Hearing

Question 1

What are the functions of the pinna and auditory canal making up the outer ear?

Answer 1

PINNA - Determination of sound location

CANAL - Length + wax = protection of eardrum, helps keep outer and middle ear at constant temp

Question 2

What is meant by RESONANCE in the auditory canal?

Answer 2

Sound waves reflected back from the eardrum interact with new sound waves arriving and this reinforces sound frequencies
RESONANT FREQUENCY - The frequency reinforced the most, determined by the length of the canal (Longer = lower RF = lower pitch)

Question 3

What are the ossicles of the middle ear?

Answer 3

Malleus
Incus
Stapes - vibration passes to OVAL WINDOW and then to liquid in cochlea (inner ear)

Question 4

Why are the ossicles so important?

Answer 4

If vibrations simply through air, <1% of vibrations would reach inner ear - ossicles concentrate the vibration onto the oval window i.e. smaller area, arranged to create an effective lever action

Question 5

Why are the middle ear muscles so important?

Answer 5

Attached to the ossicles to dampen their vibration by contracting at high sound intensities –> protects the inner ear against painful/damaging stimuli

Question 6

What happens when ossicles are damaged?

Answer 6

If beyond surgical repair, sound needs to be increased 10-50x to achieve same level of hearing

Question 7

What is the structure and function of the inner ear?

Answer 7

Semicircular canals and cochlea
Transduce stimulus from pressure changes into electrical signals, and then processes those signals to indicate sound qualities

Question 8

What are the key structural components of the cochlea?

Answer 8

Tympanic and vestibular ducts (vestibular is more superior)

Organ of corti and basilar membrane (cochlear partition)

Question 9

What are the key structural features of the Organ of Corti?

Answer 9

Tectorial membrane - Extends over the hair cells
Inner hair cells- ~3500 cells and cilia on them bend when the organ of corti and tectorial membrane move because they are in contact with the liquid in the cochlear duct
Outer hair cells - ~12000 cells and cilia on them bend from tectorial membrane,
Auditory nerve fibres - feed from the hair cells and become the cochlea branch of CN8
Basilar membrane - up and down movement due to vibrations travelling through from the oval window

Question 10

What is meant by “frequency coding”?

Answer 10

Can have place coding or temporal coding to figure out what the frequency of a tone is
PLACE = which fibres are firing in the cochlea, and this is effective across the whole hearing range
TEMPORAL = timing of auditory nerve impulses in auditory nerve, effective up to 4000Hz which is the frequency at which phase locking stops

Question 11

What is meant by PHASE LOCKING?

Answer 11

Phase Locking is an empirical observation that supports the volley principle. When auditory nerve neurons fire action potentials, they tend to respond at times corresponding to a peak in the sound pressure waveform, i.e., when the basilar membrane moves up.

Question 12

What is the chemical significance of the cilia on the hair cells?

Answer 12

When they bend one way under the tectorial membrane, the movement opens up membrane channels in the cells and ions flow in –> creation of electrical signals and release of neurotransmitter from hair cell
When the cilia move back, the ion channels close and signals stop being generated

Question 13

Distinguish between inner and outer hair cells

Answer 13

INNER - afferent input (95% of afferent fibres are from here), detection of sound and transmit it to the brain via auditory nerve
OUTER - efferent input, amplifying role

Question 14

What are sound waves?

Answer 14

Pattern of alternating pressure changes - vibrations move through air molecules but the air molecules themselves do not move
CONDENSATION - Increased density of air molecules leads to local increase in air pressure
RAREFACTION - air molecules spread out to a lower density so decrease air pressure

Question 15

What is meant by “tone chroma”?

Answer 15

All tones have a “height” i.e. the perceptual experience of increasing pitch as frequency gets higher
Notes of the same letter can sound similar at different heights so we say they have the same TONE CHROMA (separation between notes of the same chroma is known as an OCTAVE)

Question 16

What are the properties of sound waves?

Answer 16

Amplitude i.e. difference in pressure between peaks and troughs (loudness, decibels) and frequency i.e. how many times per second the pressure change cycle repeats (pitch, Hz)

Question 17

Why do we use decibels to measure sound amplitude?

Answer 17

Amplitude as a technical measure is not linear, while decibels work on a linear progression so we don’t have to deal with really large numbers

Question 18

What frequency can humans generally hear up to?

Answer 18

20-200Hz (different species have different sensitivities)

Question 19

What is a PURE TONE?

Answer 19

Used in labs but rarely exist in real life - pressure changes occur in a pattern described by a sine wave (sounds in the environment are more complex)

Question 20

What is meant by the tonotopic map?

Answer 20

High frequencies activate the base of the cochlea while low frequencies activate the apex (when one is activated all others are too but less and less as function of distance away)
This map is also found in the primary auditory cortex - neurons that respond best to the higher frequencies are found more posteriorly

Question 21

What happens when there is a lesion in the frontal or dorsal region of the temporal lobe?

Answer 21

FRONTAL - affects the what pathway but can tell where coming from
DORSAL - affects the where pathway but can tell what it is

Question 22

What does Bekesy’s place theory suggest?

Answer 22

Over time, most of the membrane will vibrate but some more than others for a given stimulus
The ENVELOPE represents the maximum displacement caused (determines which cilia move)
Position of peak is function of frequency (tonotopic map)

Question 23

What is meant by COCHLEA AMPLIFICATION?

Answer 23

In live specimens, outer hair cells expand and contract in response to vibration of the basilar membrane - this amplifies and sharpens the membrane movement
Cilia bend one way –> hair cell elongates –> pushes on membrane

Question 24

When is the importance of the amplifying effect demonstrable?

Answer 24

When outer hair cells are destroyed but inner intact –> takes higher intensity stimuli to get fibre to respond esp in frequency range to which fibre initially responded to

Question 25

What are the 2 types of hearing loss?

Answer 25

Conductive - blockage of sound reaching receptors e.g. ear infection or fusion of ossicles
Sensorineural - damage to hair cells, auditory nerve fibres not excited in normal manner e.g. some ototoxic drugs can damage/destroy hair cells

Question 26

What is Presbycusis?

Answer 26

Sensorineural hearing loss where high frequency sensitivity lost
Occurs in ageing and most frequently in men

Question 27

What is noise-induced hearing loss?

Answer 27

Loud noises cause inner hair cells to degenerate (amount of loss varies with exact intensity and duration, and can be temporary or permanent)
Guidelines now recommend workplace noise should never >85db

Question 28

What are cochlear implants and when are they necessary?

Answer 28

Electrodes inserted into cochlea which electrically stimulate cell bodies of auditory nerve fibres along cochlea length utilising the tonotopic map
When hair cells are damaged so hearing aids will be ineffective as there is nothing there to transduce the amplified sound

Question 29

What is a concern with using cochlea implants in children?

Answer 29

If use implants in place of sign language learning, this may handicap their language and subsequent cortical development
Language using sign actually provides a richer experience

Question 30

What is meant by experience-dependent plasticity in relation to hearing?

Answer 30

Training involving a particular frequency increases space devoted to that frequency in the primary auditory cortex, and electrical activity elicited from these areas is stronger i.e. learned modules - neurons shaped to respond better

Question 31

Where does the auditory nerve synapse on its way from the cochlea to the primary auditory cortex?

Answer 31

Cochlear nucleus - each receives info from just one ear, and at crossover point (pons) not all info crosses over, it is more just a communication between the sides
Superior Oliviary Nucleus in the brain stem (auditory localisation)
Inferior colliculus in the midbrain
Medial geniculate nucleus in the thalamus

Question 32

What is meant by BINAURAL and MONAURAL cues for sound localisation?

Answer 32

Bi = temporal differences between the sounds coming to each ear 
Mon = also known as spectral cues, this refers to how the sound reflects off of the head/pinnae depending on sound location

Question 33

What is the “what” pathway?

Answer 33

Starts anteriorly in core and belt and extends to pre-frontal cortex

Question 34

What is the “where” pathway?

Answer 34

Starts in posterior core and belt and extends to parietal cortex and pre-frontal cortex
This pathway involves processing of both auditory and visual input
Responsible for localising sounds

Question 35

What is the difference between auditory space and auditory localisation?

Answer 35

SPACE = technique in which sounds presented over headphones appear to originate from any desired direction in space. The illusion of a virtual sound source outside the listener's head is created. Sound localization cues generate an externalized percept.
LOCALISATION = Locating objects that actually are in different positions based on quality of sound

Question 36

What 3 sound dimensions allow for localisation?

Answer 36

Azimuth (left to right) (from binaural cues)
Elevation (up or down) (from monaural)
Distance

Question 37

What are the 2 types of binaural cues?

Answer 37

Interaural Time difference - if sound more localised to one side it reaches each ear at different times, most effective for low-freq
Interaural Level difference - difference in pressure level arriving due to the head creating a barrier that reduces intensity reaching far ear, occurs most for high-freq sounds (Acoustic shadow)
Both =localisation along azimuth axis

Question 38

What are spectral cues?

Answer 38

Information for localisation is contained in differences in the spectrum of frequencies reaching our ears from different directions, which are reflected by pinnae and head before entering canal
Paul Hofman found that if pinnae are smoothed out, vertical localisation (esp for high freq) is harder

Question 39

What is the “cone of confusion”?

Answer 39

A cone-shaped set of points, radiating outwards from a location midway between an organism’s ears, from which a sound source produces identical phase delays and transient disparities, making the use of such binaural cues useless for sound localization.

Question 40

What did Hofman’s experiments demonstrate?

Answer 40

Development of associations of new spectral cues when molds fitted, and localisation remained excellent after molds removed suggesting old cues still present also - so different neuronal sets involved, new correlations between spectral cues and location

Question 41

What is meant by “narrowly tuned” neurons?

Answer 41

Neurons that respond best to a particular ITD (found in the superior oliviary nucleus and inferior colliculus)

Question 42

What does the Jeffress model suggest?

Answer 42

Neurons as COINCIDENCE DETECTORS - only activate where spatial summation from both left and right ear inputs
If stimulus straight ahead, middle neuron (e.g. third out of 5) will be the point at which both inputs arrive simultaneously
If a stimulus is from the side, simultaneous activation will reach a different neuron
These neurons are therefore identifying the ITD

Question 43

What are “broadly tuned” neurons?

Answer 43

Experiments have suggested that neurons in the right hemisphere respond best to sounds from life and VV, and localisation is indicated by the ratio of response of these two types of broadly tuned neurons

Question 44

What is meant by the “auditory scene”?

Answer 44

Vast array of environmental sound sources which need to be separated out into separate perceptions for identification - we have to decide which frequency components belong together to form each sound

Use localisation to help in natural settings, but with recordings we cant

Question 45

What 6 principles aid the process of “auditory grouping”?

Answer 45

1) Onset time
2) Location (if a sound is continuous while changing location we perceive one sound e.g. car moving)
3) Similarity of timbre and pitch (scale illusion)
4) Proximity in time (if too far apart, similarity by pitch will not even be recognisable)
5) Auditory continuity (perceived as continuous)
6) Experience - melody schema

Question 46

What is the Precedence Effect when hearing inside rooms?

Answer 46

If a delay between lead and lag sounds is longer, they are perceived as separate, but shorter delay means the sound is perceived as coming from only the lead source (i.e. source that arrives first)

Question 47

What are “indirect” sounds?

Answer 47

Sound reflected off of walls - lower db level than direct sound, and delay reaching ears is relative to room size
Affected by architectural acoustics - amount absorbed/reflected, shape and size of room
REVERBERATION TIME is the amount and duration of indirect sound in a room (time to reduce to 60db, which should be 2sec to avoid echoes)

Question 48

How can hearing and vision influence each other?

Answer 48

Vision affects hearing - ventriloquism effect, sound left to right will appear right to left if watching something move right to left
Hearing affects vision - see something as a collision if hear sound as two objects become adjacent

Question 49

What is meant by “fundamental frequency” of a complex tone?

Answer 49

It’s repetition rate

Question 50

What is “additive synthesis”?

Answer 50

Complex tones consist of pure tones
A complex tone can be built by adding pure tones using as the “first harmonic” a pure tone of the required fundamental frequency
Each subsequent tone added should be a multiple of this frequency - these are “harmonics”

Question 51

What is “periodicity pitch”?

Answer 51

We perceive pitch of a complex tone the same even when the first harmonic is removed - pitch determined by harmonic spacing which indicate the fundamental frequency whether it remains present or not

Question 52

What does sound loudness depend on?

Answer 52

Both sound pressure and frequency - 100Hz at 40db is quiet but 1000Hz at 40-db is loud, so we need to know both features to know loudness

Question 53

What are “equal loudness curves”?

Answer 53

Indication of number of decibels needed to create the same perception of sound loudness at different frequencies

Question 54

What happens during “auditory masking”?

Answer 54

The threshold for frequencies closest to the masking tone are raised most, and the masking effect spreads more to higher frequencies than low ones i.e. basilar membrane vibration caused by masking tone overlaps higher freq vibration more

Question 55

What does the timbre of a sound depend on?

Answer 55

Harmonic tone structure, and time course of the tone i.e. attack and decay

Question 56

What is the difference between Wernicke’s and Broca’s aphasia?

Answer 56

Wernicke - area in superior temporal gyrus involved in language comprehension - can speak fluently but words make no sense
Broca - Can understand but have impaired speech fluency

Question 57

What is cortical deafness and why is it rare?

Answer 57

Patients struggle to recognise both verbal and non-verbal auditory stimuli
Requires bilateral damage to auditory cortex

Question 58

What is the difference between hearing loss and deafness?

Answer 58

Hearing loss = decreased sensitivity to sound, moderate to severe
Deafness = loss of hearing so profound that even speech not perceived, even when hearing aids

Question 59

What clinical evidence supports the existence of WHAT and WHERE pathways?

Answer 59

Temporal lobe damage - can locate sound but can’t identify
Parietal and frontal damage - identify not locate
Brain scans - processing pitch shows activation more in ventral regions e.g. anterior temporal, while sound localisation more in dorsal regions (parietal and frontal)