Empower Real-World BCIs with NIRS-X: An Adaptive Learning Framework that Harnesses Unlabeled Brain Signals

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Brain-Computer Interfaces (BCIs) using functional near-infrared spectroscopy (fNIRS) hold promise for future interactive user interfaces due to their ease of deployment and declining cost. However, they typically require a separate calibration process for each user and task, which can be burdensome. Machine learning helps, but faces a data scarcity problem. Due to inherent inter-user variations in physiological data, it has been typical to create a new annotated training dataset for every new task and user. To reduce dependence on such extensive data collection and labeling, we present an adaptive learning framework, NIRS-X, to harness more easily accessible unlabeled fNIRS data. NIRS-X includes two key components: NIRSiam and NIRSformer. We use the NIRSiam algorithm to extract generalized brain activity representations from unlabeled fNIRS data obtained from previous users and tasks, and then transfer that knowledge to new users and tasks. In conjunction, we design a neural network, NIRSformer, tailored for capturing both local and global, spatial and temporal relationships in multi-channel fNIRS brain input signals. By using unlabeled data from both a previously released fNIRS2MW visual $n$-back dataset and a newly collected fNIRS2MW audio $n$-back dataset, NIRS-X demonstrates its strong adaptation capability to new users and tasks. Results show comparable or superior performance to supervised methods, making NIRS-X promising for real-world fNIRS-based BCIs.