impaired Hearing Flashcards
Prevalence (UK)
- 1/1000 children at birth (0.1%)
-110/1000 adults aged 61-70 (11
%)
-300/1000 adults aged 71 -80 (30 %)
Pure-tone audiogram
-measures hearing loss
- establishes lowest intensity at which you can detect a pure tone
- Hearing tests starts with teres you can clearly hear + you increase intensity
-establish a pure tone profile
- 0 d B = normal hearing for healthy young adults
- As we age we lose sensitivity to high frequencies
-Hearing loss around 30dB = struggle to hear sounds
Degree of hearing loss
-Pure Tone Average (PTA) is average pine-tone thresholds at 250,500,1000 . 2000 + 4000 Hz
- PTA clinical bands:
-> up to 20dB = normal
-> 21 - 40B = mild impairement ( often not treated)
-> 41 - 70 = moderate impairment ( hearing aids)
-> 71 -95 severe ( hearing aids)
-7 95 + = profound ( cochlear implants)
Prevalence of impaired hearing (world)
- most people fall with moderate category
The more severe the hearing loss the fewer people have it - Rises with age
- proportion of more severe types increases with age
2 main types of hearing loss
- conductive loss
-> loss originates in middle ear
-> roughly equal at all frequencies - sensorineural or cochlear loss
-> loss originates in inner ear
-> greater loss at higher frequencies
conductive loss -causes
-loss of mobility of bones in middle ear
-> Fluid in middle ear (Otitis Media) - typical fer ear infection
-> fixation of the Stapes/ ossicles (otosclerosis)
- affects all frequencies
-Hearing aids/surgery compensate well
- common with babies: antibiotics + insert grommet (pressure-releasing)
Cochlear loss - causes
- most common
_loss/malfunction of cochlear hair cells
-> genetics - mutations Assoc with disappearance/problems with hair calls - > ototoxicity -> toxic effect of drugs lead to hear ell death
-> noise
-> decreased oxygenation -> happens with age as muscles around heart weaken
-often affects high more than low frequencies - Hearing aids compensate partially
what goes wrong when someone has cochlear hearing loss
- Active process in Outer hair cells is impaired
1) Loss of sensitivity
2) Loss of frequency selectivity
3 ) loudness recruitment
4) reduced sensitivity to temporal fine structure
Loss of sensitivity + frequency selectivity
- Healthy cochlea: outer hair cells are active + amplify basilar memb + helps increase sensitivity to low- intensity sounds sharpens
frequency selectivity - impaired coclea - outer hair cells are passive so sensitivity to low-intensity sound decreases + frequency selectivity decreases
Tuning is poorer in ears with cochlear loss
- use people with only 1 ear of impairment to ensure it is just the auditory system impaired
-must detect test tone
-play Masher at same time, adjusting its intensity until listeners can’t hear the test tone
-Normal tuning curve: sharp + masher only effective if has same intensity to test - cochlea loss: market effective at lower intensities , less frequency selective
issues with loudness recruitment
-Hear a tare in 1 ear + select intensity of same tore in other ear
- Listeners with normal hearing are very accurate at matching
- coch year hearing loss match loudness of tone in impaired ear with less intense tone in good ear
- difference decreases with intensity
-Amplity sounds by 50dB
- threshold for discomfort = 100 so sounds les than 50 hurt
Reduced sensitivity. to temporal fire structure- envelope + fine structure
- Temporal envelope = amplitude amplification
-Temporal fine structure = frequency - cochlear hearing loss = difficulty interpreting TFS
-TFS is important for pitch perception - difficulty hearing an indiv when others are speaking at the same time
Moore (2002) -study showing los+ ability of using TFS
-Task = transcribe the female voice
-intensity of males voice is adjusted so they can transcribe 50%
- At neg signal-to-noise ratio , intensity of larger talker , intensity of larger talker is lower than Male
- Listeners with impaired hearing need better signal-to-noise ratio than normal hearing
- impaired hearing benefit less from an increase in TFs
How much can hearing aids help?
-Aim to amplify sound to ear drum
- fitted into ear canal
- Has a microphone, amplifier speaker
- increases intensity of sound so helps with loss of sensitivity
- can’t help with frequency selectivity or Temporal fine structure
- can help loudness recruitment
Profound Hearing Loss
-deterioration of both inner + outer hair cells
-minimal benefit from rearing aids -> only a few words understood + unable to use telephone
- prevalence:
-200 children born a year
-1 adult in 1600
Cochlear implants
- External part resembles hearing aids
-microprocessors convert sound into electrical signal transmitted by coil
-implant attaches to the external part through magnet in Skull
-it bypasses the middle ear - signal processor filters the acoustic signal into 8 + frequency bands
-Temporal envelope is conveyed as an electrical impulse which is transmitted to appropriate frequency specific place
HOW well does a cochlear
implant recreate sound
- Doesn’t provide TFS
- okay for producing speech but isn’t great
- some sounds are well conveyed- dogs barning
- some not conveyed well at all- songs
- some sounds are hard to interpret correctly
outcome of cochlear implant for postlingually deafened adults
-understand 80% of words spoken in quiet
- can use telephone
- much variability
- Best outcome shoun by: deafened recently, retain some residual hearing, have good lang -WM skills + are motivated
Out come for cochlea implantation of prelingually deafened children
- pediatric implantation
-implant before /during Lang acquisition May make huge difference - Hardly differ a lot in first year
- The younger child gets implant, the closer their lang age is to their chronological age
- once a child receives an implant, their expressive lang develops at a normal rate
- The younger child is implanted, the closer their reading age is to their actual age
One ear or two? Bilateral or unilateral?
-potential advantages of bilateral implantation:
> guaranteed implant to better ear
> insurance policy if 1 fails
> potential fer skills in spatial hearing
_potential disadvantages:
> operate on both ears
> cost
implantation policy for NHS
-children born death are eligible to receive 2 implants
-adults who become death =
1 implant
- Blind + death adult = 2 implants
