Influence of Attentional State on EEG-Based Motor Imagery of Lower Limb

Penghai Li^1*Dongfang Yu¹Longlong Cheng^2*Kun Wang²

• ¹Tianjin University of Technology, Tianjin, China
• ²Tianjin University, Tianjin, Tianjin, China

Introduction: Motor imagery (MI) has emerged as a promising technique for enhancing motor skill acquisition and facilitating neural adaptation training. Attention plays a key role in regulating the neural mechanisms underlying MI. This study aims to investigate how attentional states modulate EEG-based lower limb motor imagery performance by influencing event-related desynchronization (ERD) and the Alpha Modulation Index (AMI), and to develop a real-time attention monitoring method based on the theta/beta ratio (TBR).Methods: Fourteen healthy right-handed subjects (aged 21-23) performed right-leg MI tasks while their attentional states were modulated via a key-press paradigm. EEG signals were recorded using a 32-channel system and preprocessed with independent component analysis (ICA) to remove artifacts. Attentional states were quantified using both the traditional offline AMI and the real-time TBR index, with time-frequency analysis applied to assess ERD and its relationship with attention.Results: Results indicated a significant increase in ERD during high attentional states compared to low attentional states, with AMI values showing a strong positive correlation with ERD (r = 0.9641, p < 0.01). Cluster-based permutation testing confirmed that this α-band ERD difference was significant (corrected p < 0.05). Moreover, the TBR index proved to be an effective real-time metric, decreasing significantly under focused attention. Offline paired t-tests showed a significant TBR reduction (t(13)=5.12, p=2.4×10⁻⁵), and online analyses further validated second-by-second discrimination (Bonferroni-corrected p < 0.01). These findings confirm the feasibility and efficacy of TBR for real-time attention monitoring and suggest that enhanced attentional focus during lower limb MI can improve signal quality and overall performance.Conclusion: This study reveals that attentional states significantly influence the neural efficiency of lower limb motor imagery by modulating ERD/AMI, and demonstrates that the TBR can serve as a real-time indicator of attention, providing a novel tool for optimizing attentional processes in motor skill training.