User Tutorial:Performing a Mu Rhythm Feedback Session

This step assumes that you created a subject-specific configuration file for the on-line system, as described in the previous step of this tutorial.

Preparation

If you quit BCI2000 after the previous step, start it using the appropriate batch file at batch/CursorFeedback_<YourAmplifier>.bat, or the link to that file which you created on the desktop.

Then, load the configuration file that you saved in the previous step.

Click Set Config to view the EEG signal, and prepare the subject for EEG recording as you did for the initial session.

Instructions to the Subject

After the subject is ready for EEG acquisition, he/she is given instructions about the experimental task.

A screen with a T in the center is initially presented. As soon as the subject is ready and the EEG traces are stabilized, the investigator will start the acquisition, and the T will disappear. For each trial, four phases will occur:

1. Target presentation. A target appears on the right edge of the screen for about one second.
2. Cursor movement. The subject receives feedback about his/her Mu amplitude by the trajectory of the cursor on the screen. The time needed for the cursor to move from the left to the right edge of the screen should be approximately three seconds.
3. Result. If the cursor hits the target, the latter changes its color; otherwise, the screen will blank. In either case, this period lasts one second.
4. Intertrial Interval. Screen will turn/remain black for one second, after which the cycle starts over.

When a target is presented, the subject must concentrate on whatever he feels can modify the cursor trajectory towards the desired direction. In other words, it is not the subject's task to perform a particular mental imagery, but it is the subject's task to control the cursor.

In the early part of the training, the experimenter will suggest that up/down movement may be achieved by imagining movement of upper/lower limbs. In fact, this is likely to produce a differential modulation of Mu rhythm over the hands (C3, C4) or feet (Cz) motor areas. After a few sessions, motor imagery typically becomes less important.

The second set of instructions to the subject regards the minimization of artifacts from

• Contraction of the muscles of the face/head, swallowing;
• Eye blinks and eye movements;
• Motion.

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. We will return to the role of reinforcement, but it is already clear that 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 feedback experiment. During the experiment, the subject's performance is written into a log window on the experimenter's screen, and recorded into a log file that is saved to disk in the session directory.

Monitoring the Recording

After recording has started, one might feel the temptation to leave the subject alone during the run since most of the experimental activities are automated in BCI2000. On the contrary, the experimenter has several tasks:

• Filling in a run-sheet to report information that is not automatically

recorded by BCI2000 and that will later help when data are analyzed.

• Monitoring the EEG waves, checking that the quality of recording does

not decrease (electrode contact failure, muscular, EOG or motion artifacts, etc.)

• Reinforce the subject: warn him/her if he/she is producing artifacts, keep

him/her alert if getting drowsy, give him/her feedback about his/her performance so that interest is kept high. The run sheet is the most important mean of communication between the technician who performs the recordings and the person who analyzes the data (or possibly the historical memory of whoever does both). It is important that it is compiled carefully and that it is rich of appearingly obvious details: only time will say what is standard and what changes from session to session, and if you will need to analyze data acquired years before, you will probably have a problem if you did not note down all information.

Multiple Sessions

Once a run has ended, BCI2000 goes into suspended state. Further runs will be added to the session when you click Resume. After the session has finished, you may want to save auto-adjusted parameters for the next session. Use Save Parameters from the configuration window to do this.

Alternatively, the Load Parameters dialog allows you to choose a data file rather than a parameter file, and thus use the configuration contained in a previous session's data file for the next session. However, parameters contained in a data file reflect the state at the beginning of the recording, so changes during a session's last run cannot be recovered that way.

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. As a safety net, BCI2000 will never overwrite existing data files, and documents date and time in the StorageTime parameter. This allows to later separate data files into runs even if the SessionNumber parameter has not been increased.

After each session, it is recommended that you analyze the recorded data in the same way as you did for the initial session. This allows you to track and adapt to signal changes in the subject's parameters that may occur in the course of learning.

Finished

Here, the Mu rhythm tutorial is finished. You should now know how to perform a simple Mu rhythm feedback experiment.

See also

User Tutorial:Mu Rhythm BCI Tutorial