How loud is allowed?It’s déjà vu all over again!

Ruth Bentler, Ph.D.Dept of Speech Pathology & AudiologyThe University of Iowaruth-bentler@uiowa.edu

A little history…

Clinical effort 1973-1980s Dissertation topic, 1987 Bentler & Pavlovic, 1988 Bentler, Abbas, and Pavlovic, 1990 Gad & Bentler, 1993 Ricketts & Bentler, 1994 Bentler & Cooley, 2001 Bentler & Nelson, 2001 Warner & Bentler, 2002

Terms

UCL ULC LDL TD : my choice, because it isn’t

always loudness the patient is reacting to; could be another dimension such as harshness, tinniness, annoyance, etc

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

Can we rely upon manufacturers to get it right?

We can’t rely upon them to agree! (more later)

Can we rely on formulas to get it right?

…more later on this topic…

Problems with inappropriately set output

…too high…

…or too low (reduced DR)

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?

Variability across hearing levels

Variability across gender, age

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.

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)

Pascoe data

Are these clinical measures valid?

i.e, do they relate to real world loudness experiences?

Probably 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)

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!

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

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

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! Several suggestions:

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 Dillon suggestion:

5 dB for 2 channels 9 dB for 4 channels

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

What about prediction?

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

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)

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!

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) RESR Real life obnoxious sounds! Follow-up APHAB, IOI-HA etc

RETSPLs

Determine own 6cc 2cc

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

Final Words

Don’t count on the subject to acclimate/adjust to excessive output

Ask for precise situations of discomfort in follow up appointments

Questions?