hearing Flashcards
1
Q
what is a sound?
A
- alternating waveform consisting of compression and rarefaction and separating of air molecules
- an oscillating object will cause air to become more or less dense
2
Q
what equation works out wavelength
A
- distance between each troph
- velocity/frequency
3
Q
frequency (pitch)
A
- hear because your brain can dissociate between different frequencies
- if not it would be a continuous noise
4
Q
define amplitude (decibels)
A
- 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
5
Q
what is the range of human hearing
A
- frequency = 20-20000Hz
- Amplitude = 0-140dB
6
Q
do we have lower sensitivity to low frequencies?
A
- yes
- sound pressure levels adjusted to A weighting
- down-scales low frequencies to acknowledge lower sensitivity
7
Q
presbycusis
A
- 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
8
Q
having ability to listen to ten octaves of hearing
A
- 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
9
Q
neurons in the ear and its frequencies
A
- 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
10
Q
what is the basic anatomy of the ear
A
- three parts
- outer = air filled, tympanic membrane (eardrum)
- middle = air filled, ossicles
- inner = fluid filled, cochlea and vestibular system
11
Q
how sound moves through ear
A
- tympanic membrane deflects
- middle ear bones moves and pushes oval window
- membrane in oval window moves causes cochlea fluid to move back and forth
- basilar membrane moves (contains organ of hearing)
12
Q
roles of the ossicles
A
- 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
13
Q
what is the stapedius reflex
A
- 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
14
Q
what happens when sound gets to cochlea
A
- 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
15
Q
basilar membrane
A
- organ of corti within it
- auditory nerve comes out of it
16
Q
organ of corti in detail
A
- 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
17
Q
what happens in organ of corti when sound reaches it?
A
- vibration of basilar membrane
- cause relative motion of tectorial membrane = activates hair cells
18
Q
what type of hair cells do we have?
A
- one cell = kinocilium
- rest of the hair cells = stereocilia
- moving towards little hairs you get inhibition
- move towards kinocilium you get activation
19
Q
what is pitch place theory?
A
- when basilar membrane wobbles, different parts of it will be activated at different frequencies
- closer to oval window = high frequencies
- other end = low frequencies
20
Q
high frequency sound activates basilar membrane where?
A
proximal end
21
Q
what is Fourier analysis
A
- the ear is one
- any waveform can be decomposed into sine waves of various frequencies
22
Q
explain tuning of hearing
A
- far more sharp by the passive mechanics of basilar membrane alone
- amplification happening
23
Q
amplification happening
A
- 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)
24
Q
can outer hair cells generate sound
A
- yes
- otoacoustic emissions are echos in response to clicks delivered to ear
- ## absense indicates problem of inner ear
25
Q
what is hearing most sensitive for?
A
- speech
- 400-3000Hz
26
Q
temporary notch
A
- damage depends on level and duration
- anything over 85dB is potentially damaging
- mild notch at 4kHz
27
Q
what happens to sound once its past as primary afference
A
- sound activates many areas from cochlear to auditory cortex
- arrives in brainstem via 3 neurons
- passes through colliculus and arrives at primary auditory cortex
28
Q
what is the primary auditory cortex
A
- responsible for your perception of sound
29
Q
what is the superior olive
A
- in brainstem
- decifers differences in loudness and timing
30
Q
what is sound localisation?
A
- 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
31
Q
what is the cocktail party effect?
A
- to understand conversation from an individual speaking amongst many others
- involves localisation cues and vision
32
Q
what are inter-aural volume differences?
A
- 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
33
Q
inter-aural time delay
A
-ITD
- click from left will arrive at left ear first then right soon after
- detect ITDs at 10us (1degree)
34
Q
explain the Jeffress theory
A
- 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
35
Q
inter-aural phase differences
A
- 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
36
Q
does your head size matter?
A
- 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
37
Q
what is the cone of confusion?
A
- 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
38
Q
what does the pinna of your ear do?
A
- 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
39
Q
what sounds are easier to localise
A
- narrow bands of frequencies and gradual onsets and offsets are harder to localise
- longer, more intense broadband sounds attract attention
40
Q
auditory reaction times
A
- typically 140-160ms
- visual reaction time is slower at 180-200ms
- frequency matters
- 1kHz = optimal reaction
41
Q
startle responses
A
- loud sound 120dB
- evokes blink at 40ms and neck contraction at 80ms
- mediated by brainstem
- bypasses cortex via reticular formation 80ms
42
Q
can a startle improve simple reaction time
A
- yes
- signal accompanied by loud sound reaction time is faster
