A little history
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1. How loud is allowed? It’s déjà vu all over again! Ruth Bentler, Ph.D.
Dept of Speech Pathology & Audiology
The University of Iowa
3. Terms UCL
TD : my choice, because it isn’t always loudness the patient is reacting to; could be another dimension such as harshness, tinniness, annoyance, etc
4. Kochkin report (HJ, 2000) Only 44% were satisfied when asked about “comfort for loud sounds”
Of the 25 categories on the survey related to hearing aid performance and different listening environments, only two items received lower satisfaction rating: use in noisy situations, and listening in a large group
5. Can we rely upon manufacturers to get it right? We can’t rely upon them to agree! (more later)
6. Can we rely on formulas to get it right?
7. …more later on this topic…
8. Problems with inappropriately set output
9. …too high…
10. …or too low (reduced DR)
11. Measurement issues Test-retest reliability
Must use structured approach
Must average several runs
1 in 5 cannot do the task
What to do with the HL values when you get them?
12. Variability across hearing levels
13. Variability across gender, age
14. How does all this compare to the famous “Pascoe data”? Recall the graph…
Used in a number of manufacturer-based prescriptive formulas
Pascoe: For hearing levels of 20 to 60 dB HL, 2cc TDs range from 105 to 110 dB (or 10 dB higher than our large data set.
Pascoe used a protocol that pushed the TD upward.
15. Pascoe quote “Several ascending sequences are presented at each frequency, usually starting at progressively higher levels. This procedure forces the ‘thresholds of discomfort’ towards higher levels than initially chosen …is terminated when the discomfort judgment is not raised any further.” (page 132)
16. Pascoe data
17. Are these clinical measures valid? i.e, do they relate to real world loudness experiences?
Earlier Filion & Margolis data
Recent Munro & Patel data
Significant positive correlation between ratings (traffic, wind, eg) and difference between RESR and measured TDs
No such relationship for short duration sounds (cutlery, door slamming, eg)
18. What about in situ measures of TD? i.e., using the patient’s own hearing aid as the sound generator
Ben Hornsby (Vanderbilt) found that in situ measures agreed quite well with manufacturer recommended OSLP, but varied by as much as 17 dB for the same loss!
19. Loudness Summation For years we have believed that TDs for HI are higher than those of NH
May apply to pure tone stimuli, which is not real-world!
Due to loudness summation being greater in HI than NH, evidence of TDs for complex sounds being lower for HI than NH
20. Binaural Summation Seems to depend upon the level of input, ranging from 3 dB at threshold to 6 dB at moderate or higher level inputs
Seems to encourage the use of binaural correction for fitting hearing aids
21. Power (or channel) summation The sum of the outputs from independent channels must be considered
e.g., adding dBs for equal or unequal inputs
e.g, two independent channels of 110 dB output will equal 113 dB output
e.g., four independent channels of 110 dB output will equal 116 dB ouput
IF all channels outputting level simultaneously!
22. Power (channel) summation, cont. Bentler & Pavlovic derived regression equation for loudness plus power summation:
Reduction = 3.95 + 12.88log(n), where n equals number of channels
5 dB for 2 channels
9 dB for 4 channels
23. Why not just predict? NAL efforts
OSPL3FA = .3T3FA +88.9 dBSPL (<60 HL)
OSPL3FA = .54T3FA +74.3 dBSPL (>60 HL)
Where T is threshold in HL
Results in placement of maximum output ½ way between data of LDL and level that will saturate speech signal
24. What about prediction?
25. Bentler and Cooley (2001, Ear & Hearing) For hearing levels below 60 dB only 1% of the variance was accounted for by HL
For hearing levels above 60 dB, 11% of the variance accounted for by HL
TDs equivalent to CONTOUR results in high frequencies only
26. Children? No reason to believe their TDs are different than those of adults
Can reliably test children over the age of 7 or 8 MA
May need alternate approach (cross-modality matching, sad faces, etc)
27. What about mixed loss? Not a lot of research in this realm, but Harvey Dillon’s suggestion of .875 the air/bone gap sounds reasonable!
28. Clinical procedure Several frequencies in ascending approach (750 Hz and 3000 Hz best predictors of TD for complex sounds)
Convert to 2cc values
Consider binaural summation (5dB?)
Consider power (channel) summation (5 dB for 2 CH; 9 dB for 4 CH)
Real life obnoxious sounds!
Follow-up APHAB, IOI-HA etc
29. RETSPLs Determine own
500 13.5 500 8.5
750 8.5 750 5.0
1000 7.5 1000 3.5
2000 11 2000 6.5
3000 9.5 3000 5.5
4000 10.5 4000 1.5
30. Final Words Don’t count on the subject to acclimate/adjust to excessive output
Ask for precise situations of discomfort in follow up appointments