Neural Markers of Auditory Symbol Learning: Multiscale EEG Evidence from Morse Code Training

To investigate how symbolic system learning induces neural plasticity, we examined the neural mechanisms of auditory symbolic processing using Morse Code (MC), a structured auditory symbolic system. In this study, novice learners underwent two months of MC training while electroencephalography (EEG) was recorded before and after training. We examined training-induced neural plasticity at two complementary levels: the local level and the global level. At the local level, MC training led to a significant decrease in N200 amplitude at the Fz electrode ( p  < 0.05), indicating reduced engagement of controlled processing and a shift toward more automated processing during the dot-count discrimination task (i.e., more efficient early task processing). At the global level, phase-locking value (PLV) analyses revealed a training-associated reorganization of task-evoked functional connectivity, with the right temporal T8 node showing increased hub-like centrality and network properties becoming more favorable for information integration and transmission. These findings suggest that, as a result of training, the brain's perception of rhythmic auditory stimuli has changed, reflecting both local processing optimization and global network reorganization. The findings were consistent with training-associated changes in task-evoked neural dynamics at both event-related potentials (ERP) and network levels, captured by candidate neural markers integrating ERP and network metrics.