Final Exam - Readings Flashcards
What are ways in which educating the patient is important?
- provide realistic patient choices
- encourage self-efficacy
- convey sense of unique issues and abilities (one size does not fit all
Prescription procedure
- practical way to select a hearing aid & adjust amplification characteristics for each hearing impaired person
amplification target (prescription target)
required amplification characteristics that can help assume relationship between measured patient characteristics and required amplification characteristics
evaluative approach
- contrast to prescriptive approach
- number of hearing aids or response shapes randomly chosen, each is tested on patient to find the best one
- totally impractical because of the large number of characteristics
Mirroring of the audiogram
the gain needed at each frequency that is equal to the threshold loss at that frequency minus a constant
half-gain rule
- because the original MCL formula didn’t take into account the variation of speech energy across frequency lybarger made a different approach
- averaged across frequencies the amount of gain chosen with approximately half of the threshold loss
- underlies several prescriptive procedures
What are two different auditory things used for the basis of prescription?
MCL
Measuring hearing thresholds
Name reasons why it is hard to determine a relationship between hearing loss and gain.
- depends on type of input signal
- depends on loudness perception and frequency resolution ability
- may depend on nature of the auditory input that a person may be accustomed to
- may not be a single optimum gain frequency curve (because a person may want to have better intelligibility, comfort etc)
REAG
real-ear aided gain
- specifies how much SPL at the eardrum should exceed the SPL in the incoming field
REIG
- real-ear insertion gain
- describes how much more signal should be at the ear drum when the person is aided compared to unaided
REUG
real-ear unaided gain
REAR
real-ear aided response
What are some types of prescriptions for linear amplification?
- POGO
- NAL
- DSL
POGO
- Prescription of gain and output procedure
- straightforward application of the half-gain rule with an additional low cut (low frequency ambient noise)
- insertion gain at each frequency is equal to half the hearing loss at that frequency, plus a constant
- only intended to be used only for hearing losses up to 80 db HL
POGO II
- greater losses, gain increases by 1 dB for every 1 dB increase in hearing loss
- people with severe and profound hearing losses prefer to listen to speech at low sensation level
NAL
- national acoustic laboratories of australia
- maximize speech intelligibility at preferred listening level
- type of gain prescribed by NAL is insertion gain
Why was the NAL formula changed?
- it did not achieve equal loudness, especially for those with a steeply sloping loss
- revised formula became known as NAL-R
NAL-RP
- based on measured speech intelligibility, and subjective preferences for quality and intelligibility in quite and in noise for mild to profound loss
DSL (linear)
- desired sensation level
- wanted to provide audible and comfortable signal in each frequency region
How does DSL differ from POGO and NAL-RP?
- target is in real-ear aided gain instead of real-ear insertion gain
- DSL is convenient for infants and young children
- DSL procedure doesn’t attempt to make speech equally loud but instead comfortably loud
Why is the correct prescription important?
- If you don’t have the ability to change the volume control on your own you can’t compensate for errors made in programing
- they can’t change the frequency response shape, this needs to be done correctly in the programming
What is important to consider when trying to pick between the different prescription methods?
- type and configuration of loss
- hearing aid ability
- age (DSL good for kids and cognitively/dexterity challenged adults)
- technology
Name some difficult issues with prescription.
- dead regions
- prescribing compression thresholds
- need for accuracy and prescription
- preferred loudness
- acclimatization
- adaptation to gain and frequency response
acclimatization
gradual longterm changes in the hearing abilities of patients
adaptation to gain
aspect of acclimatization
- when a patient’s amount of gain preferred may gradually increase over time
- when you first get a hearing aid it seems very loud because your cochlea is used to much less information, as you become more used to the aid you are more willing to hear at louder levels and this helps with speech intelligibility
dead region
when a particular region of the cochlea has no functioning IHC and/or no auditory nerves to which they connect
- this causes range of frequencies in which information will only be received if picked up elsewhere in the cochlea, this information will then be confused
- CAM II prescription is the only one intended to amplify only at frequencies without dead regions
Is it necessary to test for dead regions before prescribing amplification?
not sure - given the potential measurement problems, clinical time involvement and lack of certainty about how to use the results
Where in frequency does speech information exist?
up to 10,000 Hz, the amount of information per 1/3 octave band decreases as frequency increases
What is the problem with amplifying high frequencies for someone with a severely sloping loss?
- you may be able to add enough gain to these frequencies but the information may not be usable
- higher gain makes feedback more likely
Even in the absence of high frequency dead regions, how much high frequency amplification is optimal?
- no simple answer, difficult issue
- several connected issues:
- up to what frequency should speech be made audible
- within this range how should sensation level vary with frequency
- how do the answers to those questions vary with input level and hearing loss
Why is it important to have several channels?
- the greater the number of channels, the narrower in frequency each channel is, and the smaller the within-channel compression threshold will be relative to the overall broadband compression threshold
Name a few general ways that prescriptions differ
- average gain
- response shape
- compression ratio
- compression threshold