The purpose of this study was to evaluate the effect of natural, undirected head orientation on speech perception in the presence of interfering speech maskers that were symmetrically arranged to minimize the better-ear advantage. We also examined the characteristics of natural head motion under these conditions. Fourteen normal-hearing adults participated in continuous number categorization tasks under both head-fixed and head-free conditions. Three parameters were measured across different spatial listening configurations: (1) speech reception threshold (SRT) in both co-located and spatially separated masker conditions (±30° azimuth), (2) accuracy with spatially separated maskers at a fixed target-to-masker ratio (TMR), and (3) functional spatial boundary (FSB) in an adaptive masker-location condition. No significant differences in speech perception performance were observed between head-fixed and head-free conditions across all listening configurations. However, performance changes relative to the head-fixed condition were significantly correlated with head-orientation magnitude in the co-located SRT and FSB conditions. Exploratory analyses further indicated that larger head rotations were sometimes associated with performance improvements, whereas smaller rotations occasionally accompanied performance decrements. These observations may reflect complex interactions between dynamic spatial cues produced by head motion and moment-to-moment variations in task engagement. However, these observations warrant cautious interpretation and may provide a basis for future investigations into the role of natural head movement in spatial listening.
Radically different