Comparison of performance with hearing aid programmed to NAL-NL1 first-fit and optimized-fit.
Sreena Ediyarath Narayanan, Puttabasappa Manjula
PMID 34669764WHAT IT FOUND
Optimizing a hearing aid to NAL-NL1 targets with probe-microphone verification improved soft-sound audibility by 10 dB and raised Kannada word scores by 7% versus manufacturer first-fit in 11 adults.
Key findings
01The hearing aid programmed to match NAL-NL1 targets gave significantly more real-ear gain than the manufacturer first-fit, especially at high frequencies.
02Aided thresholds were 10 dB better on average with optimized-fit, and the articulation index rose from 0.4173 to 0.7009, both differences statistically significant.
03Word recognition in quiet was 7% higher with optimized-fit than first-fit on a 25-word test, a significant difference.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
Only 11 adults were tested, and all had moderate to moderately severe sensorineural hearing loss, so the result may not apply to other degrees or configurations of hearing loss. The study used one 16-channel behind-the-ear hearing aid model from one manufacturer, so other default first-fit settings may behave differently. Only speech recognition in quiet was tested, not speech in noise, and noise reduction and directional microphone were switched off. No subjective satisfaction, long-term use, acclimatization, or real-world outcomes were measured. Aided thresholds and articulation index are indirect audibility measures, and the paper states speech recognition cannot be directly inferred from aided thresholds. The study tested only NAL-NL1, not NAL-NL2 or other generic formulae.
The easy way to misread this
Do not read the 7% word recognition gain as proof that optimized-fit works in daily life. The study measured laboratory performance in 11 adults with one hearing aid model and only speech in quiet.