Presentation on theme: "How loud is allowed? Its déjà vu all over again! Ruth Bentler, Ph.D. Dept of Speech Pathology & Audiology The University of Iowa"— Presentation transcript:
How loud is allowed? Its déjà vu all over again! Ruth Bentler, Ph.D. Dept of Speech Pathology & Audiology The University of Iowa
A little history… Clinical effort s 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 isnt 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 cant 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
…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)
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 patients 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 = log(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 OSPL 3FA =.3T 3FA dBSPL (<60 HL) OSPL 3FA =.54T 3FA 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 Dillons 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 6cc2cc
Final Words Dont count on the subject to acclimate/adjust to excessive output Ask for precise situations of discomfort in follow up appointments