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. 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.
- Start BCI2000 by double-clicking batch/StimulusPresentation_screening_<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 parameters/fragments/parms/fragment_<YourAmplifier>.prm and parameters/fragments/parms/Mu_screening.prm
- In the Storage tab:
- Set SubjectName to the volunteer’s initials.
- Set SubjectSession to 001
- Set SubjectRun to 01
- Please note that the data will be stored into a directory dedicated to the screening data.
In the Source tab, set:
- SourceCh to 8
- This tells the program that only 8 channels will be sending data
- ChannelNames to F3 F4 T7 C3 Cz C4 T8 Pz
- This names the channels to the electrode positions they report
- SourceChOffset to 0 0 0 0 0 0 0 0
- This tells the program that none of the channels have an offset
- SourceChGain to 0.019 0.019 0.019 0.019 0.019 0.019 0.019 0.019
- This is the conversion for each channel for A/D information into microvolts
- COM port to the port name that you found earlier
- In this example we would put in COM8:
- NotchFilter to disable
- We will use this to identify any poorly-gelled electrodes
- AlignChannels to 0
- This makes sure that the electrodes, which gather data simultaneously, will be treated as such.
- TransmitChList to F3 F4 T7 C3 Cz C4 T8 Pz
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 plus one
- In our example, this would be 2049
- This shifts the character display to the right 2049 pixels, making it display on the secondary monitor
- Take note of the Sequence field:
- This field calls for four single-digit numbers separated by one space. Initially it will be 1 1 1 1.
- These numbers are the relative frequency 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.
- 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
Each run gathers 20 data points that differentiate between moving the left hand, the right hand, both hands, and both feet. Ideally, there should be 100 points of data, 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 points 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.