Brain computer interface (BCI) is a system allows a user to control external devices or to communicate with other people using only his or her thoughts. The P300 speller is one such BCI in which users input letters. For inputting letters via the P300 speller, higher accuracy and shorter input times are needed, especially given densely populated display screens. We propose a new interface with a second display in the P300 speller that the user can switch to and from by selecting the “next” or “back” commands, therby reducing the density of displayed letters and improving the performance of the P300 speller. We show the comparison results in terms of accuracy and input times between the conventional interface and proposed interface.
 J. R. Wolpaw, N. Birbaumer, D. J. McFarland, G. Pfurtscheller, and T. M. Vaughan, “Brain-computer interfaces for communication and control,” Clinical Neurophysiology, vol. 113, no. 6, pp. 767–791, 2002.
 K. Tatsuhiro and Y. Kiyoyuki, “Current studies on brain-computer-interface(bci),” in The Bulletin of School of High-Technology for Human Welfare, Tokai Univ. Tokai Univercity, 2011, pp. 7–12.
 D. Kaub-Wittemer, N. Steinbuchel, M. Wasner, G. Laier-Groeneveld, and G. Borasio, “Quality of life and psychosocial issues in ventilated patients with amyotrophic lateral sclerosis and their caregivers,” Journal of pain and symptom management, vol. 26, no. 4, pp. 890–896, 2003.
 L. Farwell and E. Donchin, “Talking off the top of your head: toward a mental prosthesis utilizing event-related brain potentials,” Electroencephalography and clinical Neurophysiology, vol. 70, no. 6, pp. 510–523, 1988.
 D. J. Krusienski, E. W. Sellers, S. Bayoudh, F. Cabestaing, D. J. McFarland, T. M. Vaughan, and J. R. Wolpaw, “A comparison of classification techniques for the p300 speller,” Journal of Neural Engineering, vol. 3, no. 4, pp. 299–305, 2006.
 H. Takahashi, T. Yoshikawa, and T. Furuhashi, “A study on application of reliability based automatic repeat request to brain computer interfaces,” in Advances in Neuro-Information Processing. Springer, 2009, pp. 1013–1020.
 B. Dal Seno, M. Matteucci, and L. Mainardi, “The utility metric: a novel method to assess the overall performance of discrete brain computer interfaces,” IEEE Transactions on Neural Systems and Rehabilitation Engineering, vol. 18, no. 1, pp. 20–28, 2010.