[The study on horizontal sound localization ability in patients with unilateral sensorineural hearing loss]

Objective: To investigate the factors influencing horizontal sound localization ability in patients with unilateral sensorineural hearing loss (USHL), with the aim of providing evidence-based guidance for clinical rehabilitation. Methods: This cross-sectional study included 43 patients diagnosed with USHL (22 males, 21 females; age range: 30-60 years, mean age: 46.5 years), recruited from Beijing Chaoyang Hospital, Capital Medical University, between October 2023 and April 2024. A control group of 20 age-matched normal-hearing participants (8 males, 12 females; mean age: 45.5 years) was also enrolled. Data collected included demographic variables, four-frequency pure-tone averages (4fPTA at 500, 1 000, 2 000, and 4 000 Hz) for both ears, and duration of hearing loss. Based on the residual hearing in the affected ear, USHL patients were divided into a group with residual hearing (defined as having at least one frequency threshold ≤65 dBHL) and a group with no detectable hearing (all frequencies >65 dBHL). Furthermore, patients in the residual hearing group were categorized by hearing loss severity into those with moderate hearing loss (35 dBHL ≤4fPTA <50 dBHL) and those with moderate-to-severe hearing loss (4fPTA≥50 dBHL). All participants underwent horizontal sound localization testing using speech stimuli under four listening conditions: quiet, and noise at signal-to-noise ratios (SNRs) of +5 dB, 0 dB, and -5 dB. Localization performance was quantified using root-mean-square error (RMSE), and data were analyzed using two-way ANOVA and Pearson correlation in SPSS 26.0. Results: Both the degree of hearing loss and background SNR significantly influenced localization accuracy (hearing level: F=47.59, P<0.01; SNR: F=69.79, P<0.01), with a significant interaction between the two factors (F=2.81, P<0.01). In quiet environments, even patients with moderate hearing loss demonstrated significantly poorer localization performance compared to normal-hearing controls (P<0.01). Among those with residual hearing, localization ability at SNR=+5 dB was not significantly different from that in quiet (P>0.05), but performance deteriorated significantly at SNR=0 dB (P<0.001). In contrast, patients without residual hearing exhibited significant deficits even at SNR=+5 dB (P<0.001). Pearson correlation analysis revealed no significant association between RMSE and sex, age, or duration of hearing loss (all P>0.05). However, a strong positive correlation was observed between hearing loss severity and RMSE across all noise conditions (r=0.760-0.800, all P<0.001), indicating that worse hearing thresholds were associated with poorer localization performance. Conclusions: Even moderate unilateral sensorineural hearing loss can impair horizontal sound localization, and this deficit is exacerbated by increasing hearing loss severity and background noise. Both hearing threshold and SNR are key determinants of localization ability and should be prioritized when designing individualized rehabilitation and intervention strategies for USHL patients.