Sound Externalization: A Review of Recent Research.
Virginia Best, Robert Baumgartner, Mathieu Lavandier and 2 others
PMID 32914708WHAT IT FOUND
Hearing aids often make sounds feel inside the head because they block the ear or distort timing and level cues between the ears.
This review explains why that happens and notes that patients may adapt over time, but rigorous evidence on how to fix it is still missing.
Key findings
01Hearing aid users report lower externalization scores than unaided listeners, with bilateral fittings scoring lower than unilateral ones.
02Fast-acting compression in hearing aids reduces externalization by distorting interaural level differences, creating a conflict with timing cues.
03There are no rigorous studies comparing externalization across different earmold fittings, despite anecdotal reports that open molds help.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
This is a narrative review, not a systematic review or meta-analysis, so it may not capture all relevant studies or weigh them equally. The review highlights a scarcity of empirical data on hearing aid externalization, noting that many claims are based on anecdotal reports or small studies. There are no rigorous studies comparing different earmold fittings for their effect on externalization. The mechanisms behind adaptation to hearing aid distortions are not fully understood.
Declared interests
The authors declare no conflicts of interest. The work was supported by various national and international funding bodies including the National Institute on Deafness and Other Communication Disorders.
The easy way to misread this
Do not assume that hearing aid internalization is a permanent problem or that switching to open earmolds is a proven solution. The review states there are no rigorous studies on earmold effects, and many negative spatial effects may decline as listeners acclimatize to the altered cues.