PEBL Continuous Performance Task-AX  (CPT-AX), a continuous
performance task modeled after a set of classic paradigms.
See  Lee, J. & Park, S. (2006). The role of stimulus saliance in CPT-AX performane 
  of schizophrenia patients.  Schizophrenia research, 81, 191-197.
  http://www.vanderbilt.edu/parklab/Lee_Park_CPT_2006.pdf

