Hearing Flashcards
1
Q
what are the principles of sound conduction
A
- an oscillating object will cause air to become more and less dense
- compression and rarefaction
- radiating waves
- wavelength = velocity / frequency
2
Q
how would you define sound amplitude (decibels)
A
- sound amplitude is generally expressed as a ratio
- intensity in decibels = 10log10(intensity of unknown / intensity of standard)
- the ‘standard’ is the mean hearing threshold: 10^-12 Wm^-2
- corresponds to 10^-11m movement of air molecules: less than diameter of hydrogen atom
3
Q
what is the range of hearing
A
- frequency: 20-20000Hz
- amplitude: 0-140dB
4
Q
what is lower sensitivity to low frequencies
A
sometimes sound pressure levels are adjusted using the ‘A weighting’. This effectively down-scales low frequencies to acknowledge out lower sensitivity
5
Q
what are the frequencies of sound
A
- low bass (20-80Hz) includes the first two octaves (bass, tuba)
- upper bass (80-320Hz) includes the third and fourth octaves (cello, trombone)
- midrange (320-2560Hz) includes the fifth through seventh octaves (guitar)
- upper mid range (2560-5120Hz) is the eighth octave
- treble (5120-20000Hz) includes the ninth and tenth octaves
6
Q
what is the role of the ossicles (middle ear)
A
- middle ear acts as a lever
- converts high amplitude / low force motion at ear drum into low amplitude / high force motion at oval window
- impedance matching
7
Q
what is the stapedius reflex
A
- two muscles act on ossicles
- contraction of these muscles pulls strapes away from oval window
- decreases transmission of vibrational energy to cochlea
- stapedius reflex occurs in response to very loud sound
- also occurs during speech
- crucial for preventing hearing damage
8
Q
what is the make up of the cochlea (inner ear)
A
- 3 scalae
- vestibuli
- media
- tympani
- helicotrema
- round window
9
Q
what is the organ of corti
A
- outer hair cells motois (prestin)
- inner hair cells sensation
- tectorial membrane
- basilar membrane
- small up-down movements of the basilar membrane cause a large relative shear of the tectorial membrane, thus activating the hair cells
10
Q
what is fourier analyser
A
- any waveform can be decompressed into sine waves of various frequencies
- even a square wave can be made up of sine waves
- combine the fundamental frequency with progressively smaller harmonics
- decomposes time-based sound signals into their frequency components
11
Q
what is sharpening of the tuning curve
A
tuning of hearing is far more sharp than explained by the passive mechanisms of the basilar membrane alone
12
Q
how can the outer hair cells generate sound
A
- otoacoustic emissions are ‘echoes’ in response to clicks delivered to far
- absence indicates problem of inner ear
- used to asses hearing in newborns
- possible mechanisms of some types of timmitus
13
Q
what is the frequency of speech
A
400-3000Hz
14
Q
what causes noise induced hearing loss
A
- concerts can cause temporary loss notches
- damage depends on level and duration
- anything over 85dB is potentially damaging
15
Q
what is the auditory pathway to the brain
A
- sound activates many areas from cochlear nerve to auditory cortex
- sound related brain activation measured using EEG
- Broca’s speech area - ‘expressive’
- Wernicke’s speech area - ‘receptive’
16
Q
what is sound localisation
A
distance (range) and bearing (azimuth and elevation)
17
Q
what is the ‘cocktail party’ effect
A
- we can understand conversation from an individual speaking among many others
- involves sound localisation cues (as well as vision)
- judging distance
- high frequencies travel less well; far away sounds dominated by bass
- expectation (e.g. intensity of voice)
- relative attenuation (timbre)(bass travels best, sibilants worst)
- echoes (multiple echoes - reverberation - less attenuation)
- judging direction
- inter-aural timing / phase differences
- inter-aural volume differences
- spectral colouring (by head and pinna)
18
Q
how does inter-aural volume differ
A
- the head provides a sound ‘shadow’
- attenuates volume in ear opposite sound source
- greater attenuation for high frequency sounds
- hence, far away speech more bassy (vowels emphasised, sibilants attenuated)
- better for high frequencies
19
Q
how does inter-aural timing differ
A
- better for low frequencies
- inter aural time delay (ITD): a click from the left will arrive at the left ear first, then right ear soon after
20
Q
what is Jeffress theory of ITD detection
A
- neurons in superior olive (brainstem) act as coincidence detectors
- when action potentials arrive simultaneously from both ears, MSO neuron more likely to fire
- relies on differing lengths of axons
- provides a neuronal map of sound location
21
Q
how does inter-aural phase differ
A
- if sound is a continuous tone, use phase difference to localise
- not very useful when wavelength is shorter than the head (i.e. high frequency sound)
- L-R difference of 360 degree sounds the same as 0 degree ambiguous
22
Q
does head size impact hearing
A
- big head = large L/R time difference
- small head = not much L/R time difference
- however, smaller heads better for detecting high frequency sounds
23
Q
what is the cone of confusion
A
- sounds emanating from different locations can produce identical ILD and ITD profiles at the two ears
- e.g. sounds emanating from behind can sometimes sound in front of the head
- tilting and turning the head alters the cone of confusion
24
Q
what is spectral colouring by pinna and head
A
- the outer ear (pinna) attenuates sounds from certain directions, amplifies sound from others
- invisible to low frequency sounds
- therefore, the spectral content of sound combined with prior experience, can be used for localisation
25
what is binaural reading
- high fidelity recording studios often use binaural microphones
- mimics interaural difference in humans
- produces a more pleasing sound
26
what is the auditory reaction time
- typically 140-160ms
- visual reaction time slower (180-200ms)
- sound takes about 3ms per metre
27
what are startle responses
- evoked by loud sound ~120dB
- evokes blink at ~40ms
- neck contraction at ~80ms
- too fast to involve cerebral cortex
- mediated by brainstem
28
how can startle responses improve reaction time
- when signal is accompanied by loud sound (120dB) reaction time is much faster (from ~170 to 80ms in extreme case)
- <100ms reaction time considered false start in olympics
