Today, the maximal entropy method of autoregressive spectral estimation is preferably used for on-line analysis. Trained subjects can reach an accuracy from 70 % up to 95 % and reach the target in 1-2 s [McFarland 1997a, 1997b, 1998, Wolpaw 1998].

Two dimensional control was established by controlling horizontal movement with the sum of left and right mu power and vertical movement by the difference between left and right mu. The target was presented in one corner of the screen. The accuracy was around 60 % and the subjects needed 2-4 seconds to hit the target [Wolpaw 1994]. The ultimate goal is a mouse-like cursor control that allows to operate common mouse-driven programs [Vaughan 1996].

Miner et al. [Miner 1998] demonstrated that a BCI can be used to answer simple questions. Four trained subjects (one with ALS) controlled a vertical cursor on a video screen. The targets were replaced by the words YES and NO. Then the subjects used the cursor to answer spoken questions. The answers were confirmed by response verification. 93 % to 99 % of the questions were correctly answered and 64 % to 87 % of their answers were confirmed by the response verification. The question complexity did not interfere with the accuracy. Finally, the Wadsworth BCI appears capable of operating the "Freehand" neuroprosthesis which provides hand-grasp control to people with spinal cord injuries [Kilgore 1997, Lauer 1999].

In the first experiments, a rocket appeared on the screen whose position was determined by the SCP shift at Cz. The subjects were instructed to move the rocket and had to find their individual best strategy. The disadvantage was that the subjects could not control the brain potentials fast enough. Subjects needed at least 10 seconds to perform one action, but for real applications, a more rapid control is necessary. Therefore, the absolute negativity versus positivity measurement was replaced by the measurement of the relative negativity in two consecutive intervals. This has 2 advantages: it is not required to produce relative positivity (more difficult than negativity [Birbaumer 1981]) and a faster timing paradigm could be introduced [Kotchoubey 1997].

Birbaumer's group investigated patients who were almost totally paralyzed. The patients were trained for 4-6 weeks and learned to control their slow cortical potentials at the vertex. This shows that the control of SCPs does not require feedback loops from the periphery [Kübler 1998]. After that a Thought Translation Device (TTD) was set up in order to enable subjects to select letters on a computer screen and to write words and sentences [Birbaumer 1992, Kisil 1992, Kübler 1999]. At this time the TTD is permanently used from 3 ALS patients in Germany who were trained over a period of some months in more than 100 sessions to control the system. The patients have to produce either cortical negative or positive differences within 2 seconds in reference to a 2 second baseline interval. The difference between active and baseline interval is transformed into cursor movement on a computer monitor and allows to operate the TTD. Two of the three ALS patients achieved a classification accuracy between 70 % and 80 %. The communication rate is approximately 1 letter every 2 minutes [Birbaumer 1999a].