ossicles together form a level that enables amplification
• In order for this amplification process to work pressure in middle ear must be equal to outside air pressure
  o Have Eustachian tubes to help maintain appropriate pressure

Question 10

Auditory reflex

Answer 10

• If high amp acoustic energy hits your tympanic membrane – and this is then
  concentrated and amplified – wouldn’t this damage your oval window
• You have an acoustic reflex in place to prevent this
• Tensor tympani muscle on tympanic membrane and stapedius muscle on stapes
  o When high amp acoustic energy arrives, these muscles contract and resist the movement of the tympanic membrane and ossicles
  o Dampen noise by ~30dB - 2 pitfalls of the reflex
  o Primarily works for low-frequency sounds
   Sensitive to only low end – if you have high amp sound wave this
  doesn’t work as well and can damage hearing
  o Takes 50ms to initiate
   There is a delay before the muscles tense
• So high amp, abrupt stimuli can damage the middle and inner ear o Not common in nature
  o Guns and cars and missiles are higher frequency
• If acoustic energy hit your oval window with no tympanic membrane
  o If you damage tympanic membrane – break it mechanically, or pop it due to unequalised pressure, or infection
  o Reduces hearing capabilities – won’t have amplification process o Reduced by ~30dB
  o Normal conversation sounds like a whisper
  o Is able to fix itself unless repetitively damaged

Question 11

the Inner ear

Answer 11

Cochlea has 3 compartments
o Scala vestibuli
 Top bit – where stapes hits into oval
window
o Scala tympani
 Bottom bit
o Midline compartment
 Where sensory neurons (hair cells) are
 Has connection to tectoral membrane
and CNVII

Question 12

The Inner ear (Inner hair cells)

Answer 12

o Close to the inside of the compartment
o Majority of signal transduction – when they bend, release glutamate to the
next cell (auditory nerve fibre) into CNVIII
o Have heaps of afferent fibres going to the brain
o If you make a mouse that lacks functioning in IHC = deafness

Question 13

The Inner ear (Outer hair cells)

Answer 13

o Further away from inside of compartment
o Help to amplify the cilia bend so that signal transduction can occur o Cilia have direct connections to tectorial membrane
 Facilitates movement of membrane
o Can purposefully bend OHC and move membrane more by having efferent
connections – from the brain
 Mostly from superior olive – tells OHC to bend more or less
 Functionally important for high sensitivity hearing
 In a quiet room – send efferents to help hear better
o Help generate pain signal from the inner ear
 Mouse without IHC still exhibits nocifensive behaviour to high dB
noises via OHC pathway
 Still responds to loud noises in a pain type behaviour

Question 14

Other ways to initiate vibration in cochlear fluid

Answer 14

o Can move fluid by moving – spinning around o Vibrate bone
 Get acoustic energy from pressure change from mouth while you talk
 Vibrate the bone which moves the fluid
 Use this to test hearing loss
 Your voice sounds different to you
 We get two different sources of acoustic energy that gives the perception of our voices

Question 15

Auditory pathway

Answer 15

• Cochlea-auditory nerve- cochlear nucleus in medulla- superior olivary
  nucleus in medulla-inferior colliculus in midbrain - MGN of thalamus - A1
• From the cochlear of both your ears into cranial nerve VIII
• Synapse into the medulla at the cochlear nucleus
• Medulla synapses to another nucleus – inferior colliculus in midbrain
  o Also sends projections across to another nucleus in the medulla – superior olive
   Then to midbrain
• Ascending up to the thalamus and to auditory cortex

Question 16

Localisation (Auditory Pathway)

Answer 16

o Pathway decussates but also sends info up the same side
o Info to cochlear nucleus – from goes across and some ascends up the same side after it goes to the superior olive
o Get spatial integration of sounds coming from the left and right
o Gives you localisation – integrate information from the two ears
o This is why we have the circuitous route going through the superior olive
 Why info is sent up both sides
 Gives spatial localisation
 Integrate info from two ears which gives spatial resolution – where the
acoustic energy is coming from

Question 17

Binaural neurons (Auditory Pathway)

Answer 17

o Within the superior olive
o Receive information from both sides of the CN coming in – from both ears
o Compute the interaural time difference and interaural intensity difference
between ears
 Which side did the acoustic energy enter first
 Is it higher amp on one side or the other
 Together helps to optimise sound localisation L/R
 Where stuff is happening in the environment
 High intensity spatial information

Question 18

Primary auditory cortex A1 (Cortical processing)

Answer 18

o Tonotopically organised – areas segregated by tone
 Overrepresentation of Hz frequencies that are low-mid ranges
 Hear a lot of speech so deveop more space devoted to processing that information
 This is the range that predominates human speech o Concentric, hierarchical processing

Question 19

Central Core Area (Cortical processing)

Answer 19

o Primary auditory region (A1)
 Responds to specific frequencies, simple tones – basic info
 Has minimal adaptation
 Always fires when acoustic stimuli are present
 Don’t adapt to it when the sound continues – try to ignore but will still hear it

Question 20

Surrounding Areas (Cortical Processing)

Answer 20

o Secondary auditory regions (belts)
 More complex info
o Tertiary/association regions (parabelts)
 Even more complex info
o Features of both
 Respond to complex sounds, sort features of sound
 Both exhibit adaptation
 When enviro is more cluttered and mixed – can adapt a bit better to
that and stop hearing

Question 21

Hierarchy of processing info (Cortical processing)

Answer 21

o Starts basic and adds on information as your move from A1 out into the belts and parabelts

Question 22

Three basic levels of auditory processing

Answer 22

1. Spatial localisation
   o Where did it come from – survival aspect – useful in alerting you o The posterior/dorsal belt area provides ‘where’ info
    Spatial info – where sound is coming from
    If damaged – can hear a person calling you but won’t know what
   direction it came from
   o Binaural integration
2. Sound recognition
   o Which sound belongs to which thing
    Can parse out based on recognition ranges
   o The anterior/ventral belt area provides ‘what’ info – recognising different sources of sounds
    Patterns of voices vs drinks clatter
    If damaged – can hear something yelling from behind but won’t
   recognise the voice, or perhaps even recognise it as a voice
   o Sorting different sources of sound via:
    Localisation, common spectral content and time course, familiarity
    Optimise that signal vs everything else
3. Signal to noise optimisation
   o Usually try to listen to a signal of interest and declutter background noise – something you want to pay attention to and other signals you don’t
   o Also anterior/ventral belt
   o Overcome amplitude/frequency masking
    If everything is the same amp – hard to pick out signal from noise
    Make signal larger amp to overcome masking effect – talk louder
    If someone is talking at similar frequency to background – even
   increasing amp, it can still be hard to hear them
   o Additional level of binaural unmasking

Question 23

The 3 levels of process allow:

Answer 23

o Parsing – separate out which noises belong to which thing
 Attend to distinct sounds within a scene
 Separate into different streams of info
o Binding – identify that all the sounds together belong to a party for e.g.
 Generate a unified auditory scene
 Info from all direction at all times but able to make a unified
experience
o Also allow you to function in audibly cluttered environments and detect
important sounds

Question 24

Loudness (encoding)

Answer 24

o Larger amp sound waves cause larger displacements in the basilar membrane  more hair cells bend  more neural potentials generated
o The more neural activity (population activity) sent up the auditory relay, the higher the intensity/loudness of the percept
o Loudness is frequency encoded (rate encoded)
 Higher firing rate encodes louder sounds – how many action potential correlates with how loud or soft the sound is
 Larger amp = louder noise

Question 25

Pitch (encoding) | Temporal theory

Answer 25

 Basilar membrane vibrate at a frequency that matches the frequency of the sound wave  50 Hz sound wave causes a 50 Hz vibration in the stapes  This transferred to the cochlear fluid, producing a 50Hz oscillation in fluid  Hair cells bend at 50Hz interval  Afferent fibre APs are phase locked to 50Hz o Sometimes neurons can't fire that fast, especially at frequency gets higher – need to have rests between o Fibres fire at the crests at sound wave – miss some o Maybe another fibre nearby fires at the missed ones  Across the population of fibres/neurons, a 50Hz signal is generated and propagated upstream  Perception of 50Hz pitch results  2 shortcomings  Neurons can't fire in excess of 1000 Hz o Yet the human range of pitch perception ranges 20 to 20,000 Hz o Even if there are multiple neurons firing together the range will only be about 3000 Hz  Basilar membrane doesn’t vibrate uniformly o Differs in width and flexibility o Some parts are stiff and might move every second one o Tips might vibrate at 50Hz but not all of it

Question 26

Pitch (encoding) | Place theory

Answer 26

 Different regions of basilar membrane vibrate in response to different frequencies of sound wave  Georg von Bekesy studied post-mortem cochleas and discovered that basilar membrane is:  Not uniform in shape through cochlea o Shape and thickness varies o Starts thin and gets wider – is not going to move at same speed through cochlea  Tonotopically organised – different areas of membrane respond maximally to different frequency soundwaves o Different frequency ending in the membrane at different points o 100 Hz is deflected earlier on compared to 25 Hz  Shortcomings  At low frequency <50Hz there is a universal deformation  At lower frequency temporal theory kicks in

Question 27

Auditory fibres

Answer 27

- Each region of basilar membrane responds maximally to a specific frequency of soundwave - Thus auditory fibres connected to that portion of membrane will response maximally to a specific frequency of soundwave - Each fibre exhibits a characteristic frequency o The hair of the hair cell has a frequency so the corresponding fibre has a specific frequency it responds to - There is a range for the fibre where it will respond even when dB are low o When out of the range you need massive dB to have it respond o All across membrane there are all sort of fibres responding to different frequencies

Question 28

Each auditory fibre exhibit a unique intensity threshold

Answer 28

o Recording from a population of hair cells – all have a characteristic frequency ~900 Hz but intensity thresholds differ  Fibre 1 = 2dB  Fibre 2 = 10dB  Fibre 3 = 20dB  Fibre 4 = 80dB o At 80dB all four of them fire because all of their thresholds for firing are met o They recognise a specific frequency and within that population of frequency specific cells there are amplitude specific cells  Allow to distinguish volume o If you only have place theory you wouldn’t be able to distinguish volume differences within a pitch - The combo of characteristic frequency and intensity threshold is important o It enables you to distinguish loudness within a pitch

Question 29

Encoding

Answer 29

- The submodality of pitch is mostly spatially encoded (place theory) o Exception: very low frequencies (<50Hz) are temporally encoded (temporal theory) - The submodality of loudness is encoded by the level of population activity sent through the auditory system o Rate encoding/frequency encoding

Question 30

Testing hearing

Answer 30

- Threshold tests o Detection – can you hear that o Method of constant stimuli o Method of limits o Method of adjustment - Improves objective threshold tests o Forced-choice test o Signal detection test o These give confidence – make sure they are actually hearing - Quantification o Quantifying perception of loudness and pitch is not always easy

Question 31

Psychophysics of audition

Answer 31

o Controlled, reproducible auditory stimuli of known amplitude and frequency easy to produce o Experimental confound  For threshold detection, pitch and loudness are interlinked in terms of psychophysics o Ramifications of this confound  To do an accurate psychophysical assessment for hearing, your stimuli needs to span a large range of frequencies and amplitudes  Different dB stimuli in variety of frequencies  Map out audibility function – map where things become audible, what is detectable  Anything below the line is inaudible  Compare the dip to standard curves to determine if they have hearing loss  Once you get to 1000Hz stimulus only has to be low dB  This is why some stereos have a bass boost or loudness button to amplify low frequency so you can hear low frequency at low volume  Take the low frequency signals and boost the dB to let you perceive them o Participant variables  Identification of pitch is highly variable between individuals  Familiarity and practice with certain pitches will influence A1 tonotopic map  Tonal language fluency, musical training  Perception of loudness and pitch decreases with age

Question 32

Hearing Loss

Answer 32

- The most common sensory disability - Deafness = no detection under 82 dB o Profoundly deaf is no detection at all o Still tactile detection if loud enough - Impairment = any loss in audition relative to normal young adult - Can be isolating, frustrating, scary o Isolated from others and void of a background din - On the curve o Has to be 80dB or above to hear 1000Hz and up o Maybe a person with hearing loss or elderly

Question 33

Four types of hearing loss

Answer 33

1. Conduction loss o Impairment in outer/middle ear’s ability to transmit/amplify sound o = reduced sensitivity to all frequencies o Could be due to ear wax, infection, tympanic membrane perforation/rupture, Eustachian dysfunction, otosclerosis of ossicles (lose ability to move over time) o If can't transmit signal to cochlea all frequency will be affected 2. Sensorineural loss o Impairment in inner ear signal transduction and transmission o = reduced sensitivity to specific frequencies or total loss if no functioning hair cells o Use bone conduction to determine if hearing loss is up-stream or down- stream of the cochlea  If can hear is on bone conduction then cochlea is working 3. Age related hearing loss o = presbycusis (old, hearing) o Men lose more auditory capabilities than women o At15,<20kHz o At30,<15kHz o At50<12kHz o Low dB ad higher frequency loss o Possible reasons  Loss of cochlea elasticity?  Loss of nutrients to maintain cochlear health?  Cumulative exposure to loud noise throughout industrialised life – socio reasons  A 70 year old African elder has normal young adult hearing  Damage to auditory system progressively – just part of the society you live in 4. Noise exposure o = socioacusis o Loud, abrupt noises can damage auditory system o Sustained, long term loud noise can damage also o Day to day social life stuff – cumulative loud day stuff o Music: loud earphones, concerts, clubs, musicians o Occupational: factories, blenders, hair dryers, lawn mowers o Transport: cars, trains, motorcycles o Crowds: bars, sporting events, lecture halls

Question 34

Compensating for hearing loss

Answer 34

- Amplify the acoustic energy via a hearing aid - Implant a prosthetic ossicles - Cochlear implant o Implications for plasticity  If auditory cortex is set up a certain way and all of a sudden send signals the brain has never had before – can it cope? o Psychosocial implications  Parents part of deaf community  Want child to be part of community  With an implant – won't be deaf but won't be able to hear perfectly either - Regenerate damages/dead/missing hair cells? o Stem cells? o Can't fix hair cells – don’t grow back

Question 35

Functions of audition

Answer 35

- Identify, localise and react to things in the environment - Communicate o Non-speech vocalisation – screaming, crying o Speech vocalisation o Noisemakers – fire alarm has meaning o Music – emotion in a song, or the words - Audition is key for receiving and producing communication o We hear and simultaneously process the sound of our own voice o If listening to incongruent audio input of distorted speech sounds, we alter our articulations to try and correct o Make adjustments while you speak – constant sensorimotor feedback

Question 36

Week 7 Audition