MNSR 30 -Hearing Impairment and hearing aids

Question 1

why can’t we use interaural intensity difference for sounds of a frequency < 1kHz

Answer 1

calculate wavelength of sound = wave velocity/frequency
wavelength is large - when it is larger than an obejection
a phenomenom called defraction occurs
no shadow as sound moves around head

Question 2

why do we have 2 ears

Answer 2

localisation occurs via interaural intensity difference

heads casts an acoustic shadow

Question 3

how have animals perfected localisation of sound

Answer 3

barn owl perfected localisation of sound from prey.

ears are at different heights and are asymmetrical allows both lateral and vertical localisation of prey in darkness

Question 4

how are sounds of a frequency less than 1 kHz localised

Answer 4

localised through interaural time difference between sounds travelling different path lengths

Question 5

how is hearing function and hearing loss detected

Answer 5

measured in units of dBHL using an audiometer - produces audiogram
patient wears headphone - audiometer sends a series of tones of fixed frequency and increasing intensity

Question 6

air conduction

Answer 6

detects sounds through the usual auditory route

air propagates through the ear and is detected

Question 7

how can the ear hear sounds other than air conduction

Answer 7

sound is conducted directly into the cochlea through bone in the skull

Question 8

where is the sound in the larynx produced transmitted

Answer 8

transmitted to cochlea via bone conduction

Question 9

why do recordings of our voice sound different

Answer 9

the voice misses the bone conduction portion

Question 10

what is the limitation to testing hearing loss via standard air conduction route

Answer 10

we won’t know where the problem lies

Question 11

where can hearing loss may be caused

Answer 11

problems along the conductive path or in the cochlea

Question 12

how do we test neural hearing

Answer 12

placing small transducers on the bone behind the ear

Question 13

bone conduction

Answer 13

any vibration in the tympanic membrane or ear drum is transmitted to oval window
oval window is in bony structure which is connected to bone part off the skull behind the ear

Question 14

2 types of hearing loss

Answer 14

conductive or neural

Question 15

difference between conductive or neural hearing loss

Answer 15

conductive - physical damage or obstruction in outer or inner ear
neural - permanent damage to nerves in inner ear

Question 16

how is conductive hearing loss detected in audiogram

Answer 16

low hearing level (y axis)

normal bone conduction but impaired air conduction

Question 17

how is neural hearing loss detected in audiogram

Answer 17

high hearing level at low frequency but drop in hearing level at high frequency in both bone and air conduction

Question 18

causes of conductive hearing loss

Answer 18

Ear infection
Earwax
Hole in eardrum
Fluid in middle ear

Question 19

causes of neural hearing loss

Answer 19

Damaged hair cells
Damage to the auditory nerve
Neurodegeneration
noise exposure

Question 20

notch defect

Answer 20

rapid decline in hearing threshold level at a specific frequency range

Question 21

causes of neural loss of high frequency sensitivity

Answer 21

comes with age - presbycusis

Question 22

the dBHL and Hz range between a conversation between people 1 metre apart

Answer 22

60dBHL

100-3000 Hz

Question 23

when are hearing aids required

Answer 23

if audiogram shows more than 55dBHL loss in this frequency

Question 24

why must hearing aids be carefully designed

Answer 24

threshold of pain is usually same for normal hearing

~120dBHL -130dBHL

Question 25

how do hearing aids work

Answer 25

digital electronics enables frequency response of aid to be exactly tailored to individual

Question 26

what is the purpose of the transducer being placed in the bone behind the ear?

Answer 26

vibration is released from transducer and the bone is connected to the bony structure in the ossicles

Question 27

interaural time difference

Answer 27

difference in arrival time of sound between the two ears - used for localisation of sound
for sounds of a frequency <1 kHz

Question 28

interaural intensity difference

Answer 28

difference in sound intensity between right ear and left - for localisation of sound
if sound intensity is greater in right ear than left ear - source must from the right side
for sounds of a frequency > 1.5kHz