Aud 710 Hearing Amplification Exam 2

Front 1

Analog- programmable

Back 1

Computer interface: adjusted with interface + computer software or stand-alone programmer.
More precise that analog non-programmable.
Disadvantages: adjustments not as precise as digital. Limited adjustments available. Advanced processing not available.

Front 2

Digital- programmable

Back 2

Analog transducers (mic, receiver, t-coil).
Digital processing: converts electrical voltages to digital (numbers).
Advantages: potentially the best precision (if mid- to high- end). Advanced processing available.
Limitations: low-end digital has limited adjustments (but cheap!) Additional distortion if not well designed.

Front 3

Feedback strategy: notch filter

Back 3

Aid detects oscillation and then puts in a notched filter at the frequency of the oscillation (feedback).
Disadvantage: reduces gain of input signal (e.g. speech).

Front 4

Feedback strategy: feedback cancellation

Back 4

Aid detects oscillation (feedback). Aid generates signal 180-degrees out of phase. Partially cancels feedback. Allows for an additional gain of approx 10 dB without feedback.

Front 5

Expansion

Back 5

Minimizes amount of amplification below compression threshold.
Why use expansion? Reduces microphone noise and low-level environmental noise.
Expansion is for very low inputs (e.g. 20 dB).

Front 6

Modulation-based noise reduction

Back 6

Speech= slower rate, larger depth (deeper)
Noise= faster rate, smaller depth (shallower)

Front 7

Fitting range for skeleton earmolds

Back 7

Less than 60-65 dB

Front 8

Fitting range for full shell earmolds

Back 8

Greater than 60-65 dB

Front 9

Hard (Acrylic) earmolds

Back 9

Advantages: durable, easy to modify, inexpensive.
Disadvantages: may be more prone to feedback, slight risk of harm from breakage (especially kids).

Front 10

Soft earmolds

Back 10

Advantages: comfortable when tight fit needed, less prone to feedback than hard, no risk of breakage in the ear.
Disadvantages: difficult to modify and change tubing, discolors, hardens, less durable than hard - more frequent replacement.

Front 11

Hypoallergenic earmolds

Back 11

Silicone (semi-soft): low incidence of allergic reactions, very difficult to modify, cannot glue tubing.
Poly-ethylene (hard): best choice for hypoallergenic application, easy to modify (grind, drill), ugly!

Front 12

Earmold acoustics: venting

Back 12

Venting: some of the amplified sound escapes through the vent (mostly low frequencies) smaller vent --> less sound gets out. Some sound comes trough the vent (mostly high frequencies) smaller vent --> less high frequencies get in.
Diagonal (side branch) vents: decrease high frequencies - up to 10 dB above 1 kHz. Intersection close to outside worse b/c increase likelihood of feedback.

Front 13

Earmold acoustics: dampers

Back 13

Dampers: "to decrease gain and max output at frequencies corresponding to resonances in sound bore."
Placement: earmold tubing (BTE), earhook (BTE), sound bore (ITE).

Front 14

Earmold acoustics: sound bore

Back 14

Varying diameter of sound bore affects high frequency response > 2 kHz (primairly 3-6 kHz). The larger the diameter, the more gain in the high frequencies.
Two ways: Acoustic horn- maximum 9 dB better than standard tubing. Large diameter bore- maximum 6 dB better than standard tubing.

Front 15

Candidacy factors

Back 15

Communication problems: ***self perceived***, perceived by friends/family.
Hearing loss: thresholds, speech recognition.
Lifestyle/communication demands.
Motivation/expectations.

Front 16

Determining Candidacy: Data Used

Back 16

Audiometric data: thresholds and speech recognition.
Information from interview.

Front 17

The interview

Back 17

Communication difficulties?
-Situations, frequency, severity.
-Open-ended or probing questions: Why are you here today?" "Tell me about situations in which you have trouble hearing."
-Watch for signs of denial.
Listening environments encountered?
-Leading questions: Do you socialize much? In what setting? Environments?
-Ability and support
-Motivation. Self vs. others.

Front 18

COSI

Back 18

Client Oriented Scale of Improvement. Disability-based. Evaluate the extent to which the patient is having difficulty hearing in different situations. Nominate communicative situations targeted for improvement. After fitting: measure BENEFIT (i.e. improvement with aid), evaluate final disability.

Front 19

GHABP

Back 19

Glasgow Hearing Aid Benefit (or Difference) Profile. Evaluates both disability and handicap. Advantages: short and standardized. Includes "goals" section like COSI.

Front 20

Disability Measures

Back 20

Evaluate the extent to which a patient has difficulty hearing in different situations.

Front 21

Handicap Measures

Back 21

Evaluates the patients feeling about the hearing loss (how much is patient prevented from doing what he/she WANTS to DO). Emotional aspect of hearing loss.

Front 22

What is the significance of an average hearing loss (PTA) of 40 dB HL in terms of the frequency of reported problems (based on HHIE)?

Back 22

Most with average hearing losses of 40 dB HL or more report communication problems. Of those with averages losses below 40 dB HL some will report communication problems and some won’t. Depends on the role of communication demands/lifestyle. If the PTA is 40 or more and patient does NOT report communication problems consider possible reasons.

Front 23

Palmer et al. (2009) used one simple question to predict hearing aid uptake. What was this question? Describe the predictive value of different ratings in the prediction of uptake.

Back 23

“On a scale from 1 to 10, 1 being the worst and 10 being the best, how would you rate your current overall hearing ability?”
Results:
75-100% of those with ratings of 1-5 will pursue amplification.
80-100% of those with ratings 8-10 will NOT pursue amplification.
Ratings of 6-7 are somewhere in the middle. The may need more information, counseling, demo ect.
Uptake not well predicted by audiogram.

Front 24

Choosing styles and processing/circuit options

Back 24

Choosing styles: driven by priorities and practical considerations (e.g. dexterity)
Choosing processing/circuit options: match to communicative complaints and communication demands.

Front 25

Early approach to amount of gain used.

Back 25

Mirroring the audiogram.
Knudson & Jones, 1935
Every 1 dB increase in hearing loss requires 1 dB of additional gain.

Front 26

Problems with "Mirroring the audiogram"

Back 26

Tolerance levels exceeded for higher level sounds.
Excessive gain, particularly for Hz with greatest loss.
Why? Increase HL = decreased DR

Front 27

Two general approaches to gain

Back 27

1) Threshold-based approaches
-Gain and maximum output based on pure-tone thresholds.
-e.g. NAL, DSL, POGO ect.
2) Loudness-based approaches
-Gain and maximum output based on loudness (MCL, UCL, full scales)
-e.g. Pascoe, 1978

Front 28

Prescriptive fitting

Back 28

Should be considered a "starting point"
"Fine tuning" is sometimes necessary to optimize quality

Front 29

Linear prescriptions

Back 29

Appropriate for compression limiting and linear aids

Front 30

NAL

Back 30

"Loudness equalization"
Goal: to maximize speech intelligibility at the preferred listening level of the hearing aid user.
Assumptions: Intelligibility maximized when all frequency regions at equal loudness. Preferred listening levels of real patients correspond to MCL.
NAL perscriptions -- based on pure-tone threshold.

Front 31

What is the difference between speech levels in dB HL and dB SPL when presented though speakers? headphones?

Back 31

dB SPL is 12.5 dB higher than HL levels is presented through speakers.
dB SPL is 20 dB higher than HL levels presented through earphones.

Front 32

Frequency response shaping considerations

Back 32

-Shape of normal loudness curve (mid-level)
-Shape of speech spectrum
-Shape of hearing loss

Front 33

Describe the essentials of the original NAL prescriptive approach

Back 33

For mild-moderate HL – roughly based on half gain rule. Gain at 1000 Hz is equal to 0.46 times the loss at 1000 Hz
For severe-profound loss – need more gain (2/3 gain) at 1000 Hz

Front 34

Describe the research evidence demonstrating validation of NAL-R (Byrne and Cotton, 1987; 1988)

Back 34

Approximately ¾ of listeners judged NAL-R to be as good as or better than the alternative frequency responses and the average preferred listening levels were within 1 dB of prescribed.

Front 35

Describe of how and why NAL-R was modified further for severe-profound hearing losses

Back 35

Went from NAL-R to NAL-RP because they needed more gain. 2/3rds instead of ½.

Front 36

Why can't you use half gain rule to estimate NAL-RP?

Back 36

The ½ gain rule substantially overestimates NAL-RP in low frequencies – that is, the ½ gain rule prescribe TOO MUCH low frequency gain.

Front 37

Explain the concept of loudness equalization as it applies to the goals of the NAL prescription

Back 37

You need different phon magnitude to equal the same level of dB SPL.
Example: 40 phon curve (standard = 1000 Hz @ 40 dB SPL
Mid frequencies require approximately equal intensity level for equal loudness to a 1000 Hz 40 dB tone.
Lower frequencies e.g. 100 Hz, intensity must be raised by approximately 10 dB in order to produce equal loudness to a 1000 Hz 40 dB tone.
As the phons increase (i.e. dB SPL for 1000 Hz increases), the equal loudness contours flatten out more.

Front 38

LTASS

Back 38

Long-term average speech spectrum.
The level of speech across different frequencies when averaged over a long period of time (e.g. 30 seconds or more).
Characteristics: The LTASS has more energy in the low frequencies. 6 dB/octave drop above 500 Hz.

Front 39

Goals underlying the NAL-NL prescription (for WDRC aids)

Back 39

1) Amplify relative loudness of different speech band to maximize intelligibility.
2) Loudness control: amplify so that sounds are no louder than normal hearing person perceives at same level.
3) Does not attempt to "normalize" loudness.

Front 40

Loudness normalization

Back 40

Amplify sound so that at any input level and frequency, the hearing aid wearer would report loudness to be the same as that which a person with normal hearing person would report.

Front 41

Similarities between NAL-NL1 and NAL-NL2

Back 41

Note: NAL-NL2 not yet fully released.
Same prescription of maximum output.
Same allowance for number of channels.

Front 42

5 main changes made in NAL-NL2 (compared to NL1)

Back 42

1) Less gain than NAL-NL1 above 65 dB (people prefer less gain)
2) Gender correction (females prefer 4 dB less gain)
3) Acclimatization (experience) correction (-2 dB on average for new users)
4) Binaural correction changed (less than NAL-NL1)
5) Greater gain for children with congenital HL at low input levels

Front 43

The empirical basis (research studies) for the DSL gain targets.

Back 43

These targets were based on a study by Erber and Witt conducted to determine how sensation level affected speech understanding for a group of children with severe hearing loss. They determined the sensation levels that maximized the ability to understand speech. The DSL developers based their "desired sensation levels" on the levels that were found to maximize speech understanding in the Erber and Witt study. They then determined that the target levels were within the comfort range based on a study of preferred listening levels of children with hearing loss.

Front 44

How did DSL developers arrive at their maximum output targets?

Back 44

The developers based MPO targets on the adult norms for loudness discomfort levels. They set the targets 1 standard deviation below the adult norms for loudness discomfort and then made slight additional adjustments for upward spread of masking.

Front 45

Describe differences between frequency responses prescribed by DSL and DSL[i/o] v.5 and NAL-NL1 (linear/compression limiting Rx)

Back 45

Flat losses: DSL and DSL[i/o] prescribe more in the high and low frequencies than NAL-NL1.
Sloping: DSL and DSL[i/o] prescribe more gain in the high frequencies than NAL-NL1. The steeper the slope, the larger the difference in HF gain between DSL and NAL prescriptions.

Front 46

Loudness control:

Back 46

Amplify so that sounds are no louder than normal hearing person perceives at same level.

Front 47

Loudness scale

Back 47

Give the patient a list and tell them to identify which category the sounds presented fall into (usually use bottom 7 categories)
Painfully loud
Extremely uncomfortable
Uncomfortable loud
Loud, but OK
Comfortable, but slightly loud
Comfortable
Comfortable, but slightly soft
Soft
Very soft

Front 48

Consequences of setting OSPL90 too high or too low

Back 48

Too high: loudness discomfort and further damage to hearing.
Too low: HA user does not receive sounds at adequate SL and excessive saturation.

Front 49

Approaches to setting max output level: approach 1

Back 49

Based on direct measurements UCL.
Decide on a loudness procedure: categorical rating of loudness, ascending procedure, practice effects associated with loudness measures - stabilize by 3rd trial. Otherwise people underestimate.

Front 50

Approaches to setting max output level: approach 2

Back 50

Prescriptive method.
There are consequences for setting OSPL too high or low.
NAL OSPL prescription: best value of OSPL should consider both discomfort and saturation.

Front 51

The maximum output controversy

Back 51

Position 1: Must base MPO on individually measured LDLs.
LDLs variable. Cannot be predicted by PT thresholds. Implications: HAs problems (discomfort) if LDLs not used.
Position 2: Aid MPO can be prescribed using PT threshold.
LDLs are variable but range of acceptability can be predicted. Must way risk/benefit of prediction vs. LDL measures.

Front 52

NAL OSPL validation study "Pro-Rx"

Back 52

Storey et al. 1998: prescription validated with real subjected wearing aids. Tested aided loudness discomfort to make sure Rx settings did not exceed LDL. Adding LDLs did not substantially improve accuracy of OSPL procedure (only 0.4 dB)

Mackersie (2007): fittings based on NAL OSPL Rx PLUS aided loudness validation at fitting. Unaided LDL measures. Max output (ear canal) exceeded LDL for only 1/29 and this person did not want his aid adjusted. Conclusion - LDL not worth the time.

Front 53

NAL OSLP validation study "Pro-LDL"

Back 53

Shi et al. (2007): fewer adjustments (average 1 less) when LDLs measured. BUT used (unvalidated) DSL [i/o] Rx, not NAL.

Munro & Patel (1998): Correlation between amount by which max output exceeded LDL and reported loudness problems. BUT no information about how MPO determined - NAL Rx not yet developed.

Front 54

How do you modify gain/frequency response targets for a conductive/mixed HL.

Back 54

Gain frequency response prescriptions: prescribe 1/2 gain for SN part of the loss. Prescribe additional gain at each frequency equal to 75% of the conductive loss (ABG).
OSLP: prescribe OSLP for SN part of loss. Increase OSLP by adding 87.5% of the ABG.

Front 55

Four general binaural effects that enhance hearing

Back 55

Localization
Loudness Summation
Diffraction
Noise

Front 56

Binaural effects: Localization

Back 56

Horizontal localization: depends on time and intensity differences between ears. Impaired localization may contribute to difficulty in noise. Won't be able to change listeners quickly or follow moving sound.
Vertical localization: depends on high frequency spectral cues. Binaural hearing is less important for vertical localization.

Front 57

Binaural effects: Loudness Summation

Back 57

Loudness greater when using two ears compared to one. Near thresholds loudness summation = 3 dB. At comfortable level loudness summation = 5-6 dB.

Front 58

Binaural effects: Diffraction

Back 58

Head diffraction. The head is getting in the way of sounds coming at the head from an angle other than directly in front or behind. High frequencies are less able to travel around the head than the low frequencies are. High frequencies more affected by diffraction. For binaural hearing you must simply attend to the ear with the better SNR. For unilateral hearing there is a disadvantage if good ear is on side of noise.

Front 59

Binaural effects: Noise

Back 59

Squelch effect in background noise. Understanding speech is easier with 2 ears due to the central auditory system effect. "Binaural masking level difference" - subtracts sound from side with poorer SNR. May be due to squelch effect.

Front 60

Binaural advantages

Back 60

Speech perception (speech in noise)
Localization
Tinnitus relief
Avoid late onset auditory deprivation

Front 61

Binaural advantages: Speech Perception

Back 61

It has been demonstrated that people with binaural hearing aids have better speech understanding than those with a monaural fitting (depending on how speech intelligibility is measured). Speech intelligibility effected by: head diffraction affect and binaural squelch effect.

Ross (1980) review of laboratory studies: found that 15/19 studies showed bilateral speech advantage. 4 showed no difference. None showed unilateral advantage.

Bilateral advantage- robust for moderate HL or greater. For mild HL the advantages of binaural hearing aids are less obvious because they are getting some speech signal without aids.

Front 62

Binaural advantages: Localization

Back 62

Horizontal localization: greater advantage for moderate to severe loss than for mild loss.
Vertical localization: no binaural advantage with BTE, ITE or ITC. There may be some advantage with CIC because the pinna, which helps with localization, is not filled with an earmold.

Front 63

Binaural advantages: Tinnitus relief

Back 63

Brooks & Bulmer (1981) found that 66% reported tinnitus decrease with 2 aids. Only 13% reported tinnitus decrease with 1 aid. More sound from the outside may distract from tinnitus,

Front 64

Binaural advantages: Avoid late onset auditory deprivation

Back 64

Unilateral fittings: the ability to understand speech may decrease in the unaided ear overtime. May be accompanies by small increase in speech recognition in aided ear. Magnitude of reduction varies by study, mean = 7%. Recovery following bilateral amplification in many (2/3), but not all patients.

Front 65

Potential disadvantages of bilateral hearing aids

Back 65

Cost
Binaural interference: small portion of elderly. Possibly due to inter-hemispheric transfer of information across the corpus collosum.
Self-image: people think they look twice as disabled with two hearing aids. Usually people who are more resistant to wearing hearing aids to begin with.

Front 66

Four goals to consider for a monaural fitting

Back 66

1) Maximize range of sounds audible to person.
2) Maximize range of sounds available to binaural interaction.
3) Send high quality signals to the brain.
4) Try to make overall hearing as “normal” as possible.

Front 67

Monaural "rule-of-thumb"

Back 67

Fit the ear that has four frequency average (.5, 1, 2, 4 kHz) closer to 60 dB HL.

Front 68

Which HA configuration is best?

Back 68

Bilateral except for:
Small number of people with binaural interference.
Small number with unaidable hearing in poorer ear.

Front 69

How much benefit does binaural provide?

Back 69

Moderate to severe loss: substantially more benefit than monaural. A person with two aids can tolerate 5 dB more noise to the the same speech understanding as with one HA.
Mild in at least one ear: small benefit.

Front 70

Describe the general research findings comparing compression limiting and linear (peak clipping) output limiting for profound losses. What general recommendations does Dillon make in light of this research?

Back 70

Earlier evidence against CL for profound
Preference: Half subject with PTA > 90 dB preferred linear over compression (Dawson et al., 1991)
Recent evidence in favor of CL
Most with profound HL prefer compression over linear (Barker et al., 2001)
Conclusions: peak clipping if Hx use with max volume.
Dillon recommends using peak clipping if the patient has a history of preferring maximum volume control settings or complains that the aid does not make sounds loud enough. Otherwise use compression limiting.

Front 71

Describe the general findings of research comparing findings for linear, compression limiting and WDRC at average input levels. Include both speech recognition and preference results.

Back 71

Speech recognition at average conversations levels
No difference between speech recognition for linear, compression limiting, WDRC
Preferences
No difference between preferences for linear, compression limiting, WDRC at average input levels (65 dB SPL)

Front 72

Describe the general findings of research comparing speech recognition for linear/compression limiting vs. WDRC at low input levels.

Back 72

Speech recognition at soft input levels is better for WDRC than for CL or linear
Why? WDRC -- increased gain for soft inputs compared to CL or linear
Exception: If listeners adjust VC (linear, CL) to increase gain. Compensates for soft input level

Front 73

Describe general research findings (e.g. quality ratings – Dillon, 1988) comparing linear vs compression limiting at high input levels.

Back 73

Increased listening comfort compared to linear (true of any type of compression)
Quality: HI listeners gave CL aids higher ratings for “clarity” judgments than linear aids (Dillon, 1988)