title: Context-aware adaptive spelling in motor imagery BCI.
abstract: This work presents a first motor imagery-based, adaptive brain-computer interface (BCI) speller, which is able to exploit application-derived context for improved, simultaneous classifier adaptation and spelling. Online spelling experiments with ten able-bodied users evaluate the ability of our scheme, first, to alleviate non-stationarity of brain signals for restoring the subject's performances, second, to guide naive users into BCI control avoiding initial offline BCI calibration and, third, to outperform regular unsupervised adaptation.
  
  
  
  Our co-adaptive framework combines the BrainTree speller with smooth-batch linear discriminant analysis adaptation. The latter enjoys contextual assistance through BrainTree's language model to improve online expectation-maximization maximum-likelihood estimation.
  
  
  
  Our results verify the possibility to restore single-sample classification and BCI command accuracy, as well as spelling speed for expert users. Most importantly, context-aware adaptation performs significantly better than its unsupervised equivalent and similar to the supervised one. Although no significant differences are found with respect to the state-of-the-art PMean approach, the proposed algorithm is shown to be advantageous for 30% of the users.
  
  
  
  We demonstrate the possibility to circumvent supervised BCI recalibration, saving time without compromising the adaptation quality. On the other hand, we show that this type of classifier adaptation is not as efficient for BCI training purposes.
authors.affiliation: Chair in Brain-Machine Interface, Center for Neuroprosthetics, Institute of Bioengineering, School of Engineering, École Polytechnique Fédérale de Lausanne, Campus Biotech H4, Chemin des Mines 9, CH-1202, Geneva, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Perdikis
authors.forename: R
authors.initials: R
authors.lastname: Leeb
authors.forename: J D R
authors.initials: JD
authors.lastname: Millán
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D000465:Algorithms; D001364:Awareness; D062207:Brain-Computer Interfaces; D003143:Communication Devices for People with Disabilities; D016002:Discriminant Analysis; D004569:Electroencephalography; D005260:Female; D006801:Humans; D007802:Language; D008297:Male; D011597:Psychomotor Performance; D011930:Reaction Time; D015203:Reproducibility of Results