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Control of Human Movement > Hearing > Flashcards

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
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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
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3
Q

what is the range of hearing

A
  • frequency: 20-20000Hz
  • amplitude: 0-140dB
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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

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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
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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
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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
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8
Q

what is the make up of the cochlea (inner ear)

A
  • 3 scalae
    • vestibuli
    • media
    • tympani
  • helicotrema
  • round window
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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
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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
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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

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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
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13
Q

what is the frequency of speech

A

400-3000Hz

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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
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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’
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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
Q

what is binaural reading

A
  • high fidelity recording studios often use binaural microphones
  • mimics interaural difference in humans
  • produces a more pleasing sound
26
Q

what is the auditory reaction time

A
  • typically 140-160ms
  • visual reaction time slower (180-200ms)
  • sound takes about 3ms per metre
27
Q

what are startle responses

A
  • evoked by loud sound ~120dB
  • evokes blink at ~40ms
  • neck contraction at ~80ms
  • too fast to involve cerebral cortex
  • mediated by brainstem
28
Q

how can startle responses improve reaction time

A
  • 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

Control of Human Movement (21 decks)

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