title: A visual parallel-BCI speller based on the time-frequency coding strategy.
abstract: OBJECTIVE
  Spelling is one of the most important issues in brain-computer interface (BCI) research. This paper is to develop a visual parallel-BCI speller system based on the time-frequency coding strategy in which the sub-speller switching among four simultaneously presented sub-spellers and the character selection are identified in a parallel mode.
  
  
  METHODS
  The parallel-BCI speller was constituted by four independent P300+SSVEP-B (P300 plus SSVEP blocking) spellers with different flicker frequencies, thereby all characters had a specific time-frequency code. To verify its effectiveness, 11 subjects were involved in the offline and online spellings. A classification strategy was designed to recognize the target character through jointly using the canonical correlation analysis and stepwise linear discriminant analysis.
  
  
  RESULTS
  Online spellings showed that the proposed parallel-BCI speller had a high performance, reaching the highest information transfer rate of 67.4 bit min(-1), with an average of 54.0 bit min(-1) and 43.0 bit min(-1) in the three rounds and five rounds, respectively.
  
  
  CONCLUSIONS
  The results indicated that the proposed parallel-BCI could be effectively controlled by users with attention shifting fluently among the sub-spellers, and highly improved the BCI spelling performance.
authors.affiliation: Department of Biomedical Engineering, Tianjin University, Tianjin, People's Republic of China. Tianjin Key Laboratory of Biomedical Detecting Techniques and Instruments, Tianjin, People's Republic of China.
authors.forename: Minpeng
authors.initials: M
authors.lastname: Xu
authors.forename: Long
authors.initials: L
authors.lastname: Chen
authors.forename: Lixin
authors.initials: L
authors.lastname: Zhang
authors.forename: Hongzhi
authors.initials: H
authors.lastname: Qi
authors.forename: Lan
authors.initials: L
authors.lastname: Ma
authors.forename: Jiabei
authors.initials: J
authors.lastname: Tang
authors.forename: Baikun
authors.initials: B
authors.lastname: Wan
authors.forename: Dong
authors.initials: D
authors.lastname: Ming
mesh_terms: D000328:Adult; D062207:Brain-Computer Interfaces; D004569:Electroencephalography / Q000379:methods*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods*; D013997:Time Factors; D055815:Young Adult