Nozomu Nishikawa Yoshihiro Matsumoto Shoji Makino Tomasz M. Rutkowski The Spatial Real and Virtual Sound Stimuli Optimization for the Auditory BCI http://arxiv.org/abs/1210.2945 2012 CoRR abs/1210.2945 db/journals/corr/corr1210.html#abs-1210-2945