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.
Preparing for the Initial (Screening) Session
To begin, you first need to gather some system data. This tutorial will assume that you will be using a dual-monitor setup as shown below, with the experimenter of the sessions operating on monitor 1, and the subject 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.|
Connect your amplifier to the computer, and turn it on.
If your amplifier is from the gMOBIlab family, you will need to make a note of the port it is connected to. In order to determine that port, in Windows XP, go to the Windows Start Menu, and choose Start → Control Panel → System → Hardware → Device Manager → Ports (COM & LPT). Different versions of Windows may have the Device Manager in a different location. In this example, we see that the amplifier is connected to COM8.
You can now close all open windows.
- When you are using a source module that is not part of the BCI2000 core distribution, you will need to create a batch file and parameter file for your amplifier first. Please follow the steps described on this page.
- 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.
- Click Load Parameters, and load parms/mu_tutorial/InitialMuSession.prm. Then, load parms/fragments/amplifiers/<YourAmplifier>.prm.
- In the Storage tab:
- Set SubjectName to the subject’s initials.
- Set SubjectSession to 001
- Set SubjectRun to 01
In the Source tab, set:
- ChannelNames to the electrode positions according to the 10-20 convention.
- This names the channels according to their respective electrode positions.
- In our example, F3 F4 T7 C3 Cz C4 T8 Pz has been entered.
- TransmitChList to the channel names entered into the ChannelNames parameter
- If using a gMOBIlab amplifier, set COM port to the port name that you found earlier.
- In this example, we would put in COM8:
In the Application tab, set:
- WindowWidth to the width of the display monitor, found earlier.
- WindowHeight to the height of the display monitor, found earlier.
- In our example, WindowWidth would be set to 1024 and WindowHeight would be set to 768.
- WindowLeft to the width of the experimenter’s monitor.
- In our example, this would be 2048.
- This shifts the character display to the right 2048 pixels, making it display on the secondary monitor.
- Take note of the Sequence field:
- This field contains four single-digit numbers separated by one space. Initially it will be 1 1 1 1.
- These numbers are frequencies of calling for the different subject activity. The first number corresponds to the left hand, the second is the right hand, the third for both hands, the fourth for both feet.
- Therefore, setting this field to 2 1 0 1 will call for the subject to move the left hand twice as often as the right or both feet, and will never call for both hands to be moved.
- Finally, save the parameter file where you deem appropriate.
- Click Set Config.
- Instruct the subject as described in the section below.
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.
Performing the Initial Session
To start an experimental run, click Run in the operator window. Each run gathers 20 data points, or "trials", that differentiate between moving the left hand, the right hand, both hands, and both feet. Ideally, there should be 100 trials, meaning that five runs are suggested. This is done as five separate runs instead of one to allow the subject a chance between each run to rest, blink, swallow, speak, or have some water if so desired.
Once all data have been collected, the Analyzing the Initial Mu Rhythm Session page shows you how to analyze data from the initial session in order to determine parameters for online feedback.