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.
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.
Gathering System Specifications
To begin, you first need to gather some system data. For setup, this tutorial will assume that you will be using a dual-monitor setup as shown below, with the administrator of the sessions operating on monitor 1, and the volunteer will be watching monitor 2.
Open Display Properties by right-clicking on an empty portion of the desktop and clicking Properties, and navigating to the Settings tab.
|Make sure that Monitor 2, (which displays the instructions to the subject), is on the right of Monitor 1, (the experimenter's screen), and is aligned along the top.|
|What we need to make a note of is the width of monitor 1, and the width and height of monitor 2.|
|In this example we see that Monitor 1 is 2048 pixels wide, and monitor 2 is 1024 pixels wide by 768 pixels tall.|
Plug your adapter into the computer and turn it on.
Now we will determine what port your amplifier is connected to by going through Start → Settings → Control Panel → System → Hardware → Device Manager → Ports (COM & LPT). In this example, we see that the amplifier is connected to COM8.
Performing the Initial Session
- Start BCI2000 by double-clicking batch/StimulusPresentation_<YourAmplifier>.bat. For repeated use, placing a link to this file on the desktop might be a good idea.
- In the operator module, click "Config".
- In the configuration window, click "Load Parameters", and load the system-specific parameter file saved previously at parms/fragments/<YourSystem>.prm.
- Again, click "Load Parameters" to load parms/mu_tutorial/InitialMuSession.prm.
- 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.
- 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.
Instructions to the Subject
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 (e.g., squeezing a tennis ball) at a rate of about one opening/closing per second.
- 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 movements 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.
Analyzing the Initial Mu Rhythm Session shows you how to analyze data from the initial session in order to determine parameters for online feedback.