Spatial hearing adaptation in congenital and acquired single-sided deafness

Spatial hearing depends on binaural integration of interaural time and level differences and monaural spectral cues. Single-sided deafness (SSD) disrupts this process, impairing localization and speech perception. Congenital (SSDc) and acquired (SSDa) SSD provide unique models for studying cortical adaptation, while cochlear implantation (CI) offers partial restoration of binaural hearing. This study examined differences in localization performance and response promptness across SSDc, SSDa, and SSD-CI listeners.

Thirty-one SSD listeners (9 SSDc, 11 SSDa, and 11 SSD-CI) and 16 normal-hearing (NH) controls completed broadband noise localization tasks in azimuth (90°) and elevation (30°). Azimuth and elevation localization, bias, mean absolute error (MAE), and response promptness were analyzed using linear regression and mixed-effects models.

SSD-CI listeners with CI on demonstrated significantly improved azimuth localization compared to CI off (gain = 0.97 vs. 0.26, MAE = 27°, vs. 47°, p < 0.001). SSDc listeners performed more accurately than SSDa (gain = 0.57 vs. 0.17, p < 0.001), consistent with enhanced adaptation to monaural cues following early deprivation. All SSD groups showed poor vertical localization on the deaf side (gain = 0.15) and slower responses (mean = 2.17 s^-1), compared to NH (4.02 s^-1, p < 0.037). CI was associated with faster responses, suggesting improved processing efficiency.

Early deprivation in SSDc promotes compensatory strategies for spatial hearing, while SSDa shows more limited adaptation. CI can partially reintroduce binaural cues, improving horizontal localization and processing efficiency, though vertical localization deficits persist.

These findings demonstrate that auditory experience and hearing restoration jointly influence spatial hearing behavior. Understanding these adaptive patterns can guide individualized rehabilitation strategies and optimize outcomes for individuals with unilateral hearing loss.