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
What is an acceptable gain target measurement
within 5 dB of your target, don’t need to spend more time fine tuning
What is different about non-linear prescriptions
- specify gain-frequency response for several input levels
- average gain and the shape of the frequency response will vary with input level
- prescription can be viewed as specifying an IO curve for several frequencies
Types of non-linear prescriptions
- LGOB
- IHAFF/Contour
- ScalAdapt
- Fig6
- DSL [i/o] and DSLm[i/o]
- NAL-NL1
- NAL-NL2
- CAMREST, CAMEQ, CAMEQ2-HF
LGOB
- loudness growth in half octave bands
- first clinically practical procedure
- patient uses 7 point loudness scale to categorize loudness, the average levels are compared to levels needed to produce the same categories in normal hearing people
- the levels they decide are too loud or not loud enough are decided by triple bursts of half octave bands of noise
IHAFF/Contour
- Independent hearing aid fitting forum
- created based on the need for adjustable wide dynamic range compression
- loudness scaling measure used is called the contour test
- pulsed warble tones ascending in 5 dB increments
ScalAdapt
- combines the three steps within LGOB and IHAFF which are:
- loudness scale measure for the patient
- at each level, the gain needed to normalize loudness is calculated
- the HA is adjusted to match gain target
- clinician adaptively adjusts characteristics of HA until the patient gives desired loudness rating
ex. normal 65 dB SPL says comfortable, then you would adjust until the person with HA says the same
What is a problem with ScalAdapt?
- may not be based on correct rationale
- complete loudness normalization creates excessive upward spread of masking so they make low frequency targets two loudness categories lower than those perceived by normal hearers
FIG6
specifies how much gain is required to normalize loudness at least for medium and high level input signals, not based on individual measures of loudness but rather the loudness data averaged across a large number of people with similar threshold loss so only hearing thresholds are needed for required gain
DSL [i/o] and DSLm[i/o]
- desired sensation level
- i/o compromises two alternative procedures each with its own rationale
- DSLm[i/o] designed to normalize loudness at each frequency except:
- high input levels where limiting prevents loudness discomfort
- low input levels on the grounds that the input is likely not speech
- adults who prefer less gain than predicted by loudness normalization approach
- DSL is used for kids more likely
- m = multi stage, upgrade from DSL [i/o]
NAL-NL1 & NAL-NL2
- maximize speech intelligibility subject to the overall loudness of speech
- first model was developed for effects of HL hearing loss desensitization and the effects of listening at high levels
- second model was a method for calculating loudness again accounting for the effects of SNHL
- only inputs required for these models are hearing thresholds and speech spectrum levels
CAMREST, CAMEQ, CAMEQ2-HF
- similar to NAL, applied in a more sophisticated manner
- total loudness should equal total loudness for normal hearers at the same input level
- reasonable basis for prescriptions for at least mild to moderate hearing losses
- Cambridge Loudness equalization formula
Which of the prescriptions are loudness normalization achieved by loudness scaling?
- LGOB
- IHAFF/Contour
- ScalAdapt
Which of the prescriptions are loudness normalization based on hearing thresholds?
- FIG6
- DSL [i/o] and DSLm[i/o]
- CAMREST
Which of the prescriptions are loudness equalization?
- CAMEQ
- CAM2
Which of the prescriptions have intelligibility maximization?
- NAL NL1
- NAL NL2
Which prescriptions are easier to use in the clinic: loudness judgements or hearing thresholds?
- hearing thresholds
- FIG6, DSLm[i/o], NAL-NL2, CAM2
quarter-gain rule
- for mixed or conductive loss the average gain needed is half of the total loss plus one quarter of the conductive component
When would you use the quarter-gain rule
- when there is a conductive component as well as a SNHL
baseline response
- used to compare program types to when a client is trying to pick best suited programs
real-ear saturated response
equivalent measurement in real ear for the output sound pressure level for 90 dB input level (estimate of max SPL HA can put out)
Why do you find an optimum OSPL90 for a person?
- low enough to avoid discomfort, damage, and wasted output
- high enough to avoid inadequate loudness, distortion and removal of intensity cues to speech
What is the rationale behind setting OSPL90 equal to or just below LDL
OSPL set in this way should not lead to discomfort
- setting OSPL90 as high as possible without causing discomfort should minimize chances of OSPL 90 being too low to cause insufficient loudness or excessive saturation
Two factors affecting wether hearing aid could cause further loss
- person’s susceptibility to noise-induced loss partly depends on how much loss the person already has
- daily noise dose experienced by the aid wearer
Hearing aid management difficulties
- Problems: Inserting, removing, on/off, volume control, changing battery
- Solutions: observe Pts and how they preform different tasks to identify where the difficulty is
teaching Pts how to avoid difficulty inserting EM or ear shell
- Teach landmarks on HA/EM and a specific grip to establish a habit
- If the Helix lock is a problem, you can remove it.
- May also need to remove part of the HA if they cant get the BTE earmold in. for example: taking a skeleton and making it into a semi-skeleton
- If it’s a tight fit, you can apply a lubricant or the shell can be tripped if feedback isn’t likely to result
- Pt may need to pull the pinna up and out with the other hand when inserting
Difficulty locating or using a control
Re-train.;;; If re-training doesn’t work, you can modify or replace it.
Volume control on ITE/ITC can be made more prominent
If theyre confusing buttons/switches you may need to remove one so that the other control (the more important one) can be operated.
• Can increase compression ratio to reduce/eliminate volume control but the sound quality may go down.
Can add remote control
difficulty removing HA
Add a removal handle/line
If Pt can grab but not remove and they cant be trained using a twisting motion, you can remove parts of the EM or shell or you can have a more flexible dome-type ear fitting
difficulty changing battery
Color 1 side of the battery slot to lessen batt. Reversal
Use a tool to open batt. Door
Use magnetic tool to hold batt
Re-fitting w/HA that has a bigger batt compartment (easier to see/open)
Teach Pt to distinguish + side of the battery tactually rather than visually or vice versa (use the removable tab for instructions if that helps!)
Fit a HA with a built in rechargeable battery
ear mold or ear shell discomfort solutions
Ask where it hurts/otoscopy
For CIC discomfort can also be caused by HA too loose or if the Pt pushes it farther than its intended to go.
BTE: incorrectly cut tubing length
Most commonly because the helix lock isn’t tucked in.
Allergic reaction is rare, but possible. Youll need a different material.
Also rare, but sometimes Pts use HAs that were made for the other ear/some elses ear (manufactured prob)
poor EM or ear shell retention solutions
HAs (especially CIC, ITC) can come out of the ear when the jaw moves. Solutions include:
• Remaking HA with a different style (low profile ITE instead of ITC, ITC instead of CIC)
• Make with a longer canal portion or helix lock
• Remake the earmold or shell with a medium viscosity material with Pt jaw open
reasons for voice quality and occlusion problems (hollow, boomy, echoes, in a barrel, like having a cold, plugged)
- The earmold or earshell is excessively blocking the ear canal
- HA is distorting when the Pt speaks
- HA amplifier is excessively amplifying LF sounds
- Pt has forgotten what his/her own voice should sound like (counsel Pt that they just have to get used to it!)
solutions to help with own voice quality and occlusion problems
- Decrease length of vent or increase area.
- Make an earmold/earshell w/a canal stalk long enough to go to the bony part
- –Causes increased difficulty w/insertion and removal and less comfy
- Electronic cancellation of occlusion-generated sounds
reasons why the hearing aid is distorting when the Pt speaks
- The Pts mouth is closer to the input so its louder.
- WDRC compressor provides lower gain to speakers voice. May complain about music quality or naturalness or others’ voices
reasons why the HA amplifier is excessively amplifying LF sounds
- Low freq sounds travel around the head more readily than high freq. high freq sounds are radiating out of mouth instead.
- Solution is decreasing the low-freq gain of the HA for loud sounds and seeing if problem disappears, but this could conflict hearing other sounds
the EM or ear shell is excessively blocking the ear canal
- Blocking the cartilaginous part of the wall can cause vibrations w/in itself
- -For low freq this causes SPL to increase up to 30 dB (normally 15dB).
What problems does feedback cause Pts to report?
- Volume cant get loud enough w/o whistling
- Whistling occurs when they chew, talk, wear hat, put hand/phone near ear
- HA makes a brief noise when certain sounds occur. This is the effect of sub-oscillatory feedback or of a feedback canceller operating
- HA whistles in quiet but stop when noise occurs. This is cuz WDRC causes gain to increase in quiet places
- The HA appears to stop working/become weak or distorted. This could be from a severe/profound loss that cant hear the feedback but can detect the decrease in gain to stop feedback
solutions and disadvantages of those solutions for feedback oscillation problems
Make sure theres no excessive peaks (REAG-real ear aided gain). If so, damp them.
• Disadvantage: the peak may be necessary to achieve desired insertion gain
Decrease vent size or go from open dome to closed dome
• Disadvantage: occlusion effect.
Decrease the HF gain or decrease the HF compression ratio or increase the HF compression threshold
• Disadvantage: decrease in intelligibility or sound quality especially for soft sounds
Re-make/re-coat the EM/shell for less leakage (use open-jaw technique)
• Disadvantage: additional time and $$$. Potential occlusion effect, potential EM/shell discomfort, uncertainty of outcome.
Check feedback cancelling algorithm and increase the strength if possible
• Disadvantage: Time and money; uncertain effectiveness
Change to a HA that better enables feedback to be managed by reducing the gain @ those input levels and/or freq that are giving rise to feedback oscillation.
• Disadvantage: Additional time and expense, uncertain effectiveness, reduced intelligibility @ low levels
What can cause problems with tonal quality and what are some common words used to complain about it?
excessive HF amp or insufficient LF amp. (shrill, harsh, hissy, sharp, metallic, tinny); excessive LF (muffled, unclear, boomy, dull)
what are three complications of changing the balance of high-to-low frequency gain when adjusting tonal quality?
- Excessively peaky gain curve can produce similar comments
- Tonal quality may be unsatisfactory only for low-level, or only for high-level sounds or may apply across all input levels
- Is a shrill sound of a hearing aid: could it be cuz the Pt knows better than the prescription procedure what is best; or is it cuz he/she hasn’t come used to the high freq info since they’ve been deprived.
- —People can take months to learn to fully use HF info that they previously hadn’t: acclimatization effect
what is the acclimatization effect?
• People can take months to learn to fully use HF info that they previously hadn’t
trends of tonal quality problems
- Pts tend to choose gain in the freqs that they don’t have a big loss in probably because theyre used to hearing those sounds. A compromise is to provide Pts with a response that is mid-way btwn the response they prefer and the response that is believed to be best for them
- Another solution is for the gain to automatically, but gradually increase in the months following fitting. This is called automatic adaptation.
what could be the problem if the HA is noisy in quiet places? solutions?
- Could be because the internal HA noise is being amplified sufficiently to be audible OR it may indicate that noises in the environment are eing amplified and the patient hasn’t realized that these are noise that everyone else can hear.
- If the problem is amplification of low-level sounds in the environment, identify the noise source to the patient and explain that normal-hearing people can also hear these sounds and they are part of the richness of life. (explain that the sounds will eventually become less noticeable)
- If the problem is internal noise, ensure that the aid is w/in specs by measuring in a test box.
what is the solution when soft speech in quiet places cannot be understood?
• Solution is to provide more gain for low-level sounds. This may cause increased possibility of feedback and amplification of sounds that the Pt doesn’t want to hear.
what is wrong when the HA is sometimes too loud when noises occur?
(this complaint requires careful questioning)
• If the noises ever get so uncomfortable that the Pt HAS to immediately turn the volume control down or the HA off, the OSPL90 of the hearing aid must be decreased. Decrease gain, increase damping, or with electronics.
• If the patient CAN tolerate the noise, but would rather it was not so loud so often, a change to the input-output characteristics can improve the situation markedly.
When Background noise makes it hard to understand speech
(effect noise has on intelligibility, or fatigue caused by strenuous listening)
• If the offending noise has a spectrum that is markedly different from that of speech, ensure that adaptive noise reduction is enabled, or increase its strength if already enabled.
• If the noise has a spectrum similar to that of speech, (usually the case.) and if speech is loud enough/good tonal quality, then intelligibility can be improved only by using an effective directional mic. Or remote mic w/ wireless transmission
What if…People in the distance are easier to understand than people nearby
- Compression could start if people next to you are very loud.
- Solution is to increase max output or change from peak clipping to compression limiting.
Noise levels rising and falling intermittently is because…?
- Compression release times can cause background noise levels to rise during gaps w/in speech, or after brief impact sounds have forced the gain down.
- Solution is to use faster compression (rise in level seems instantaneous) or slower compression (so in brief gaps the rise level is smaller, long gaps its slow and change is less noticeable.
Hearing Strategy Types
- watch the talker - lips, face, body
- find out the topic
- ask the talker to speak clearly
- ask the talker to gain your attention
- give frequent feedback
- ask specific questions
- guess meaning and repeat to confirm
- get close to the talker
- get rid of noise
- discuss clear speech with significant others
