Fitting Decisions and their Impact on Hearing Aid User Benefit. Mallory Maine, AuD Audiologist, GN ReSound

Transcription

1 Fitting Decisions and their Impact on Hearing Aid User Benefit Mallory Maine, AuD Audiologist, GN ReSound

2 Agenda Common Fitting Oversights #1 Setting the coupler type in fitting software To set or not to set? #2 Taking fitting ranges at face value Where s the gain? #3 Reducing more than feedback Why calibrate? #4 Overprescribing directionality We can t get enough, but is it ever too much?

3 Oversight #1: Setting the Coupler Type in Fitting Software

4 Understanding the Display Open and closed configurations Vent effects

5 Understanding the Display Configured as Open with Dome Configured as Closed with No Vent

6 Investigation REMs of various RIE coupling options Hearing instruments on with low gain to visualize coupling effects on gain All hearing instrument features off and mics to omni 55dB speech noise

7 Real ear db SPL Effects on Gain open dome tulip dome power dome custom earmold Frequency (Hz)

8 LF Gain for Power Dome vs. Custom mold Muller & McBride, 2012

9 Findings We know that changing the physical coupling to the ear will effect primarily the low frequency gain.

10 Trivia Back to the fitting software What does it need to know? Question: Which will affect the hearing instrument gain settings? A. if it s an open or closed fitting B. vent size C. the exact coupling to the ear D. All of the above

11 Question: Which will affect the HI gain settings? Trick question because really it depends on the fitting software!

12 Investigation Coupler measurements of RIEs Compare gains of most open to most occluding vent settings available in software Set features off and mic to omni on all instruments Programmed with N3* audiogram Hz k 1.5k 2k 3k 4k 6k HTL *Bisgaard et al, 2010)

13 Gain for occluding option minus gain for open option (db) Changes in Closed to Open 20 Effect on hearing instrument gains of changing from occluding to open fitting: Approach Frequency (Hz) ReSound Manufacturer "Physical 1 Properties" Starkey Manufacturer "Acoustic 2 Options"

14 Gain for occluding option minus gain for open option (db) Changes in Open to Closed 20 Effect on hearing instrument gains of changing from open to occluding fitting: Approach Frequency (Hz) "ReSound Manufacturer reconfigure" 3

15 Gain for occluding option minus gain for open option (db) Changes in Open to Closed Effect on hearing instrument gains of changing from open to occluding fitting: Approach Frequency (Hz) Oticon Manufacturer "Acoustics" 4 Phonak Manufacturer "Acoustic 5 Parameters" "Siemens Manufacturer Acoustical 6 Parameters"

16 Findings Three approaches when change from open to closed: 1. Remains the same: gain was not affected 2. More gain for closed: prescribes more gain for closed across frequencies due to ability for usable LF gain and compensation for lost canal resonance 3. More low frequency gain for open- LF gain is boosted for open in an attempt to compensate for roll off and HF are reduced for canal resonance

17 Case Study Complaint FSW display: closed

18 Case Study Complaint It s very sharp sounding and I still don t feel like I m hearing well enough Problem: COUPLING The prescribed gains are different than what the patient is actually getting.

19 Conclusion: Configuration and Vent Effects Manufacturers are different in how these options are treated in fitting software so know your manufacturer No harm in setting them appropriately When in doubt, Verify!

20 Oversight #2: Taking Fitting Ranges at Face Value

21 How fitting ranges are calculated Ingredients: Electroacoustic specs in coupler Real-ear-to-coupler difference + MLE (CORFIG) Fitting prescription Directions: Add CORFIG to coupler FOG to get max insertion gain Plug audios into prescription Build in safety margin based on MSG and to allow VC use and fine-tuning Competitive environment what do other manufacturers publish? Point being.fitting ranges are not standardized

22 Investigation Compare MPO and fitting ranges of similar RIE products Fit with out of the box fitting Measure in coupler with 65dB input

23 Fitting ranges for similar RIE products FOG 46 db MPO 108 db SPL FOG 45 db MPO 108 db SPL FOG 45 db MPO 112 db SPL FOG 50 db MPO 113 db SPL

24 2cc gain (db) First Fit vs. NAL NL 2 40 Moderate audiogram, 65 db input = NAL NL 2

25 The Facts First fit matters more than the fitting range Six manufacturers fitting software did not meet NAL-NL1 or DSL i/o although their rationale was similar or the same. Even without the hearing aid being inserted in the ear, the prescriptive targets of the proprietary formulas are not matching NAL or DSL targets. Keidser, G., Brew, C., Peck, A. (2003). Proprietary fitting algorithms compared with one another and with generic formulas. The Hearing Journal (56). 3,

26 The Facts What does it matter if fitting rules are based on generic rules or not? Might get shorted on reserve gain Why such differences in first fit gain when the fitting rule is supposed to be based of generic rules? The fitting rule and non audiometric settings.

27 Example of Non-audiometric Settings: Experience Level A. Proprietary Experienced Non-linear (reference gains) B. Proprietary Experienced Linear Slightly HIGHER target gains C. Proprietary First time User Slightly LOWER target gains D. Proprietary Comfort User Much LOWER target gains

28 Findings Fitting ranges are not standardized Fitting ranges are only a small part of the fitting First fit varies greatly between manufacturers Fitting rationales maybe based on generic rules but are not the same and may have an impact on reserve gain Non audiometric settings can have a big impact on the targets and therefore the fitting

29 Conclusion: Fitting Ranges Remember to select the desired fitting rule in the FSW When looking at a fitting range be sure to not cut it too close Consider non audiometric setting effects When in doubt, verify!

30 Oversight #3: Reducing More than Feedback

31 The Basics Static: the feedback path created with the hearing instrument in the wearer s ear. Includes leaks, vents, ear canal, and device components Dynamic: the feedback paths created when the static path is altered as in using the phone or placing something near the hearing aid We need to manage both.

32 Feedback paths Closed ear mold Vented ear mold 1/2

33 Filters Constrained adaptation Kates, 1999

34 Filters Clamping If the actual feedback path measurement is not available A reference filter is applied and constraints based on the reference At times the reference constraints become inadequate When instability is detected gain is reduced

35 The Goal Abate feedback while maintaining gain and without artifact But how do you know if you are achieving the goal?

36 Investigation REIG measures completed with comparable 6 RIEs (n=40ears) Static assessment: Compared the amount of gain with feedback management on and off Dynamic assessment: Compared the amount of gain with feedback management and with and without phone to the ear

37 Now you see it now you don t

38 D1 D2 D3 D4 D5 D6

39 Findings Dynamic feedback can vary +/- 10dB from the static path Gain reduction (clamping) is used to eliminate dynamic feedback that is outside the constrained filter Some gain reductions are greater than others

40 Possible Complaints I hear quick bursts of feedback when the car door dings Inaccurate calibration Over prescribing feedback management settings I can hear fine normally but now that the settings were changed to control feedback I have really difficulty on the phone Over prescribing feedback management settings Using a system with greater amount of gain reduction

41 Conclusion: Calibration Calibrate the instrument when required or recommended by the manufacturer to create a proper template for the feedback management system Set the parameters in the FSW with caution and do not over prescribe to avoid artifact Measure to find out what the system is really doing

42 Oversight #4: Overprescribing Directionality

43 Two ears send distinct information to the auditory cortex of the brain to create a complete, rich and accurate portrayal of the auditory environment.

44 How the Brain Processes Sounds in the DETECT Environment CHOOSE A new sound in the environment draws your attention. Example: The sound of a candy wrapper during a lecture. Filtering out sounds until you hear only what you want to hear. Example: Your child s laugh amongst other children at play in a park. Top down Bottom up

45 User Preference: Binaural Omni & Directional Modes with Manual Switching 22.3% Omnidirectional 77.7% Directional Cord M, Surr R, Walden B & Olson L. (2002). Performance of directional microphones in everyday life. Journal of the American Academy of Audiology, 13:

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47 Bentler et al, 2004 Results Results No significant difference between directional and Monofit fittings (p<.05) Cord et al (JAAA, 2007)- 12 subj, lab trial, in agreement

48 Let s review a few analogies

49 Some Collaborative Directionality Systems cut out the front and back view to listen on the side

50 And some Collaborative Directionality Systems cut out the front and sides to listen to the rear

51 Now, awareness of the entire environment to make informed choices

52 Okay now back to the hearing instrument and directionality

53 Dinner with Family and Friends Secondary Signal Primary Signal of Interest

54 Example A: Maximizing Audibility and/or SNR through Directionality Goal: Prioritizes the ear with the better speech signal when there is loud noise to one side. If there is a difference in signal-to-noise ratio at the two ears, the hearing aids will exaggerate the difference in gain and noise reduction at the two ears to enhance the ear with the best SNR.

55 Example B: Maximizing Audibility and/or SNR through Directionality Goal: Find the strongest speech and increase audibility and/or SNR The hearing instrument detects the direction of the dominant speech signal (front, side, or back) and automatically adjusts the focus direction when the signal source direction changes Possible configurations are bilateral front-facing directional, bilateral back-facing directional, or omni to one side with streaming of the sound on that side to the other ear

56 Findings Listeners prefer omni mic mode in most listening situations The auditory system needs awareness to sounds other than those that are in the look direction in order for the listener to choose the signal of interest Mic settings other than bilateral directional result in comparable SNR improvements along with environmental awareness

57 Possible complaints I am hearing the person next to me more than those in front I hear those in front very well but not those surrounding me I can t hear when someone comes up behind me I can hear the hearing aid changing in noise Add an omni program or an adaptive setting with omni abilities Set directional switching to a less aggressive parameter Asymmetric mic settings

58 Conclusion: Directionality For a basic or everyday program consider a setting that provides omni directional option Consider the patient's listening situation and intent for the program when prescribing directionality

59 Oversights and Solutions! #1 Setting the coupler type in fitting software To set or not to set? It depends on the manufacturer but it is safer to set than not because they could affect gain settings. #2 Taking fitting ranges at face value Where s the gain? Fitting range calculations are not standardized. Once the fitting rules and non-audiometric settings are factored in you might come up short. When looking at the fitting range leave plenty of reserve gain. #3 Reducing more than feedback Why calibrate? Calibration creates a template for feedback cancelation which will limit artifacts and clamping. Know your feedback manager to ensure large gain reductions are not taking place. #4 Overprescribing directionality We can t get enough, but is it ever too much? Yes, in certain cases default directionality is not ideal. Be sure to talk with the patient to assist in the selection and provide an omni setting for day to day use.