title: Long-term evaluation of a 4-class imagery-based brain-computer interface.
abstract: OBJECTIVE
  The study aimed to improve brain-computer interface (BCI)-usability by using distinct control strategies and evaluating performance, brain activity and psychological variables on a long-term basis over several months.
  
  
  METHODS
  Fourteen able-bodied users participated in 10 sessions, plus a follow-up session. Users were trained to control an EEG-based 4-class BCI with the mental tasks, word association, mental subtraction, spatial navigation, and motor imagery.
  
  
  RESULTS
  Eight users reached mean accuracies of 61-72% and managed to control all 4 classes above chance in single-sessions. Performance and brain patterns stayed stable over 10 weeks without training. Motor imagery showed the best performance and most distinct brain patterns. Participants' fear of incompetence decreased while the quality of their imagery and task ease increased over sessions. The evaluation of feedback differed between tasks and correlated with performance.
  
  
  CONCLUSIONS
  Users can control a real-time 4-class BCI, driven by distinct mental tasks, with stable performance over months. However, general performance was rather low for effective BCI control in daily life. Possibilities for future optimizations to increase performance are discussed.
  
  
  CONCLUSIONS
  The evaluation of alternatives to motor imagery, long-term BCI use, and psychological variables is important to improve usability for mental imagery-based BCIs.
authors.affiliation: Department of Psychology, University of Graz, Universitätsplatz 2/III, 8010 Graz, Austria.
authors.forename: Elisabeth V C
authors.initials: EV
authors.lastname: Friedrich
authors.forename: Reinhold
authors.initials: R
authors.lastname: Scherer
authors.forename: Christa
authors.initials: C
authors.lastname: Neuper
mesh_terms: D000328:Adult; D001676:Biofeedback, Psychology; D001921:Brain / Q000502:physiology*; D062207:Brain-Computer Interfaces; D004569:Electroencephalography / Q000379:methods; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D019018:Imagery, Psychotherapy / Q000379:methods*; D008297:Male; D013997:Time Factors; D014584:User-Computer Interface; D055815:Young Adult