title: Use of high-frequency visual stimuli above the critical flicker frequency in a SSVEP-based BMI.
abstract: OBJECTIVE
  This study presents a new steady-state visual evoked potential (SSVEP)-based brain-machine interface (BMI) using flickering visual stimuli at frequencies greater than the critical flicker frequency (CFF).
  
  
  METHODS
  We first asked participants to fixate on a green/blue flicker (30-70Hz), and SSVEP amplitude was evaluated. Participants were asked to indicate whether the stimulus was visibly flickering and to report their subjective level of discomfort. We then assessed visibly (41, 43, and 45Hz) vs. invisibly (61, 63, and 65Hz) flickering stimulus in an SSVEP-based BMI. Visual fatigue was assessed via the flicker test before and after operation of the BMI.
  
  
  RESULTS
  Higher frequency stimuli reduced participants' subjective discomfort. Participants successfully controlled the SSVEP-based BMI using both the visibly and invisibly flickering stimuli (93.1% and 88.0%, respectively); the flicker test revealed a decrease in CFF (i.e., visual fatigue) under the visible condition only (-5.7%, P<0.001).
  
  
  CONCLUSIONS
  The use of high-frequency visual stimuli above the CFF led to high classification accuracy and decreased visual fatigue in an SSVEP-based BMI.
  
  
  CONCLUSIONS
  High-frequency flicker stimuli above the CFF were able to induce SSVEPs and may prove useful in the development of BMI-based assistive products.
authors.affiliation: Systems Neuroscience Section, Department of Rehabilitation for Brain Functions, Research Institute of National Rehabilitation Center for Persons with Disabilities, Tokorozawa, Saitama 359-8555, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Sakurada
authors.affiliation: Systems Neuroscience Section, Department of Rehabilitation for Brain Functions, Research Institute of National Rehabilitation Center for Persons with Disabilities, Tokorozawa, Saitama 359-8555, Japan.
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Kawase
authors.affiliation: Systems Neuroscience Section, Department of Rehabilitation for Brain Functions, Research Institute of National Rehabilitation Center for Persons with Disabilities, Tokorozawa, Saitama 359-8555, Japan.
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Komatsu
authors.affiliation: Systems Neuroscience Section, Department of Rehabilitation for Brain Functions, Research Institute of National Rehabilitation Center for Persons with Disabilities, Tokorozawa, Saitama 359-8555, Japan; Brain Science Inspired Life Support Research Center, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan. Electronic address: kansaku-kenji@rehab.go.jp.
authors.forename: Kenji
authors.initials: K
authors.lastname: Kansaku
mesh_terms: D000328:Adult; D062207:Brain-Computer Interfaces; D004569:Electroencephalography / Q000379:methods*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D005425:Flicker Fusion / Q000502:physiology*; D006801:Humans; D008297:Male; D010775:Photic Stimulation / Q000379:methods*; D055815:Young Adult
keywords: BCI; BMI; Critical flicker frequency; SSVEP; Visual fatigue