Harvey Dillon Audiology NOW! Prescribing hearing aids for adults and children Prescribing hearing aids for adults and children Adult Measure hearing thresholds (db HL) Child Measure hearing thresholds (db HL or db SPL) Harvey Dillon, Gitte Keidser, Teresa Ching, Matt Flax, Scott Brewer HEARing CRC National Acoustic Laboratories Enter into manufacturer software (hearing aid auto adjusted to approximate prescription) Measure individual RECD (or estimate from age) Enter into manufacturer software (hearing aid auto adjusted to approximate prescription) Verify with real ear measurement Audiology NOW! San Diego Adjust amplification to better match prescription Adjust hearing aid in coupler via computer to better match prescribed coupler gain Electrophysiological hearing threshold with insert phones (db nhl) Infant Fitting Procedure Behavioural hearing threshold with insert phones (db HL) Measure individual RECD, (or estimate RECD from age) Prescribe hearing aids to: Make speech intelligible Make loudness comfortable Calculate hearing threshold level (adult equivalent db HL or db SPL in ear canal) Verification of REAG? Evaluation! Apply prescription to derive coupler gain targets Adjust hearing aid via coupler/programmer to achieve coupler gain targets Prescription affected by other things localization, tonal quality, detection of environmental sounds, naturalness. The rationale for NAL proceudres Deriving optimal gains - step Maximize calculated speech intelligibility, but Keep total loudness less than or equal to normal Speech spectrum & level Gain-frequency response Loudness model Normal loudness Compare Intelligibility achieved NAL-NL (999) empirical studies psychoacoustic studies NAL-NL Intelligibility model Amplified speech spectrum Loudness model Loudness (hearing impaired) speech intelligibility models Audiogram
Harvey Dillon Audiology NOW! Prescribing hearing aids for adults and children Overall approach to prescription Limiting compression ratio Psychoacoustics The maximum C Assumptions, rationale Theoretical predictions Final formula 3..5 Ca. 6 Speech science Compare.5. log f 5 Empirical observations H 5 Multi-dimensional equation: A neural network H 5 H 5 H H H 8k SPL Effect of language Gain at each frequency depends on importance of each frequency Low frequencies more important in tonal languages Two versions of NAL-NL Tonal languages Non-tonal languages G 5 G 5 G G G 8k Calculating loudness Loudness model of Moore and Glasberg () Allowance for hearing loss /3 octave SPL 3 Threshold Noise External & middle ear Free field speech level Input to cochlea Filtering into auditory bands Excitation level Calculate loudness per band Loudness per band Sum across bands Total loudness Audibility:... 5... 6... 7... x x x x Importance:...3. = = = =....5....3....5... Freq =.3
Harvey Dillon Audiology NOW! Prescribing hearing aids for adults and children Speech Intelligibility Index Sum SII = A i I i Audibility Importance But intelligibility gets worse if we make speech too loud! Percent Correct 8 6 The transfer function Sentences Nonsense syllables...6.8 Speech Intelligibility Index (SII) Observed and Predicted performance Audibility and Speech intelligibility H.I. - 56 Hz VCV. MF MS SF SS Percent correct 8 6 Proportion correct.8.6. LP7: Q LP7: N LP: Q LP: N LP8: Q LP8: N LP56: Q 36 36 36 36. LP56: N HP8: Q HP8: N HP: Q Sensation level (db).....6.8. HP: N HP7: Q HP7: N Ching, Dillon & Byrne, 998 Calculated SII Deficit = S ansii -SII eff Intelligibility and audibility Percent Correct 8 6 SII eff SII ansi Deficit =.6 -. =. p m...6.8 Speech Intelligibility Index (SII) 3 Sensation level (db)
Harvey Dillon Audiology NOW! Prescribing hearing aids for adults and children BKB, VCV and CUNY Desensitisation for hearing loss Effective audibility.9.8.7.6.5..3.. 6 Sensation level (db) 6 8 m parameter.8.6.. 6 8 Hearing threshold (db HL) Frequency resolution AFRI (db) 6-35 Hz 6 8 Psychoacoustics Why measure only pure tone thresholds? Reason: OHCs lost AFRI (db) AFRI (db) AFRI (db) 6 khz - 6 8 6 khz - 6 8 6 khz - 6 8 Temporal resolution ATRI (db) 6 35 Hz Other measurements Reason: OHCs lost ATRI (db) ATRI (db) ATRI (db) - 6 8 6 khz - 6 8 6 khz - 6 8 6 khz - 6 8 Hearing threshold levels Outer hair cell function click-evoked otoacoustic emissions Frequency resolution psychophysical tuning curves cochlear dead regions TEN test Cognitive ability Age
Harvey Dillon Audiology NOW! Prescribing hearing aids for adults and children Healthy PTC no dead region Poor PTC: Dead region at khz Psychophysical tuning curve A9 Psychophysical tuning curve Masker Level (db SPL) 9 8 7 6 Signal Masker Masker Level (db SPL) 9 5 5 5 Masker Frequency (Hz) 8 3 5 Masker Frequency (Hz) Off-frequency listening: TEN test Off-frequency listening: PTC Basilar membrane vibration Threshold Equalizing Noise (TEN) Basilar membrane vibration Frequency or position Based on Moore () Frequency or position TEN and PTC (non) agreement khz PTC: Tip in place TEN: Alive 6 TEN: Dead TEN uncertain Can we better predict intelligibility if we use psychoacoustic results? PTC: Tip shifted 3 PTC uncertain
Harvey Dillon Audiology NOW! Prescribing hearing aids for adults and children Yes, a little speech deficit increases as frequency selectivity gets broader Likely intermediate effects Cognition Mechanical? PTC But not once we fully build HL into the SII prediction Age Cardiovascular Noise Stria OHC OAE TEN IHC HL Implications for prescription Pure tone thresholds critical Why are hearing thresholds so useful? Frequency selectivity Knowledge of temporal resolution, frequency resolution, dead regions adds relatively little to prediction of intelligibility Hearing thresholds Temporal resolution Speech Perception proficiency Age and cognitive ability affect all frequency bands similarly no effect on gain needed Age Central auditory processing Other Cognitive ability Gain; adults, medium input level (N = 87) Gain preference over time N = Source: Keidser, O Brien, Yeend, & McLelland (submitted)
Harvey Dillon Audiology NOW! Prescribing hearing aids for adults and children Adjustments to prescription to allow for experience Gain; adults, low and high input levels Gain adjustment 8 6 - - -6-8 New Experienced Experienced - New 6 8 Hearing threshold (db HL) Preferred gain deviation from NAL-NL re gain preferred at 65 db SPL in db.5.5 -.5 - -.5 - Smeds et al. 6 Zakis et al. 7 Suggest that the compression ratio should be slightly higher, at least for clients with 5 mild 8 and moderate hearing loss Input level in db SPL Compression ratio preferences: severe and profound hearing loss Average /CR in LF band...9.8.7.6.5..3. 5 5 55 6 65 7 75 8 85 9 Average HTL in LF band (db HL) Source: Keidser, Dillon, Dyrlund, Carter, and Hartley (7) :.8: 3: Binaural loudness correction 7 Gain variation (db) 6 5 3 6 8 Input level (db) RECD in infants (own mold; HA) 35 Directional microphones for infants and toddlers? 3 5 RECD_k 5 5-5.6.8.. 6. 8.. 6.. 8... Age (months) Teresa Ching Anna O Brien SNR improvement.9 Front Side Back NH.8 HI.7.6.5..3 -.. - SC SC SC3 SC. SC SC SC3 SC Scenario Scenario Yes! More to gain than there is to lose. Ching, O Brien et al, 9 db Proportion forward-looking
Harvey Dillon Audiology NOW! Prescribing hearing aids for adults and children Language at months after fitting Effect of age of fitting: p =.* Effect of hearing loss: p <.* Effect of prescription: p =.9 Covariate means: F6AV3FAMD: 55.6857 NAL EC-AC*"CatFit"*"CatPres"; LS Means EC-AC * CatFit: F(, 7 )=7.7, p=.5 Vertical bars denote.95 confidence intervals DSL EC-AC AP_EC EC-AC AP_AC Language skills at 3 yrs Effect of age of implant: p =. EC-AC*"CatCI"; LS Means Current effect: F(, 3)=.3, p=.8 "CatCI": F= 5.3, p =. EC-AC CA36P_EC EC-AC CA36P_AC PLS- Standard score (%) 9 8 PLS- Standard score (%) 8 6 7 (n = 55) (n = ) (n = 57) (n = ) < 6 mo >= 6 mo Fitting age category < 6 mo >= 6 mo Fitting age category < mo (n=9) >= mo (n=5) Implant age Consonant perception at 55, 7, 8 db Preference rating in real life Proportion correct..95.9.85.8.75 Consonant perception Current effect: F(, 9)=.955, p=.739 Vertical bars denote.95 confidence intervals NAL-NL DSL[i/o] 55 7 8 55 7 8 Level (db SPL) Level (db SPL) No of obs Preference rating - average of trials 3 and 8 SITE: Aus SITE: Can 6 8 6 7 8 dsl no pref nal Preference rating T Ching, NAL, CRC CI&HA INN 3 dsl no pref nal Empirical evidence: variations from NAL-NL Intelligibility in noise Wireless (e.g. FM) Directional microphones Intelligibility in quiet Amplification / tone controls Feedback cancelling Output level Children NAL-NL Adults Comfort & quality Convenience Adaptive noise suppression Multi-program Open fittings ADRO WDRC Autoprogram Bilateral manual control Phone interface Auto-telecoil Expansion Implantable hearing aids Rechargeable battery Bilateral feedback control Auto-gain Alerting tones and messages adaptation Active occlusion reduction Trainability Bilateral auto control Echo reduction Data logging Input level Integrated RECD Clinicians