hearing

Question 1

what is a sound?

Answer 1

• alternating waveform consisting of compression and rarefaction and separating of air molecules
• an oscillating object will cause air to become more or less dense

Question 2

what equation works out wavelength

Answer 2

• distance between each troph
• velocity/frequency

Question 3

frequency (pitch)

Answer 3

• hear because your brain can dissociate between different frequencies
• if not it would be a continuous noise

Question 4

define amplitude (decibels)

Answer 4

• generally expressed as a ratio
• intensity in decibels = intensity unknown sound/intensity of standard x 10log10
• standard is mean hearing threshold
• standard mean corresponds to 10 to power of -11 movement in air molecules

Question 5

what is the range of human hearing

Answer 5

• frequency = 20-20000Hz
• Amplitude = 0-140dB

Question 6

do we have lower sensitivity to low frequencies?

Answer 6

• yes
• sound pressure levels adjusted to A weighting
• down-scales low frequencies to acknowledge lower sensitivity

Question 7

presbycusis

Answer 7

• as you get older you lose auditory hair cells
• influences high frequencies
• 20 y/o have lower vol of sound to perceive it than older

Question 8

having ability to listen to ten octaves of hearing

Answer 8

• first 2 octaves = low bass 20-80Hz
• Third and forth = upper bass 80-320Hz
• fifth-seventh = mid-range 320-2560Hz
• eighth = upper mid-range 2560-5120Hz
• ninth-tenth = treble 5120 to 20,000Hz

Question 9

neurons in the ear and its frequencies

Answer 9

• primary afferent neurons coming from cochlea - sends auditory info to brain
• you can define frequency responsiveness of any neuron in terms of a tuning curve
• neurone responds preferentially to a frequency
• neurons respond differently to different frequencies

Question 10

what is the basic anatomy of the ear

Answer 10

• three parts
• outer = air filled, tympanic membrane (eardrum)
• middle = air filled, ossicles
• inner = fluid filled, cochlea and vestibular system

Question 11

how sound moves through ear

Answer 11

1. tympanic membrane deflects
2. middle ear bones moves and pushes oval window
3. membrane in oval window moves causes cochlea fluid to move back and forth
4. basilar membrane moves (contains organ of hearing)

Question 12

roles of the ossicles

Answer 12

• middle ear acts as a lever
• ossicle bones = malleus, incus and stapes
• convert high amplitude/ low force motion at eardrum into low amplitude/high force motion at oval window
• called impedance matching

Question 13

what is the stapedius reflex

Answer 13

• 2 muscles act on ossicles
• contraction of muscles pulls stapes away from oval window
• decreases transmission of vibrational energy to cochlea
• stapedius reflex occurs in response to very loud sound
• occur during speech
• prevents hearing damage

Question 14

what happens when sound gets to cochlea

Answer 14

• sound vibrated through ears
• outer chamber of fluid vibrating
• 3 chambers (scale) vestibule, media, tympani
• when sound comes in it shifts column of fluid back and forth

Question 15

basilar membrane

Answer 15

• organ of corti within it
• auditory nerve comes out of it

Question 16

organ of corti in detail

Answer 16

• does the work
• 2 rows of hair cells inner and outer
• vestibular hair cells = physical motion
• auditory hair cells = physical motion poured by sound
• embedded in tectorial membrane
• underneath is the basilar membrane

Question 17

what happens in organ of corti when sound reaches it?

Answer 17

• vibration of basilar membrane
• cause relative motion of tectorial membrane = activates hair cells

Question 18

what type of hair cells do we have?

Answer 18

• one cell = kinocilium
• rest of the hair cells = stereocilia
• moving towards little hairs you get inhibition
• move towards kinocilium you get activation

Question 19

what is pitch place theory?

Answer 19

• when basilar membrane wobbles, different parts of it will be activated at different frequencies
• closer to oval window = high frequencies
• other end = low frequencies

Question 20

high frequency sound activates basilar membrane where?

Answer 20

proximal end

Question 21

what is Fourier analysis

Answer 21

• the ear is one
• any waveform can be decomposed into sine waves of various frequencies

Question 22

explain tuning of hearing

Answer 22

• far more sharp by the passive mechanics of basilar membrane alone
• amplification happening

Question 23

amplification happening

Answer 23

• inner hair cells for sensation
• outer are for amplification
• outer contain prestin so whole cell can oscillate
• they will exaggerate sound through positive feedback cycle (active undamping)

Question 24

can outer hair cells generate sound

Answer 24

• yes
• otoacoustic emissions are echos in response to clicks delivered to ear
• ## absense indicates problem of inner ear

Question 25

what is hearing most sensitive for?

Answer 25

- speech - 400-3000Hz

Question 26

temporary notch

Answer 26

- damage depends on level and duration - anything over 85dB is potentially damaging - mild notch at 4kHz

Question 27

what happens to sound once its past as primary afference

Answer 27

- sound activates many areas from cochlear to auditory cortex - arrives in brainstem via 3 neurons - passes through colliculus and arrives at primary auditory cortex

Question 28

what is the primary auditory cortex

Answer 28

- responsible for your perception of sound

Question 29

what is the superior olive

Answer 29

- in brainstem - decifers differences in loudness and timing

Question 30

what is sound localisation?

Answer 30

- distance (range) and bearing (azimuth and elevation) - judge distance = high frequencies travel less well (far away is dominated by bass) - bass travels best, sibilants worst (relative attentuation) - echoes - reverberation - judging direction = inter-aural timing/phase differences with left and right ear - inter-aural volume differences - spectral colouring - loss of high frequencies through head

Question 31

what is the cocktail party effect?

Answer 31

- to understand conversation from an individual speaking amongst many others - involves localisation cues and vision

Question 32

what are inter-aural volume differences?

Answer 32

- ILD - head provides sound shadow - better for high frequencies (whistle nerve right ear it is much louder in right) - bass sounds volume in both ears similar - vowels emphasised, sibilants attenuated more far away and speech becomes more bass

Question 33

inter-aural time delay

Answer 33

-ITD - click from left will arrive at left ear first then right soon after - detect ITDs at 10us (1degree)

Question 34

explain the Jeffress theory

Answer 34

- ITD detection - involved superior olive - neurones in this act as coincidence detectors - neuron splits into 5 different pathways when reaching olive (5 left 5 right) - action potentials arrive simultaneously from both ears, MSO neurone more likely to fire - relies on differing lengths of axons and provides a neuronal map of sound location

Question 35

inter-aural phase differences

Answer 35

- better in low frequencies - if sound is a continuous tone, use phase difference to localise - not useful when wavelength is shorter than head (high frequency) - L-R difference of 360 degree sounds same as 0 degree

Question 36

does your head size matter?

Answer 36

- big heads = large L/R time difference - use timing differences (ITD) - small heads = not much L/R time difference - loudness differences (ILD_ - small heads = better detecting high frequency

Question 37

what is the cone of confusion?

Answer 37

- sounds emanating from different locations can produce identical ILD and ITD profiles at two ears - e.g., sounds from behind can sound like the front - if you tilt or turn head it alters the cone so a previously ambiguous sound is now localised

Question 38

what does the pinna of your ear do?

Answer 38

- outer ear - attenuates sounds from certain directions and amplifies from others - invisible to low frequencies (bass) - coming from behind it can shield high frequencies more = different spectral content

Question 39

what sounds are easier to localise

Answer 39

- narrow bands of frequencies and gradual onsets and offsets are harder to localise - longer, more intense broadband sounds attract attention

Question 40

auditory reaction times

Answer 40

- typically 140-160ms - visual reaction time is slower at 180-200ms - frequency matters - 1kHz = optimal reaction

Question 41

startle responses

Answer 41

- loud sound 120dB - evokes blink at 40ms and neck contraction at 80ms - mediated by brainstem - bypasses cortex via reticular formation 80ms

Question 42

can a startle improve simple reaction time

Answer 42

- yes - signal accompanied by loud sound reaction time is faster