title: Automatic single-trial discrimination of mental arithmetic, mental singing and the no-control state from prefrontal activity: toward a three-state NIRS-BCI.
abstract: BACKGROUND
  Near-infrared spectroscopy (NIRS) is an optical imaging technology that has recently been investigated for use in a safe, non-invasive brain-computer interface (BCI) for individuals with severe motor impairments. To date, most NIRS-BCI studies have attempted to discriminate two mental states (e.g., a mental task and rest), which could potentially lead to a two-choice BCI system. In this study, we attempted to automatically differentiate three mental states - specifically, intentional activity due to 1) a mental arithmetic (MA) task and 2) a mental singing (MS) task, and 3) an unconstrained, "no-control (NC)" state - to investigate the feasibility of a three-choice system-paced NIRS-BCI.
  
  
  RESULTS
  Deploying a dual-wavelength frequency domain near-infrared spectrometer, we interrogated nine sites around the frontopolar locations while 7 able-bodied adults performed mental arithmetic and mental singing to answer multiple-choice questions within a system-paced paradigm. With a linear classifier trained on a ten-dimensional feature set, an overall classification accuracy of 56.2% was achieved for the MA vs. MS vs. NC classification problem and all individual participant accuracies significantly exceeded chance (i.e., 33%). However, as anticipated based on results of previous work, the three-class discrimination was unsuccessful for three participants due to the ineffectiveness of the mental singing task. Excluding these three participants increases the accuracy rate to 62.5%. Even without training, three of the remaining four participants achieved accuracies approaching 70%, the value often cited as being necessary for effective BCI communication.
  
  
  CONCLUSIONS
  These results are encouraging and demonstrate the potential of a three-state system-paced NIRS-BCI with two intentional control states corresponding to mental arithmetic and mental singing.
authors.affiliation: Bloorview Research Institute, Holland Bloorview Kids Rehabilitation Hospital, Toronto, Canada.
authors.forename: Sarah D
authors.initials: SD
authors.lastname: Power
authors.forename: Azadeh
authors.initials: A
authors.lastname: Kushki
authors.forename: Tom
authors.initials: T
authors.lastname: Chau
mesh_terms: D000328:Adult; D062207:Brain-Computer Interfaces; D004192:Discrimination, Psychological / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008433:Mathematics; D009146:Music; D017397:Prefrontal Cortex / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D063346:Singing; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D011795:Surveys and Questionnaires; D055815:Young Adult