Question
Data show that by using the manufacturers’ proprietary ‘first fit’ hearing aid programming settings, we may be fitting hearing aids 10 dB or more below the true NAL-NL2 prescriptive targets. Does it really matter where we start if we are performing validation anyway - wouldn’t this be quickly apparent, especially if we are conducting speech perception measures?
Answer
Gus Mueller: This is assuming all people fitting hearing aids are conducting validation, and are doing are doing some time of word recognition testing. Even if you are, whether or not it becomes apparent that the hearing aids are significantly underfit would depend upon the presentation level for this testing. If you were to deliver speech at 65 dB SPL or so, it may not be apparent that the hearing aids are underfit, especially if the patient only has a mild-to-moderate loss. If you were delivering speech at 50 – 55 dB SPL, then yes, it probably would be apparent.
But here is another consideration. Let’s say you fit your patient “Bob”, with hearing aids programmed to the manufacturer’s first fit settings. Next, you perform the QuickSIN and find that Bob has an SNR loss of 8 dB. Had you fit the hearing aids correctly (i.e. verified to a prescriptive target like NAL) maybe the SNR loss would only be 4 dB. But how would have you known that the 8 dB SNR loss is not Bob’s max score for the QuickSIN? One of the problems of using word recognition testing for hearing aid validation is that unless you conduct testing at a lot of different hearing aid settings—more than anyone would ever do in a clinical setting--it is very difficult to determine when the patient is performing to their maximum. You might conder their performance as “expected” or “good enough”, even when there is room for improvement. This is why I believe the starting point in fitting hearing aids should always be to set the output in the ear canal to validated prescriptive targets, and then proceed with validation to support your verification. That is my take on it. Todd, what is your opinion?
Todd Ricketts: I would agree. I think the biggest concern and the biggest issue with just going with the manufacturer’s first fit, even if you show benefit by using a low level speech stimulus in your validation, is that you really do not know whether the patient could have done even better. It would only show up if you did a comparison of both fittings.
Gus Mueller: Actually Todd, in 2012 there was an article in Hearing Review that looked at that very thing. Leavitt and Flexer compared manufacturer first fit for the premier hearing aid for the six major manufacturers to a verified NAL fitting for the same products (Leavitt and Flexer, 2012). Using the QuickSIN, they found that there were SNR improvements of something like 6 to 10 dB when the hearing aids were programmed to the NAL versus the manufacturers’ proprietary first fit. This is a very important topic when we are talking about fitting people with new hearing aids, but then neglecting to provide them the necessary amplification to understand speech in background noise.
References
Leavitt, R.J., & Flexer, C. (2012, December). The importance of audibility in successful amplification of hearing loss. Hearing Review. Retrieved from https://www.hearingreview.com/
Editor’s note: This Ask the Expert was adapted from the webinar, Vanderbilt’s Audiology Journal Club: Hearing Aid Features and Benefits – Research Evidence. To view the course in its entirety, register here.
