Frequency Transposition

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1. Frequency Transposition in hearing aids for school-age children Jenny Smith 1,2 ,Marilyn Dann 1 and Margaret Brown 1 1 Deafness Studies Program, Graduate School of…
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  • 1. Frequency Transposition in hearing aids for school-age children Jenny Smith 1,2 ,Marilyn Dann 1 and Margaret Brown 1 1 Deafness Studies Program, Graduate School of Education, University of Melbourne, Australia. 2 Jenny Smith, Audiological Consultancy, South Yarra, Australia Contact: jensmi@ozemail.com.au
  • 2. Basic Principles <ul><li>All children need to access the high frequency fricatives, such as /s/, /t/ which are critical in spoken English </li></ul><ul><li>Children with severe /profound high frequency loss have greater difficulties accessing these speech cues. </li></ul><ul><li>“ Dead regions” (> 75dB) do not hear, regardless of gain </li></ul><ul><li>Frequency transposition is an alternative way of accessing high frequency cues and has relevance for children due to their greater neural plasticity. </li></ul>
  • 3. The Sounds of Speech <ul><li>Hearing –impaired children need to access the high frequency fricatives which are critical in spoken English </li></ul><ul><ul><li>/s/ and /z/ mark plurals (cat, cats), possession (John’s book) , contractions (it’s, that’s), and the third person singular tense (he goes, he gets) (Plant, 2007) </li></ul></ul><ul><ul><li>/s/ and /t/ are two of the most commonly occurring consonants in casual speech ( Mines, 1978). </li></ul></ul><ul><li>Children with severe /profound high frequency loss have greater difficulties accessing these speech cues. </li></ul>
  • 4. Spoken English <ul><li>Speech analysis has shown that recognition of fricatives is reached at a bandwidth of 4-5KHz for males but not until 9KHz for female and child talkers (Plant, 2007). </li></ul><ul><li>A recent review of hearing aid studies concludes: </li></ul><ul><ul><li>that results for adults cannot predict speech and language performance in children </li></ul></ul><ul><ul><li>the bandwidth of current aids is inadequate to represent the high-frequency sounds of speech, particularly female speakers (Stelmachowicz et al ,2004) </li></ul></ul><ul><ul><li>Epoq by Oticon now has a 10KHz bandwidth </li></ul></ul>
  • 5. Accessing Speech <ul><li>High frequency hearing loss, (HTL> 75dB) , is typically associated with a “dead region of the cochlea”, a complete loss of inner hair cell and/or neural function over the basal region of the cochlea ( Moore, 2004). </li></ul><ul><li>If there is no mechanism to transmit the amplified signal to the brain, the user cannot access the information, regardless of the hearing aid bandwidth. </li></ul><ul><li>However if there is a dead region of the cochlea, frequency discrimination can be re-learnt. (Moore, 2000) </li></ul>
  • 6. Frequency Transposition <ul><li>Frequency transposition offers an alternative way of accessing high frequency speech. </li></ul><ul><li>This technology which aims to provide audibility for the “unaidable” high frequency sounds by changing them into an audible lower frequency substitute. (Kuk, 2006) </li></ul><ul><li>Children are an ideal client group for this technology because they have greater neural plasticity and more potential to use a newly accessible signal (Gabriel et al, 2006). </li></ul>
  • 7. What are the problems ? <ul><li>In the past, frequency transposition has not been very successful due to : </li></ul><ul><ul><li>Technical limitations of the signal processing which produce processing artefacts </li></ul></ul><ul><ul><li>Very different types of transposition frequency maps </li></ul></ul><ul><ul><li>Different fitting strategies regarding the degree of transposition </li></ul></ul><ul><ul><li>Different target audiograms, ski-slope , corner, or U-shaped </li></ul></ul><ul><ul><li>Time allowed to make use of altered cues </li></ul></ul><ul><ul><li>The amount of training provided to the user </li></ul></ul><ul><li>( Dillon, 2007, pers.comm) </li></ul><ul><li>Can new DSP aids help overcome the limitations ? </li></ul>
  • 8. The project <ul><li>Evaluate linear frequency transposition </li></ul><ul><ul><li>Verify the degree of transposition using REM </li></ul></ul><ul><li>Evaluate with ski-slope losses </li></ul><ul><li>Evaluate in schools with facilities for training </li></ul><ul><ul><li>Measure over time to allow for adaptation </li></ul></ul><ul><li>But first, find the subjects ! </li></ul><ul><ul><li>I approached 11 schools to find 6 children </li></ul></ul>
  • 9. Widex Inteo Frequency Transposition <ul><li>Inteo offers true linear transposition, which preserves the temporal structure of the signal so it is easily recognised </li></ul>Can hearing impaired children benefit from this technology ?
  • 10. Identifying Candidates <ul><li>In Victoria , a region of 5 million people there are 579 children aged 8-13 yrs with permanent hearing loss : </li></ul><ul><ul><li>436 children have a mild/moderate loss (31-60dB) </li></ul></ul><ul><ul><li>143 children have severe/ profound loss (61 -90dB) </li></ul></ul><ul><ul><li>there is no data on slope of loss in Australia </li></ul></ul><ul><ul><li>ski-slope loss : Colorado : 5 out of 215 , Mid-west : 4% </li></ul></ul><ul><li>The reported need for training as a variable suggested a supported educational setting was desirable </li></ul><ul><li>I approached 11 schools with hearing facilities : </li></ul><ul><ul><li>3 with mild/moderate 3FHL and 3 with severe/profound 3FHL </li></ul></ul>
  • 12. History <ul><li>Key goals: </li></ul><ul><ul><li>To optimize the use of good low frequency hearing </li></ul></ul><ul><ul><li>To provide high frequency access by frequency transposition, AE </li></ul></ul><ul><ul><li>To improve cosmetic appeal and hearing aid usage </li></ul></ul><ul><li>Boy, aged 14.4 years </li></ul><ul><li>Hearing loss caused by lack of oxygen at birth </li></ul><ul><li>Hearing aids fitted under 12 mths </li></ul><ul><li>Always a reluctant aid user </li></ul><ul><li>Attending mainstream school, with minimal educational support </li></ul>
  • 13. Widex Inteo IN9-AE elan flex aids <ul><li>IN9 fitted using basic protocol </li></ul><ul><ul><li>Sensogram and feedback test </li></ul></ul><ul><ul><li>3 weeks acclimatisation </li></ul></ul><ul><ul><li>Positive response </li></ul></ul><ul><li>Introducing Frequency transposition </li></ul><ul><ul><li>Audibility Extender (A E) set as first program, P1 </li></ul></ul><ul><ul><li>P2 (master) and VC options provided </li></ul></ul><ul><ul><li>Start freq = 2000Hz, Expanded, Gain= +10dB </li></ul></ul><ul><li>Reviewing Frequency transposition </li></ul><ul><ul><li>rejected by subject as too confusing, echoic, slushy </li></ul></ul><ul><ul><li>Counsel about options, review again, check data log </li></ul></ul><ul><ul><li>Evaluated using live speech mapping </li></ul></ul>
  • 14. Setting AE Turquoise AE=2000 E Purple AE= 2000 B Green AE=2500 B Blue AE=3200 B
  • 15. Verifying the Fitting VC = maximum
  • 16. Evaluating Aid Benefit Test Parameter Parent/student Questions and interviews Changes in overall hearing Teacher /student LIFE Changes in classroom listening Recorded speech sampling Speech Production Goldman-Fristoe Test of Articulation Speech Articulation CNC words and phonemes Speech Perception
  • 17. Speech Perception Testing <ul><li>Presentation </li></ul><ul><ul><li>Tested with Consonant-Nucleus-Consonant (CNC) monosyllabic word lists </li></ul></ul><ul><ul><li>Live voice presentation at normal speech levels at 1 m. in a quiet room </li></ul></ul><ul><ul><li>Tested pre-fitting, at fitting and post -fitting every 6 weeks for 24 weeks. </li></ul></ul><ul><li>Protocol </li></ul><ul><ul><li>Two lists presented with AE-ON and two lists with AE-OFF </li></ul></ul><ul><ul><li>One list given audio-visually and one audition alone, for each setting </li></ul></ul><ul><ul><li>Responses for words and phonemes scored live and recorded on video </li></ul></ul><ul><li>Responses </li></ul><ul><ul><li>Scored by two experienced transcribers with normal hearing </li></ul></ul><ul><ul><li>Scored by a third experienced transcriber if these scores varied by >8%. </li></ul></ul><ul><ul><li>Mean of the two closest scores used for further data analysis. </li></ul></ul>
  • 18. Speech Perception : CNC words Significantly better scores recorded 6 weeks post-fit and sustained over time
  • 19. Speech Production: G-F 2 Test Substitution : initial /z/ with /d/, Omission: final /v/ Lateralised: initial /dz/ Substitution: final /f/ with /s/ Omission: Final /d/ Slushiness greatly reduced Says himself with AE off he cannot hear /s/ 90 Post Fit Omission: final /dz/, /v/, /s/, /z/ Lateralised: initial /s/ Omission: final /s/ Substitution: kl with kr sp with /b/ Omission: initial /g/ final /p/; substitution: medial /v/ with /b/; weak /r/ Slushy quality Lateral /s/ 54 Pre-Fit Fricatives sentences Fricatives In words Consonant clusters Single consonant Over-all production G-F Score
  • 20. Speech Production: G-F 2 Test 90 Post-Fit 54 Pre-Fit
  • 21. Spoken English <ul><li>Spectrographic Analysis: Plant, 2007 </li></ul>
  • 22. Classroom listening: LIFE +35 +17 0 -17 -35 LIFE Student Response LIFE Teachers Response +35 = Strong support for positive change: use is highly beneficial 12 weeks post FT introduction 81.6 (+ 18.3%) 86.6 63.3 IN9-AE % 12 wks post -fit IN9 –M % 3wks post-fit Pre-Fit %
  • 23. Described benefit Not really, he’s a teenager One at a time is OK Participating more in family discussions Most definitely I hear the whole sentence Responding better in 1:1 conversations Not that I have observed I heard the birds Hearing high soft environmental sounds Definitely hearing car indicators and gears I hear the phone ring and the kettle boil Hearing new sounds These aids are working wonders for him I am hearing, not deaf Overall comment Much clearer, even his grandfather commented Sounds different Changes in own speech Sometimes Same as old aids Understanding unknown speakers Parent Student
  • 24. Hearing Aid Outcomes <ul><li>Child 1: Extreme ski-slope hearing loss </li></ul><ul><ul><li>Increased willingness to wear hearing aids </li></ul></ul><ul><ul><li>Significant sustained improvements in speech perception and speech production </li></ul></ul><ul><ul><li>Improved listening skills in the classroom and at home </li></ul></ul><ul><ul><li>Significant changes in confidence, self esteem and self-image </li></ul></ul><ul><ul><li>“ These aids are working wonders for him” </li></ul></ul>
  • 26. History <ul><li>9.6 year old girl </li></ul><ul><li>Serious medical condition needing extended hospitalization with hearing loss reported to be due to ototoxic drugs (gentamyacin) </li></ul><ul><li>Fluctuating conductive overlay </li></ul><ul><li>Attends mainstream school with oral and signing support but struggles to access the curriculum </li></ul>Figure 1:Unaided audiogram
  • 27. W IDEX Inteo IN19 + Audibility Extender (AE) <ul><li>IN19 fitted using basic protocol </li></ul><ul><ul><li>Sensogram and Feedback test </li></ul></ul><ul><ul><li>3 weeks acclimatisation </li></ul></ul><ul><li>Introduce Frequency transposition </li></ul><ul><ul><li>Audibility Extender (AE) set as first program, P1 </li></ul></ul><ul><ul><li>Master program and volume control deactivated </li></ul></ul><ul><ul><li>Start frequency = 2500Hz, Expanded, Gain= +10dB </li></ul></ul><ul><ul><li>Identification LING 7 sounds confirmed access to /s/, /sh/ </li></ul></ul><ul><li>On review: no adjustments indicated </li></ul>
  • 28. Verifying the Fitting
  • 29. Speech Perception : CNC words Significantly better scores with frequency transposition (AE-ON) over time Middle ear infection and school holidays linked to poorer scores at 12-18wks
  • 30. Speech Production <ul><li>16 new words </li></ul>SWAT Test 108 Single Words (Paatsch,1997) G-F 2 Test Improved production consonant clusters /fr/ /kr/ /kw/ 79.6% 18 wks Post-fit 14.8% Benefit 64.8% Pre-fit 78 24 wks Post- Fit 78 Pre-Fit
  • 31. Spoken English <ul><ul><li>Pre-Fit </li></ul></ul>Post- Fit
  • 32. Classroom Listening: LIFE <ul><li>Student Response </li></ul><ul><li>Teacher Response </li></ul><ul><li>TOD reported positive changes in speech and listening. </li></ul><ul><li>Classroom teacher did not report benefit but this may reflect poor academic progress. </li></ul>Teacher: “She is more aware, more on task, more tuned in” 75 % IN19-AE 24 wks post AE 76.3 % (+23.6%) IN19-AE 12 wks post AE 63.6% 52.7% IN19–M 3 wks post-fit Pre-Fit
  • 33. Data Logging Interpretation
  • 34. Hearing Aid Outcomes <ul><li>Child 2: Severe hearing loss </li></ul><ul><ul><li>Improvements in speech perception </li></ul></ul><ul><ul><li>Measured changes in speech production of isolated words </li></ul></ul><ul><ul><li>Perceived improvement in listening and auditory awareness </li></ul></ul><ul><li>“ She is more aware, more on task, more tuned in” </li></ul>
  • 36. <ul><li>15.5 year old girl </li></ul><ul><li>Congenital hearing loss </li></ul><ul><li>Good oral communicator </li></ul><ul><li>Age at first fitting: 19mths </li></ul><ul><li>Left cochlear implant: 4.8yrs </li></ul><ul><li>Always worn bimodal aid </li></ul><ul><li>Considering bilateral cochlear implants </li></ul><ul><li>Frequency transposition aid trialed as an alternative </li></ul>History Unaided right hearing levels, No measurable left hearing
  • 37. W IDEX Inteo IN19 + Audibility Extender (AE) <ul><li>IN19 fitted using basic protocol </li></ul><ul><ul><li>Sensogram and Feedback test </li></ul></ul><ul><ul><li>Immediate introduction of AE </li></ul></ul><ul><li>Frequency transposition settings </li></ul><ul><ul><li>Audibility Extender (AE) set as first program, P1 </li></ul></ul><ul><ul><li>Master program and volume control active </li></ul></ul><ul><ul><li>Start frequency = 2500Hz, Expanded, Gain= +14dB </li></ul></ul><ul><li>On review: rapid acclimatisation, no adjustments needed </li></ul><ul><ul><li>She did not use either P1 or volume control </li></ul></ul>
  • 38. Verifying the Fitting
  • 39. Speech Perception <ul><li>Aid scores show the added benefit provided to the CI </li></ul><ul><li>Audition alone scores show the importance of visual cues </li></ul>Results show a synergy for CI + aid + lip-reading. 86 40 46 BKB Sentence% CNC Phoneme% CNC Word % 19.3 93.3 62 68 CI+IN19-AE Audition only CI+ IN19-AE Audio-visual Triano SP Audio-visual IN19-AE Audio-visual 6 86 28 34
  • 41. Mother <ul><li>Her initial comment was “I can not only hear you, but I can understand what you’re saying” which was amazing. </li></ul><ul><li>My daughter says “ both the ears are now listening at approximately the same level, rather than having the cochlear implant listening level high and the hearing aid level low. Both the ears are getting a similar input ” </li></ul><ul><li>“ I was behind her and she was reading a book with only the new hearing aid on ( no CI) and we had a short conversation. It was amazing she could have a proper conversation without lipreading” </li></ul><ul><li>There are lots of differences in her sentence structure – she is starting to use final consonants better and her past tense has improved, she is putting on /t/ and /d/ , and she now says “women” not “womans” </li></ul><ul><li>The teachers at school asked if she had got a new hearing aid over the holidays as her speech was a lot clearer and she was listening better. </li></ul><ul><li>I didn’t think the improvement would be as good as it was. It is not so urgent to get a (second) cochlear implant now. </li></ul>
  • 42. Figure 1.1 Similarity of the two vowels oo and ee when the second formant is inaudible because of hearing loss ( grey area). Sound level ee 250 1000 4000 Frequency (Hz) 500 2000 oo First formant Second formant Source: Dillon (2001): Hearing Aids Audibility of formants
  • 44. Hearing Aid Outcomes <ul><li>Child 3: Bimodal fitting for a profound loss </li></ul><ul><ul><li>A synergy can
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