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A Hybrid Factor Graph Model for Biomedical Activity Detection

Mareike Stender; Jan Graßhoff; Tanya Braun; Ralf Möller; Philipp Rostalski
In: 2021 IEEE EMBS International Conference on Biomedical and Health Informatics (BHI) (IEEE BHI 2021). IEEE-EMBS International Conference on Biomedical and Health Informatics (BHI-2021), July 27-30, Athens, Greece, ISBN 978-1-6654-0358-0, IEEE Xplore, 7/2021.


For activity detection on biomedical time-series data, biomedical signals are modeled as a switching linear dynamical system with random variables, including discrete and continuous dynamics. We present a formalism for representing a system's joint probability density function as a hybrid factor graph. Solving inference problems is based on belief propagation using message passing. Inference results yield the activity estimations in terms of probability distributions instead of binary decisions. This work builds on previous efforts to consolidate factor graphs as unifying representations for signal processing algorithms. We show that the formalism can be successfully applied to detect activities in surface electromyography data acquired during walking. The modularity of factor graphs enables the straightforward adoption and extension of the formalism expanding its scope of application.