Cortical reorganization and listening effort in sound localization with left- vs. right-sided deafness.

Sound source localization is a fundamental ability for living organisms and essential for human daily functioning. Sound localization heavily relies on binaural auditory input. Unilateral auditory impairment not only disrupts sound localization but also alters cortical activation patterns. However, current understanding of these adaptive cortical changes remains limited, with a lack of multidimensional and systematic research. Here, we employed multimodal neuroimaging-functional near-infrared spectroscopy (fNIRS) and pupillometry-to investigate the physiological mechanisms of sound localization from complementary perspectives. We recruited 33 normal-hearing participants, 12 with right single-sided deafness (RSSD), and 8 with left single-sided deafness (LSSD). All participants completed a sound localization task with seven azimuths (±90°, ±60°, ±30°, 0°) in the frontal hemifield. Our results revealed symmetric activation patterns in higher-order auditory cortices within the auditory dorsal stream and distinct cognitive processing for left vs. right hemispheres during sound localization. Following unilateral auditory deprivation, we observed distinct patterns of cortical reorganization that differed by deprivation side. Specifically, RSSD was associated with maintained spatial gradient encoding but required prefrontal compensation, whereas LSSD showed sacrificed spatial resolution for hemispheric processing efficiency. These findings offer novel insights into brain adaptation to unilateral auditory deprivation and provide a foundation for future research and clinical applications.