Auditory Perception as a Surrogate for Auditory Imagery in EEG-Based BCI Training: Neural Evidence and a Feasibility...

Brain-computer interface (BCI) systems are commonly classified as reactive or active. Reactive BCIs rely on responses to external stimuli, simplifying decoding but limiting direct user control. In contrast, active BCIs enable intuitive control through spontaneous mental activity but impose greater signal-processing challenges. Speech BCIs, a subset of active systems, hold promise for individuals with severe neurological impairments such as locked-in syndrome (LIS), potentially enabling communication through imagined speech. However, their adoption is hindered by the demanding pre-training required to collect imagery data, which often induces fatigue, and the difficulty many users face in generating consistent, high-quality imagery. To address these limitations, we propose a hybrid BCI framework that uses passive listening tasks as a surrogate for auditory imagery tasks during model training. As a first step, this proof-of-concept feasibility study examined neural responses to five Japanese vowels (/a/, /i/, /u/, /e/, /o/) under listening and imagery conditions in a limited experimental setting with healthy male participants, using event-related potentials (ERPs), topographical mapping, and event-related spectral perturbations (ERSPs), followed by statistical analysis of shared and distinct neural patterns. In the primary three-class and binary classification analyses, classification accuracies for imagery signals obtained from models trained solely on listening data were comparable to, and in some settings higher than, those trained directly on imagery data, with both outperforming chance level. These findings indicate that passive listening may provide effective training data for active auditory imagery BCIs within the tested setting, potentially reducing cognitive demands without compromising performance. Further validation in larger and more diverse cohorts is required before clinical application.