The Effect of Hearing Aids on Sound Localization in Mild Unilateral Conductive Hearing Loss.

Background:  Binaural hearing is of utmost importance for communicating in noisy surroundings and localizing the direction of sound. Unilateral hearing loss (UHL) affects the quality of life in both childhood and adulthood, speech development, and academic achievements. Sound amplification using air-conducting hearing aids (HAs) is a common option for hearing rehabilitation of UHL. The processing time of digital HAs can significantly delay the acoustic stimulation in 3 to 10 milliseconds, which is far longer than the maximal natural interaural time difference (ITD) of 750 microseconds. This can further impair spatial localization in these patients.

Purpose:  We sought to assess whether HA effects on ITD and interaural level difference (ILD) impair localization among subjects with unilateral conductive hearing loss (UCHL).

Research Design:  "Normal"-hearing participants underwent localization testing in different free field settings.

Study Sample:  Ten volunteers with "normal"-hearing thresholds participated.

Intervention:  Repeated assessments were compared between "normal" (binaural) hearing, UCHL induced by insertion of an inactivated HA to the ear canal (conductive HL), and amplification with a HA.

Results:  In UCHL mode, with HA switched-off, localization was significantly impaired compared to "normal" hearing (NH; η= 0.151). Localization error was more pronounced when sound was presented from the front and from the side of the occluded ear. When switched-on, amplification with HAs significantly improved localization for all participants compared to UCHL. Better localization with HAs was seen in high frequencies compared to low frequencies (η= 0.08, 0.03). Even with HAs, localization did not reach that of NH (η= 0.034).

Conclusion:  Mild UCHL caused localization to deteriorate. HAs significantly improved sound localization, albeit the delay caused by the device processing time. Most of the improvements were seen in high-frequency sounds, representing a beneficial effect of amplification on ILD. Our results have potential clinical value in situations of mild CHL, for instance, otitis media with effusion.