title: Hidden Markov model and support vector machine based decoding of finger movements using electrocorticography.
abstract: OBJECTIVE
  Support vector machines (SVM) have developed into a gold standard for accurate classification in brain-computer interfaces (BCI). The choice of the most appropriate classifier for a particular application depends on several characteristics in addition to decoding accuracy. Here we investigate the implementation of hidden Markov models (HMM) for online BCIs and discuss strategies to improve their performance.
  
  
  METHODS
  We compare the SVM, serving as a reference, and HMMs for classifying discrete finger movements obtained from electrocorticograms of four subjects performing a finger tapping experiment. The classifier decisions are based on a subset of low-frequency time domain and high gamma oscillation features.
  
  
  RESULTS
  We show that decoding optimization between the two approaches is due to the way features are extracted and selected and less dependent on the classifier. An additional gain in HMM performance of up to 6% was obtained by introducing model constraints. Comparable accuracies of up to 90% were achieved with both SVM and HMM with the high gamma cortical response providing the most important decoding information for both techniques.
  
  
  CONCLUSIONS
  We discuss technical HMM characteristics and adaptations in the context of the presented data as well as for general BCI applications. Our findings suggest that HMMs and their characteristics are promising for efficient online BCIs.
authors.affiliation: Chair for Healthcare Telematics and Medical Engineering, Otto-von-Guericke-University Magdeburg, Postfach 4120, D-39016 Magdeburg, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Wissel
authors.forename: Tim
authors.initials: T
authors.lastname: Pfeiffer
authors.forename: Robert
authors.initials: R
authors.lastname: Frysch
authors.forename: Robert T
authors.initials: RT
authors.lastname: Knight
authors.forename: Edward F
authors.initials: EF
authors.lastname: Chang
authors.forename: Hermann
authors.initials: H
authors.lastname: Hinrichs
authors.forename: Jochem W
authors.initials: JW
authors.lastname: Rieger
authors.forename: Georg
authors.initials: G
authors.lastname: Rose
mesh_terms: D000293:Adolescent; D000328:Adult; D000465:Algorithms; D001185:Artificial Intelligence; D062207:Brain-Computer Interfaces; D003627:Data Interpretation, Statistical; D004566:Electrodes; D004569:Electroencephalography / Q000295:instrumentation* / Q000379:methods; D005385:Fingers / Q000502:physiology*; D006801:Humans; D008297:Male; D008390:Markov Chains; D008959:Models, Neurological; D009068:Movement / Q000502:physiology*; D060388:Support Vector Machine; D055815:Young Adult
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