Spatial Release from Masking with Simulated Electric–Acoustic and Cochlear Implant Speech

Background/Objectives: Spatial release from masking (SRM) refers to the improvement in speech understanding that occurs when a target talker is spatially separated from competing speech. Although normal-hearing (NH) listeners benefit substantially from spatially separating the maskers from the target, cochlear implant (CI) users experience markedly reduced advantages due to degraded spectral and binaural cue transmission. Electric–acoustic stimulation (EAS), which preserves low-frequency acoustic hearing in combination with electric stimulation, may partially restore these cues, but its benefits at small, conversationally relevant spatial separations remain poorly understood. Methods: This study measured speech identification thresholds using Coordinate Response Measure (CRM) sentences in NH listeners using natural, EAS, and simulated CI speech across five spatial configurations (0°, ±5°, ±10°, ±15°, ±30°). Speech identification thresholds were measured using a one-up/one-down adaptive procedure with Coordinate Response Measure (CRM) sentences. CI simulation used an eight-channel noise-band vocoder, whereas EAS simulation replaced the two lowest-frequency vocoder channels with low-pass speech (≤500 Hz). All stimuli were spatialized using head-related impulse responses generated from a validated virtual-acoustics model. Results: All stimulus types showed improved thresholds with increasing spatial separation; however, the magnitude of spatial release from masking (SRM) varied systematically. Natural speech produced the lowest thresholds and largest SRM, EAS speech yielded intermediate benefits, and simulated CI speech produced the smallest improvements. Notably, EAS and CI simulations were comparable at small separations, but EAS provided significantly greater SRM at ±15° and ±30°. Conclusions: These findings demonstrate that even partial low-frequency acoustic preservation enhances SRM at moderate spatial separations, highlighting the importance of EAS configurations for improving spatial hearing in CI-related listening environments.