Dynamic Interaction Between Structural Asymmetry and Attention in the Right-Ear Advantage Revealed by MEG-Based ASSRs

Background/Objectives: The dichotic listening test (DLT) is widely used to assess auditory attention and hemispheric language lateralization, with the right-ear advantage (REA) representing a robust behavioral phenomenon. Although the REA is often attributed to structural asymmetries in auditory pathways and left-hemisphere dominance for speech processing, the neural mechanisms by which selective attention modulates this asymmetry remain unclear. This study examined how directed auditory attention influences the REA and its neural correlates using magnetoencephalography (MEG)-based auditory steady-state responses (ASSRs). Methods: Fifteen right-handed participants performed directed-attention dichotic listening tasks during MEG recording. One participant was excluded from MEG analyses due to excessive noise contamination, resulting in 14 participants included in neural analyses. Participants attended to either the left or right ear throughout each session and reported the perceived stimulus from the attended ear. Dichotic speech stimuli were amplitude-modulated at 35 Hz and 45 Hz for frequency tagging. ASSR amplitudes were extracted from the left and right auditory cortices and analyzed in relation to behavioral accuracy using correlation analyses and analysis of covariance (ANCOVA). Results: Behavioral accuracy was significantly higher during right-ear attention than left-ear attention, indicating a residual REA. ASSR amplitudes tended to be higher during left-ear attention. Importantly, during left-ear attention, ASSR amplitude in the left auditory cortex showed a significant positive correlation with behavioral accuracy, whereas no such association was observed during right-ear attention. Conclusions: These findings indicate that the REA reflects a dynamic interaction between structural auditory asymmetry and top-down attentional control, with successful left-ear listening relying on compensatory recruitment of the left auditory cortex.