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Does Higher Technology Result in Higher Levels of Benefit?. BCASLPA October 22, 2004 Ruth Bentler www.shc.uiowa.edu. What features?. Dsp versus Analog Directional Mics Noise Reduction Feedback Cancellation. Dsp versus Analog. Orange Juice or Tomato Juice

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Does Higher Technology Result in Higher Levels of Benefit?


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    1. Does Higher Technology Result in Higher Levels of Benefit? BCASLPA October 22, 2004 Ruth Bentler www.shc.uiowa.edu

    2. What features? • Dsp versus Analog • Directional Mics • Noise Reduction • Feedback Cancellation

    3. Dsp versus Analog • Orange Juice or Tomato Juice • Cardiovascular or Weight-Bearing • Puppy or cable

    4. Dsp versus Analog • Orange Juice or Tomato Juice • Cardiovascular or Weight-Bearing • Puppy or cable

    5. Digital versus analog • Not a debate amongst (most) researchers • Easy to contrive the design • Often misleads the clinician • E.G. • Wood & Lutman (March 2004, IJA)

    6. Abstract • Question: Are dsp hearing aids better than analog (linear) hearing aids? • Design: 100 first-time users, single- blinded, wore the HAs for 5 weeks each • APHAB, GHABP, QoL, Diary • REAR, Speech-in-Noise • Results…

    7. Results • Better dsp performance at 75 dB inputs (4%); no difference at 65 dB input • No difference in QoL • No difference in use time • No difference in APHAB subscales (n=36) • Difference in Satisfaction subscale of GHABP in favor of dsp • 60 preferred dsp; 31 preferred analog

    8. Conclusions • “Dsp provides significantly better speech recognition performance for raised speech in background noise than carefully fitted (“but not adjusted”) linear analog hearing aids.” • “Users report somewhat greater satisfaction…and less aversiveness to sound.

    9. An indepth look at the facts… • Gain/output not controlled (audibility??) • Limiting versus peak clipping not controlled (distortion??) • Linear aids not adjusted to “comfort”, as were dsp aids (blinded??) • And, finally, features such as directional mics, noise reduction and feedback cancellation were active in the dsp circuits…

    10. So, one more time… • The advantages of dsp hearing aids (to the end user) lie in the features, if they lie at all… • Manufacturer benefits? • Dispenser benefits?

    11. Directional Microphones?

    12. What we know… • One and two mic designs • Low frequency compensation • Mic noise goes up (and up) • Many companies use mic noise algorithm

    13. Quick Tutorial • Ways to build directivity into a hearing aid case: • Single mic with two ports • Two omni mics • Combination of omni & directional mics • Three mics • Mic array

    14. Directional Microphone

    15. Reading a Polar Plot

    16. OmniDirectional Microphone Polar plot for omnidirectional mic in free field Level of signal Angle of signal source

    17. Polar Response Pattern Free field characteristics of different types of microphones (Knowles TB 21) Omnidirectional Cardioid Hypercardioid Supercardioid

    18. Dittberner, 2003

    19. Dittberner, 2003

    20. Head/pinna/torso effect

    21. Head/pinna/torso effect

    22. Wouters, 2003

    23. Wouters, 2003

    24. Quick tutorial, cont. • Ways to implement directionality in the hearing aid case: • Fixed polar pattern • Program different polar patterns in different memories • Automatic directional mode • Adaptive directional mode

    25. 80 70 60 50 40 30 20 10 0 -10 100Hz 200 500 1kHz 2 5 10kHz Ways to quantify directivity • Front-to-back ratio (FBR) • Directivity Index (DI) • Theoretical • Free field • KEMAR Frequency, Hz

    26. Directivity Index (DI)

    27. 4.8 4.0 2.3 6.0 5.1 3.0 5.7 5.0 3.3 FF (BTE) KEMAR (BTE) Theoretical Cardioid Hypercardioid Supercardioid

    28. 4.8 4.1 2.7 6.0 5.6 3.3 5.7 5.4 3.5 FF (ITE) KEMAR (ITE) Theoretical Cardioid Hypercardioid Supercardioid

    29. Laboratory Data • We have 30-40 years of lab data and trade-magazine evidence that • Directional mics can improve SNR • That enhancement is based on • # and placement of speakers • Type/level/distance of noise • Reverberation • Baseline comparison (unaided, BTE/ITE, Omni) • LF Compensation versus hearing levels

    30. Laboratory Data • AND, that lab data do not relate very well to self-report data • E.g., Walden, Surr & Cord (Hearing Journal, 2003)…

    31. Walden, Surr, & Cord, 2003

    32. Laboratory Data • And, we can’t predict directional advantage: • Ricketts & Mueller (JAAA, 2000) examined three studies for effect on directional advantage: • Slope of hearing loss • Amount of high frequency hearing loss • Aided omnidirectional advantage • In one study, found significant negative relationship between aided omnidirectional performance and directional advantage

    33. Cord, Surr, Walden & Olsen (2002) Performance of directional microphone hearing aids in everyday life, JAAA, 295-307. • Called back users of directional mic hearing aids that fell into two groups • Those who used them regularly (deemed successful)(n=22) • Those who did not, and used the default omnidirectional mode (deemed unsuccessful)(n=26) • No predictive power in APHAB scores

    34. Cord, Surr, Walden & Olsen (2002) • Microphone Performance Questionnaire (MPQ) indicated directional mics preferred when signal is in front (near) and noise is in back • All 48 participants reported being satisfied with their HAs in each mic configuration; although the directional mic used less often, equally satisfied with it when they did...

    35. Walden and Walden (2004). Predicting success with hearing aids in everyday living, JAAA, 342-353. • Purpose of the study: Investigate relationship between two measures of hearing aid success (IOI-HA and HAUS) and demographic and audiometric measures. • No blinding; clinic appointment data (n=50) • Not really a comparison of mic conditions, although • IOI-HA showed statistically significant difference across the groups • Omni only (n=29) • Omni/Directional with a switch (n=21) • NO difference in HAUS across two groups

    36. Walden, Surr, Cord, and Dyrland (2004). Predicting hearing aid microphone preference in everyday listening. JAAA, 365-396. • Purpose of the study: Define environments for which either the omnidirectional or directional mode was better (thus providing guidance): • Talker location • Noise location • Distance • Time • Ease of listening • (Indirectly assigned reverberation)

    37. Cord, Surr, Walden & Dyrland (2004) • Beginning of a model! • Mean estimated use time was 61.8% for omni mode and 38.2% for directional mode. • Average use of the omni mode was 65% for 8 participants for whom the default setting was omni, and 58.9% for the 9 participants for whom the default was directional.

    38. Thus, the question of importance (to me!)

    39. Do experienced/trained users of hearing aids with directional microphones report better amplification outcomes in daily life than users of hearing aids without directional microphones?

    40. (Infamous) Valente, Fabry & Potts (1995).Recognition of speech in noise with hearing aids using dual microphones, JAAA, 440-449. • Purpose: To determine the effectiveness of a directional mic (two omni design) • Two sites (25 at each) • No blinding • Although not a comparison to omni design, PHAB (Site 1) and APHAB (Site 2) showed subjects performing above the mean benefit norms.

    41. Preves, Sammeth, & Wynne (1999). Field trial evaluations of a switched directional/omnidirectional ITE hearing instrument (1999). JAAA, 273-284. • Purpose: To evaluate the usefulness of a switch-option directional microphone system • 10 blinded subjects (single-blinded cross-over design) wore aids for 2 trials • Self-report inventories (after non-equalized trial and equalized trial) • APHAB • Subjective Comments

    42. Preves, Sammeth, & Wynne, continued • For Trial #1 (non-equalized) • APHAB: RV subscale showed directional mode significantly better (fewer reported problems) • Comments: If only one, 6/10 directional mode; Subjects “hesitant to give up” either mode • For Trial #2 (equalized) • APHAB: RV and BN RV subscale showed directional mode significantly better (fewer reported problems) • Comments: If only one, 6/10 directional mode; Subjects “hesitant to give up” either mode

    43. Boymans and Dreschler (2000), Field trials using a digital hearing aid with active noise reduction and dual-microphone directionality, IJA, 260-268. • 16 subjects (single-blinded cross-over design) wore aids for four consecutive field trials • No noise reduction • Directional mics only • Noise reduction only • Directional mics plus noise reduction

    44. Boymans and Dreschler (2000) continued • “Subjective” outcome measures • Paired comparisons (only in the lab) • APHAB