control signal in curosr movement application

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Yueqing Li
Posts: 51
Joined: 08 May 2007, 16:41

control signal in curosr movement application

Post by Yueqing Li » 21 Jan 2010, 16:51

Hello:

I have a question about the cursor movement application in BCI2000.

The tutorial said users could use the motor imagery to move the cursor up, while use relaxation to move it down. I am wondering whether they can use two different motor imageries to move the cursor up and down, respectively?

If that is possible, how can I configure the classifiers?

Thanks a lot.

jawilson
Posts: 109
Joined: 28 Feb 2005, 16:31

Post by jawilson » 25 Jan 2010, 09:27

Hello,
This is certainly straight-forward to do. Commonly, subjects will use foot imagery to move the cursor down. This control signal is measured from electrode Cz, using the mu/beta rhythms (the same as for hand movement). Therefore, you just need to add a row to the classifier that uses Cz, and the appropriate chosen bin. If you are following the tutorial, you want to use the output of the spatial filter, called CZ_OUT, so the classifier will have a new line that looks like:

CZ_OUT | 12Hz | 2 | 1

for the input channel, input element, output channel, and weight, respectively. The 12Hz value should be changed to whatever value you obtain from screening.

Let us know if you need additional information.
Adam

Yueqing Li
Posts: 51
Joined: 08 May 2007, 16:41

Post by Yueqing Li » 01 Feb 2010, 18:05

Hello:

Thank you very much, Adam. I have another question.

If I use two control signals for the two cursor movement, for example, up and down. How could the system know which control signal is for which cursor movement? I can't find any specification of the relation between them in the BCI2000 parameter configuration window.

By the way, it seems there are some difference in the weight of the input channel. The tutorial (http://www.bci2000.org/wiki/index.php/U ... e_Feedback) defined it as -1, but you specified it as 1. So, which one is correct? If they both work, what is the difference? Thanks.


Best


Yueqing

jawilson
Posts: 109
Joined: 28 Feb 2005, 16:31

Post by jawilson » 02 Feb 2010, 08:38

Yueqing Li wrote:Hello:

Thank you very much, Adam. I have another question.

If I use two control signals for the two cursor movement, for example, up and down. How could the system know which control signal is for which cursor movement? I can't find any specification of the relation between them in the BCI2000 parameter configuration window.

By the way, it seems there are some difference in the weight of the input channel. The tutorial (http://www.bci2000.org/wiki/index.php/U ... e_Feedback) defined it as -1, but you specified it as 1. So, which one is correct? If they both work, what is the difference? Thanks.


Best


Yueqing
1. For each direction of movement (e.g., vertical), there is only one control signal. It is calculated as the linear summation of the values in the Classifier matrix, and it uses the weights to determine if the cursor should move in the positive (up) or negative (down) direction. The output channel determines if the control signal should be in the horizontal (1), vertical (2), or depth (3) direction. So, if you have two rows in the Classifier matrix, each with the output channel set to 2 (vertical), and with weights of +1 and -1, then it is the sum of the power in the selected bins that is the vertical control signal. So, if the two rows have equal power, then the control signal will be 0, since they have opposite weights. If row 1 is greater (with a positive weight), it will move up, and if row 2 is greater, since it has a negative weight, it will move down.

2.The weight depends on which channel and frequency bin you are using. For example, right hand movement should move the cursor to the right. However, it is important to remember that if you are using the mu rhythm, then the power in the mu band DECREASES with motor imagery. Therefore, the weight for C3 should be -1 to move it right. Similarly, for C4 the weight should be C4.

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