The role of head movement in sound localization compensation in individuals with single-sided deafness

The most important cues for sound-source localization in normal hearing (NH) individuals are interaural time differences (ITDs) and interaural level differences (ILDs), information that is lacking in patients with single-sided deafness (SSD). Findings from previous studies suggested that longer duration of deafness correlated with better ability of sound localization despite the sustained absence of these binaural cues in SSD patients. To investigate the role of head movements in the compensatory mechanisms of sound localization, we performed sound localization tests for patients with congenital SSD under both head-fixed and head-moveable conditions. A total of 35 congenital SSD patients and 33 NH individuals were included, and sound localization tests were performed in a horizontal 360° sound field using warble tones of 500 and 3000 Hz. The accuracy rate and root mean square (RMS) error of the deviation angle were calculated. Head movement significantly increased sound localization accuracy in both the SSD and NH groups, as evidenced by higher accuracy rates and lower RMS errors. Compared with the NH group, the SSD group presented significantly longer reaction times for both sound signals only under the head-movable condition. Compared with NH participants, SSD patients presented significantly greater differences in RMS errors and accuracy rates for 3000 Hz warble tones between the head-fixed and head-movable conditions. Our findings suggest that the differences in the received acoustic signals due to different head orientations provide important clues for sound localization in SSD patients and may be one of the crucial compensatory strategies.