User Tutorial:Configuring Online Feedback
This tutorial step assumes that you have performed and analyzed an initial session. Now you are going to create a subject-specific parameter configuration for on-line feedback.
Starting up BCI2000
Start BCI2000 using the appropriate batch file at batch/CursorTask_<YourAmplifier>.bat. You might consider creating a link to this file on the desktop.
This CursorTask will be used to configure the BCI2000 program for this specific subject. Multiple configuration sessions are typically needed to determine the proper classifier matrix for any one subject.
Now, we will construct a full parameter file that is specific to that subject:
- Begin by loading the parameter file saved previously
- In the Storage tab:
- Change the SourceData field to \task as opposed to \screening
- Change the SubjectName field to the subject's initials
- Make sure the SubjectSession field is set to 001 and SubjectRun is set to 01
The Spatial Filter
The Spatial Filter artificially weighs the incoming data from the electrodes based on their placement on the scalp of the subject. Because we are targeting specific areas of the brain to monitor, the spatial filter allows the program to identify when the electrode of interest is activating specifically. This is done by subtracting the average of the surrounding electrodes' data from the electrode of interest. For example, as seen to the right the output channel C3_OUT is the data from C3 minus one-quarter of F3, T7, Cz, and Pz.
The Classifier Matrix
The Classifier Matrix applies weights to the incoming data that allows the program to accurately identify Mu Rhythm signals. This is opened by selecting Edit Matrix next to the Classifier parameter in the Filtering tab.
- Set Number of columns to 4, and Number of rows to 1. Click Set new matrix size to apply your changes.
- In the first column (of the first row), labeled input channel, enter C3_OUT if the right hand are being used, C4_OUT for the left hand, or Cz_OUT for the feet.
- If both hands are being used, set Number of rows to 2, and click Set new matrix size. Enter C3_OUT under input channel in the first row, and C4_OUT in the second.
- In the second column, labeled input element (bin), enter feedback frequency in Hz, immediately followed with Hz, as in 12Hz.
- In the third column, enter the value 2. This corresponds to the control channel for vertical control of the cursor.
- In the fourth column, enter 1 as the weight. For further calibration, this weight can be increased to give stronger control or decreased to give finer control.
- Finally, save your configuration in a parameter file wherever you find appropriate.
In the next step, you will learn how to actually perform a Mu rhythm feedback session using the configuration created in the present step.