User Tutorial:Obtaining Mu Rhythm Parameters in an Initial Session
Although the basic properties of the Mu rhythm are identical for all humans, spatial patterns and exact frequencies are different across people. Thus, it is necessary to obtain these individual parameters prior to any feedback experiments, i.e., to calibrate the BCI system using data acquired from an initial session.
Experimental Design
In this initial session, the subject is instructed to imagine hand and/or foot movements in response to visual cues. To identify a subject's Mu Rhythm, offline analyses then determine the frequency and location whose activity changes the most across conditions (e.g., hand imagery and rest). These analyses result in spectra calculated at different locations or in topographical plots at particular frequencies.
Performing the Initial Session
- Start BCI2000 by double-clicking batch/StimulusPresentation_<YourAmplifier>.bat. If you are unable to find a batch file for your amplifier, please see the section on contributed BCI2000 modules. For repeated use, placing a link to this file on the desktop might be a good idea.
- In the operator module, click "Config".
- Click "Load Parameters" to load the parameter file at parms/mu_tutorial/InitialMuSession.prm.
- Load additional parameters for your amplifier by clicking "Load Parameters" again and choosing the parameter file from parms/fragments/amplifiers that corresponds to your amplifier. If you're unable to find a parameter file that corresponds to your amplifier and your amplifier is listed in the contributions section, load the SignalGenerator.prm parameter file (also located in parms/fragments/amplifiers) and modify parameters as necessary. Please see User Reference:Parameters for a listing of currently supported parameters along with their descriptions.
- When you have a separate monitor for experimenter and subject, load the parameter file at parms/fragments/stdlib/DualMonitor.prm.
- In your system's display properties configuration, make sure that the subject's monitor is configured to be located to the right of the main monitor.
- Make sure the WindowLeft parameter matches the main monitor's actual pixel width.
- You may need to adapt WindowTop, WindowWidth, and WindowHeight parameters as well; click "Set Config" to try the effect of your changes.
- Under the "Storage" tab, enter the subject's initials into the "SubjectName" parameter.
- Switch to the "Source" tab; for the "ChannelNames" parameter enter electrode locations corresponding to amplifier channels as a white-space separated list (e.g., Fz CPz Cz CP3 ...).
- Click "Set Config".
- Instruct the subject as described in the section below.
- After reading the section on subject instructions below, click "Start."
- The recording will finish automatically. If you want to acquire more data, just click "Resume" as often as you like.
- Finally, click "Quit" to leave BCI2000.
Subject instruction
During the initial session, the subject's screen will either be blank, or displaying an arrow pointing up, down, left or right.
- When a left or right arrow is displayed, imagine movement of the respective hand. The imagined movement should be continuous opening and closing of the hand, similar to rotating a tennis ball in one's hand.
- When an up arrow is displayed, imagine simultaneous movement of both hands. This should be the same kind of movement as described for a single hand.
- When a down arrow is displayed, imagine movement of both feet. The movement should be similar to the one described for hands, i.e. imagine opening and closing your feet as if you could use them to grip an object.
- When you see a blank screen, please relax and stop any movement imagery.
Next Step
Analyzing the Initial Mu Rhythm Session shows you how to analyze data from the initial session in order to determine parameters for online feedback.