Fitting Frequency Compression Hearing Aids to Kids: The Basics Presenters: Susan Scollie and Danielle Glista Presented at AudiologyNow! 2011, Chicago
Support This work was supported by: Canadian Institutes of Health Research, National Science and Engineering Research Council, Masons Help-2-Hear Foundation and Phonak AG Special thanks to: Richard Seewald, Vijay Parsa, Melissa Polonenko, Marlene Bagatto, and Jacob Sulkers for their contributions
Presentation Overview 1. How does frequency compression work? 2. Overview of current research 3. Case studies and discussion 4. FAQs
Review of Terminology Frequency compression (FC) parameters: Cut-off The frequency at which compression begins Ratio Determines how much compression is applied Note: These are adjusted together in Phonak software (e.g., Phonak SoundRecover ) Glista, Scollie, Polonenko and Sulkers(2009), Hearing Review
What does FC look like? Below cut-off Above cutoff Frequency (Hz) High-frequency sound in compressed into a smaller bandwidth This doesn t mean we lose some high-frequency energy, rather it is lowered in frequency We need verification tools to help us learn more about the effects of FC on each hearing aid fitting
What does FC look like? Below cut-off Frequency (Hz) High-frequency sound in compressed into a smaller bandwidth This doesn t mean we lose some high-frequency energy, rather it is lowered in frequency We need verification tools to help us learn more about the effects of FC on each hearing aid fitting
Evidence to consider: Studies on bandwidth: Does it matter if we provide audibility of high frequency speech cues to children who use hearing aids? Are we providing these cues? Electroacoustic information: What is the signal processor doing to speech? Can we measure that? Behavioural studies of outcome: Is there benefit when we apply this processing strategy?
Bandwidth matters for kids Children need access to the high frequency sounds of speech, to understand and monitor speech production: But: See: Moeller et al, 2007, a review article by Stelmachowicz et al (2004), Pittman 2008, and various other studies I`ve only mentioned a few here. If audibility cannot be provided via the available bandwidth and gain/output, is it beneficial to lower the cues to an audible frequency range?
Studies of bandwidth: Stelmachowicz et al 2001 NH listeners: 6000 Hz seems adequate. HI listeners: more than a 6000 Hz bandwidth was needed in this study.
Studies of bandwidth: Pittman 2008 Faster word learning with extended bandwidths. 4000 Hz versus 9000 Hz, using lab equipment.
Bandwidth limitations for severe losses: Hearing Aids A and B are both modern devices, and are at maximum settings in this region. Hearing aid responses and targets for speech (input at 65 db SPL) A severe sloping loss. Both fall below threshold above 2000 Hz (speech peaks are audible to about 2500 Hz not shown).
Results from Studies with Children
Initial field trial: Glista et al. (2009a) 24 patients: 11 children and 13 adults A wide range of hearing losses sloping from mild through profound.
UWO test battery: Consonants (subset) DFD Test (Cheesman & Jamieson, 1996) atil
UWO test battery: Plurality UWO Plurals Test Crayon Crayons
UWO test battery: Speech sound detection Ling-6 Sound Test mmm ooo aaa sss eee shh
Results: Recognition of consonants, plurality, vowel sounds (adults and children) Improvement Improvement
Results: Individual kids
Results: Speech sound detection
Audiometric & age candidacy. Significant predictors of outcome: Age group (adult versus child) Better ear high frequency pure tone average The lowest frequency at which the audiogram had a severe loss (drop off frequency) db HL db HL Frequency 100 1000 10000-20 0 20 40 60 80 100 120 Frequency 100 1000 10000-20 0 20 40 60 80 100 120
Follow-up study: Glista et al. (2009b) The FC processor was included in a commercial product & labeled SoundRecover. Our participants, who at this time had been wearing prototypes for > 1 year, were called back in to have their aids replaced with commercial devices & retested.
Participants and design 10 child participants from the Glista et al. (2009a) study Devices: Study 1: Savia 311/411, modified to include prototype NFC (labelled as NFC 1 and NFC 2) Study 2: Naida V SP/UP with SoundRecover NFC (labelled as Naida) Same test battery
Results: Consonant recognition 100 Improvement Consonant Recognition score (percent correct) 90 80 70 60 50 40 30 NFC 1 No-NFC NFC 2 Naida Study Phase
Results: Plural recognition 100 Plural Recognition score (percent correct) 90 80 70 60 50 40 30 NFC 1 No-NFC NFC 2 Naida Study Phase
Recent research: Wolfe et al. (2010) Evaluated FC with a different hearing loss population PTAs mostly in the moderate-moderately severe range Conclusions: Significant speech perception benefit reported at the group level (test battery: UWO Plurals test, ling sounds, Logotome test) No difference in noise on BKB-SIN when comparing with/without FC
UWO Pediatric Fitting Protocol
Overview 1) Provide more audibility of high-frequency cues than is possible with a well-fitted device We evaluate the frequency response based on a DSL v5 child fitting to first maximize the bandwidth of the fitting without frequency lowering 2) We verify using measures that show us audibility of specific high frequency speech bands
FC Verification protocol: Adopted from: Glista & Scollie (2009) in AudiologyOnline 1. Verify the shape and gain of the fitting without FC active To ensure that the LTASS for multi-levels sounds has been fit-to-targets 2. Verify the maximum power output (MPO): To ensure that high level sounds are limited appropriately MPO measurements are not valid above cutoff frequency Can disable SoundRecover to measure MPO at all frequencies 3. Start with the default FC setting Assess the need for FC by estimating high-frequency audibility with and without FC active 4. Measures of frequency-specific speech bands and live speech production can help evaluate: The amount of lowering that has been applied to the signal The approximate sensation level of high-frequency regions of speech The potential for speech sound confusions 5. Perform a listening check: Consider sound quality judgments from the listener as well as the clinician 6. Repeat steps when fine-tuning of the FC setting is required (e.g., fine-tuning away from the default setting for a steeply sloping losses)
Sample fitting: Sloping hearing loss Enter audiometric data on verification system Choose an appropriate hearing aid for the child s loss (example shown: Phonak, Naida SP) Adjust fitting to meet targets (example shown: DSL v5.0)
Can we improve this fitting with FC? Audibility is better here Audibility is limited here
Live speech (without and with FC) shhhh ssss Q: Does the frication bandwidth or peak frequency change when FC is activated? shhhh ssss No Frequency Compression With Frequency Compression
Measures of live speech: Pros and Cons X Not a calibrated measure (level will vary according to vocal effort) Tells us about change in the frequency location of naturally produced speech sounds (this will vary according to talker) Provides a realistic view of the frication bandwidth
New clinical tests High frequency speech band Level - Low frequency speech energy Notch (empty area) Frequency - The Audioscan Verifit offers filtered speech stimuli that allow us to test the effects of FC These can be run with & without FC using bands of energy around: 3.1, 4k, 5k or 6.3kHz
Filtered speech bands (without and with FC) 4000 Hz 6300 Hz Q: What FC effects can we see with this sort of measure? 4000 Hz 6300 Hz No Frequency Compression With Frequency Compression
Filtered speech bands: Pros and Cons Calibrated in level Tells us about change in frequency location (can help us estimate sound overlap) X Does not provide a realistic view of the frication bandwidth (only narrow bands of speech)
Time for Case Examples
Fine-tuning with filtered speech bands Let s try FC 4000 Hz without FC 6300 Hz without FC Is the default enough? No FC 4000 Hz with FC 6300 Hz with FC The best we can do 2400, 4:1 4000 Hz with FC 6300 Hz with FC 1600, 4:1
Live Speech with FC The shoulder of this /s/ s o u n d s i s l i k e l y a u d i b l e /+/ Live /+/i s b r o a d e r i n b a n d w i d t h & /s/
Recognition of plurality - Before/after acclimatization to FC Further details available from Glista et al. (2011), Proceedings from Sound Foundations 2010 Baseline Treatment Withdrawal Improvement Time course
Discrimination of /s- / UWO Speech Discrimination Task
Case 1: Implications Fine-tuning of the default SoundRecover setting was required for this hearing loss configuration Significant speech perception benefit was reported with FC, compared to without This child benefitted from an acclimatization period with FC processing Outcome measures completed before and after an acclimatization period allowed for careful observation speech perception performance over time
Case 2: Fitting with partial audiometric information
Default NLFC setting Cutoff Frequency is here, so no frequency lowering within the range of measured thresholds. This is probably good. The frequency compressed band lies above the range of measured thresholds. Assuming a sloping loss, it may be audible (or not!).
Same setting with speech bands 4000 Hz without FC 6300 Hz without FC 4000 Hz with FC 6300 Hz with FC No FC FC: 2800, 4:1 (default)
Case 2: Implications This case doesn t provide answers but does illustrate the challenges of fitting with partial audiometric data. Most fittings include at least in-the-brain interpolation & extrapolation. Suggestions: Don t use frequency lowering to move the signal into the range of measured thresholds in this case that would be below 2000 Hz, and would likely be excessive. Some clinicians disable until more is known, some fit on their expectation of where the audiogram will be. Some make this decision depending upon the severity of loss (enable if severe). All of these are reasonable strategies until more evidence is available.
Case 3: The importance of fine-tuning
All tests show that the frequency lowered bands are inaudible 4000 Hz 6300 Hz shhhh ssss
We fine tuned results below: 4000 Hz 6300 Hz shhhh ssss
And the winner is Test Percent Correct Score Setting 1 Percent Correct Score Setting 2 Interpretation Nonsense syllables 56% 69% Discrimination of S/ SH 37% 65% Significant improvement with the revised setting Significant improvement with the revised setting
Case 3: Implications Speech based outcome measures can assist in NLFC fitting and fine-tuning Allow you to compare performance at different settings and/or with/without NLFC active For this case, the verification results directly support speech perception results a stronger setting helped this child s speech perception ability
FAQS
1. When should I enable FC in a fitting? Some important considerations: 1. Is the listener receiving sufficient audibility across frequencies without using frequency lowering? Start with a scientifically based prescriptive method to assess fit-totargets (i.e., provide as good of a fitting as possible without NFC enabled) 2. Have you verified this using appropriate techniques? (e.g., using advanced verification techniques) 3. Consider the literature! Aim to provide audibility of energy well above 4000 Hz for developing infants & children (refer to start of presentation) what we can accomplish with conventional amplification is ever evolving!
2. Should we be providing asymmetrical NFC settings? UWO findings presented thus far include symmetrical NFC settings only (i.e., the same NFC setting in each ear, with the exception of one published case) This included fitting NFC based on better ear thresholds What would an asymmetrical NFC setting mean for the listener? They would be receiving asymmetrical frequency allocation between the two sides Can the listener adapt to this? We need more research to directly evaluate how this will affect speech understanding
3. Is it ok to enable NFC for mild to moderate hearing losses? Studies on this topic have included listeners with mild to moderate PTA values and significantly more hearing loss in the high-frequencies (i.e., moderately severe to profound in the high-frequencies) We do not have any evidence suggesting that NFC technology should or should not be used in cases presenting with a mild amount of hearing loss in the high-frequencies Think back to FAQ #1 Aim to provide FC in the case where a conventional fitting cannot provide sufficient audibility of high-frequency sounds Err on the side of providing frequency compression to only the highest frequency part of each fitting Further research is needed - for discussion on this topic refer to: Scollie (ASHA Division 9, 2010), Wolfe et al. 2010