An Adaptive Spatial Filter for User-Independent Single Trial Detection of Event-Related Potentials
Hendrik Wöhrle, Mario Michael Krell, Sirko Straube, Su-Kyoung Kim, Elsa Andrea Kirchner, Frank Kirchner
In IEEE Transactions on Biomedical Engineering, IEEE, volume 62, number 7, pages 1696-1705, Jul/2015.
Goal: Current brain computer interfaces (BCIs) are usually based on various, often supervised, signal processing methods. The disadvantage of supervised methods is the requirement to calibrate them with recently acquired subjectspecific training data. Here, we present a novel algorithm for dimensionality reduction (spatial filter), that is ideally suited for single-trial detection of event-related potentials and can be adapted online to a new subject to minimize or avoid calibration time. Methods: The algorithm is based on the well-known xDAWN filter, but uses generalized eigendecomposition to allow an incremental training by recursive least squares updates of the filter coefficients. We analyze the effectiveness of the spatial filter in different transfer scenarios and combinations with adaptive classifiers. Results: The results show that it can compensate changes due to switching between different users, and therefore allows to reuse training data that has been previously recorded from other subjects. Conclusions: The presented approach allows to reduce or completely avoid a calibration phase and to instantly use the BCI system with only a minor decrease of performance. Significance: The novel filter can adapt a precomputed spatial filter to a new subject and make a BCI system user independent.
Brain Computer Interfaces, Adaptation, Spatial