User Tutorial:Performing a P300 Spelling Session
This step assumes that you created a subject-specific configuration file for the on-line speller, as described in the previous step of this tutorial.
When performing a P300 Spelling Session, start BCI2000 by running batch/P3Speller_<Your_Amplifier>.bat, then load one of the user-specific parameter files created previously. To perform a copy spelling session -- one in which the subject has to spell a predefined text displayed on the screen --, load <SubjectName>_CopySpelling.prm. To perform a free spelling session, load <SubjectName>_FreeSpelling.prm.
Click Set Config to view the EEG signal, and prepare the subject for EEG recording according to the instructions below.
Note: When your latency value does not refer to an exact sample position, a warning message will be displayed once you click SetConfig. You may safely ignore that warning message for now.
Instructions to the Subject
On the subject's screen, a speller matrix the subject is already familiar with from the initial session is presented. Differently from that session, there is no text suggested; rather, the subject may choose freely which letters, words, and sentences to write.
- You will see a speller matrix, containing letters, numbers, and punctuation marks.
- To choose a certain letter, concentrate on it by counting the number of flashes that occur for it.
- After some time, a result will be classified and appended to the text field located at the top of the window.
- If the letter that appeared is not what you intended, concentrate on the "backspace" or "undo" field to remove it.
Additional instructions should be given regarding minimization of artifacts from
- Contraction of the muscles of the face/head, swallowing;
- Eye blinks and eye movements;
Provided that subjects are asked to minimize artifacts (e.g. asked to try to swallow only during the pause between letters), he/she should be further assisted in these efforts by providing a comfortable chair and a dimly lit room. The experimenter must carefully monitor the EEG and alert the subject in the case he/she has forgotten some of the instructions. When the experimenter is sure that his/her instructions have been well understood, the recording session may start.
- Click the "Start" button to start the spelling experiment.
Once a run has ended, BCI2000 goes into suspended state. Further runs will be added to the session when you click Resume.
When starting the next session, don't forget to increment the SessionNumber parameter on the Storage tab. Otherwise, new runs will be added to the previous session's directory. Still, as a safety net, BCI2000 will never overwrite existing data files but increment the largest run number that exists in a session directory. Moreover, it documents date and time in the StorageTime parameter. This allows to later associate data files with multiple sessions by their time and date, even if the SessionNumber parameter has not been increased.
Here, the P300 speller tutorial is finished.
Congratulations! You are now able to perform P300 spelling experiments.