Mining within-trial oscillatory brain dynamics to address the variability of optimized spatial filters
This addresses the problem of selecting stable features for neurotechnological applications like brain-computer interfaces in stroke rehabilitation, though it is incremental as it builds on existing spatial filtering methods.
The paper tackled the high variability of optimized spatial filters in oscillatory brain signal analysis by clustering components based on within-trial envelope dynamics, finding an average of seven subject-specific clusters per subject that were strictly confined to frequency bands.
Data-driven spatial filtering algorithms optimize scores such as the contrast between two conditions to extract oscillatory brain signal components. Most machine learning approaches for filter estimation, however, disregard within-trial temporal dynamics and are extremely sensitive to changes in training data and involved hyperparameters. This leads to highly variable solutions and impedes the selection of a suitable candidate for, e.g.,~neurotechnological applications. Fostering component introspection, we propose to embrace this variability by condensing the functional signatures of a large set of oscillatory components into homogeneous clusters, each representing specific within-trial envelope dynamics. The proposed method is exemplified by and evaluated on a complex hand force task with a rich within-trial structure. Based on electroencephalography data of 18 healthy subjects, we found that the components' distinct temporal envelope dynamics are highly subject-specific. On average, we obtained seven clusters per subject, which were strictly confined regarding their underlying frequency bands. As the analysis method is not limited to a specific spatial filtering algorithm, it could be utilized for a wide range of neurotechnological applications, e.g., to select and monitor functionally relevant features for brain-computer interface protocols in stroke rehabilitation.