Impact of hearing impairment in unilateral hearing loss: A multicenter study of standardized sound localization tests in Japan.

OBJECTIVE

This study had two primary objectives: first, to standardize a sound localization test across multiple facilities in Japan, and second, to use this standardized test to analyze sound localization ability in patients with unilateral hearing loss (UHL) and identify related clinical and demographic factors.

METHODS

Sound localization tests were conducted at 11 facilities, enrolling 59 UHL subjects and 77 normal-hearing controls (Ctrl). The first part of the study focused on standardizing the test protocol and establishing reference ranges and cut-off values. The second part analyzed the sound localization ability in UHL patients, measured by the root mean squared (RMS) error. The association between RMS values and factors such as residual hearing, contralateral routing of signal (CROS) hearing aid use, and Hearing Handicap Inventory for Adults (HHIA) scores were analyzed.

RESULTS

Reference ranges and cut-off values for the standardized sound localization test were successfully established. UHL subjects exhibited significantly higher RMS values (i.e., poorer localization) compared to controls. The use of CROS hearing aids did not improve performance, and the contribution of pinna-induced spectral cues was limited. Significant associations were found between RMS values and both sound presentation position and the number of audiogram frequencies with thresholds better than 40 dB and 50 dB, with the 50 dB threshold criterion being a more prominent factor. HHIA emotional and social scores were significantly associated only with age and not with sound localization performance or other audiological factors.

CONCLUSIONS

The standardized sound localization test proved to be a reliable tool for multicenter studies. Patients with UHL have significantly impaired sound localization. Residual hearing in the impaired ear, even if limited, was found to aid localization, whereas the benefits of CROS hearing aids and monaural spectral cues were negligible in our cohort. Since only age influenced the self-perceived hearing handicap (HHIA scores), it is crucial to consider restoring binaural hearing not just to improve sound localization but also to address the broader quality-of-life issues associated with UHL.