The P300 spelling device utilizes the fact that rare events in the oddball paradigm elicit the P300 component of the event-related potential.
The BCI presents the user with a matrix of 6 by 6 cells, each containing one letter of the alphabet. The user focuses attention on the cell containing the letter to be communicated while the rows and the columns, or the single characters of the matrix are intensified.
Each intensification is an event in the oddball sequence, the row and the column containing the attended cell (or the character itself when single cells are flashed) are rare items and, therefore, only these events elicit a P300.
The user has to distinguish between the common and the rare stimuli, by performing a mental count every time the selected target cell flashes.
The less probable the eliciting event is, the larger is the P300. This positive potential occurs around 300ms after the event occurs.
The computer thus detects the transmitted character by determining which row and which column or which character elicited the P300.

State of the Art in BCI research

University of Illinois at Urbana-Champaign
Department of Psychology and Beckman Institute

Donchin E, Spencer KM, Wijesinghe R (2000) The mental prosthesis: assessing the speed of a P300-based brain-computer interface. IEEE Trans Rehabil Eng 8:174-179

University of California, San Diego
Department of Cognitive Science

Allison BZ, Pineda JA (2003) ERPs evoked by different matrix sizes: implications for a brain computer interface (BCI) system. Neural Systems and Rehabilitation Engineering, IEEE Transactions on, 11:110-113
Serby H, Yom-Tov E, Inbar GF (2005) An improved P300-based brain-computer interface. Neural Systems and Rehabilitation Engineering, IEEE Transactions on, 13:89-98

University of Bielefeld, Germany
Faculty of Technology
Neuroinformatics Group

Meinicke, P., Kaper, M., and Hoppe, F. Improving Transfer Rates in Brain Computer Interfacing: A case study. Proceedings NIPS 2002 . 2002. Canada
Kaper, M. and Ritter, H. Progress in P300-based brain-computer interfacing. Biomedical Circuits and Systems, 2004 IEEE International Workshop on, S3.5.INV-9 - 12. 1-12-2004
Kaper M, Meinicke P, Grossekathoefer U, Lingner T, Ritter H (2004) BCI competition 2003-data set IIb: support vector machines for the P300 speller paradigm. Biomedical Engineering, IEEE Transactions on, 51:1073-1076

University of Tübingen, Germany
Institute of Medical Psychology and Behavioral Neurobiology

Bostanov V (2004) BCI competition 2003-data sets Ib and IIb: feature extraction from event-related brain potentials with the continuous wavelet transform and the t-value scalogram. Biomedical Engineering, IEEE Transactions on 51:1057-1061

Tshinghua University, Beijing
Department of Biomedical Engineering

Xu N, Gao X, Hong B, Miao X, Gao S, Yang F (2004) BCI Competition 2003--Data set IIb: enhancing P300 wave detection using ICA-based subspace projections for BCI applications. IEEE Trans Biomed Eng 51:1067-1072

Agency for Science, Technology and Research
Institute for Infocomm Research, Singapore
Neural Processing Laboratory

Cuntai, Guan, Thulasidas, M., and Jiankang, Wu. High performance P300 speller for brain-computer interface. Biomedical Circuits and Systems, 2004 IEEE International Workshop on , S3.5.INV-13 - 16. 1-3-2004
Thulasidas M, Cuntai G, Jiankang W (2006) Robust classification of EEG signal for brain-computer interface. Neural Systems and Rehabilitation Engineering, IEEE Transactions on, 14:24-29

University of South Florida
Department of Psychology

Sellers EW, Kubler A, Donchin E (2006) Brain-computer interface research at the University of South Florida Cognitive Psychophysiology Laboratory: the P300 Speller. IEEE Trans Neural Syst Rehabil Eng 14:221-224

Wadsworth Center, Albany, New York
Laboratory of Nervous System Disorders

Krusienski DJ, Sellers EW, Cabestaing F, Bayoudh S, McFarland DJ, Vaughan TM, Wolpaw JR (2006) A comparison of classification techniques for the P300 Speller. J Neural Eng 3:299-305
Sellers EW, Krusienski DJ, McFarland DJ, Vaughan TM, Wolpaw JR (2006) A P300 event-related potential brain-computer interface (BCI): the effects of matrix size and inter stimulus interval on performance. Biol Psychol 73:242-252
Sellers EW, Donchin E (2006) A P300-based brain-computer interface: initial tests by ALS patients. Clin Neurophysiol 117:538-548

National Rehabilitation Center for Persons with Disabilities
Research Institute

Komatsu, T., Hata, N., Nakajima, Y., Kansaku, K. (2008) A non-training > EEG-based > BMI system for environmental control. Neurosci Res 61: S251, Suppl .1