2008-02-13T20:01:48Z

Jfialkoff: /* Spatial Filtering */

==Spatial Filtering==
In the initial session you had a chance to gain some familiarity with the typical topography of a P300 signal. Generally, and as was likely the case for your own results, the P300 response is uniform over a large number of electrodes which implies that the spatial response has most of its energy in the lower frequencies. Mu responses, on the other hand, have a broader spatial response that includes more energy in mid and higher frequencies. Thus, with Mu responses, we will typically apply a spatial high-pass filter prior to performing an analysis. One example of such a filter is the common average reference (CAR) filter. Because this filter removes energy from the lower frequencies, however, it is generally a bad choice for P300 signals. For the purpose of this tutorial, we will show you how to configure BCI2000 so that no spatial filtering (i.e., identity spatial filtering) is applied to the signal.

===Creating an Identity Filter===
In its default configuration, BCI2000 requires the user to specify a spatial filter matrix. While there are spatial filters that may be effective for improving a P300 signal, we typically will not want to use a CAR filter. Instead we will specify a spatial filter that will not affect the signal (i.e., an identity spatial filter). For 8, 16 and 64 channel recordings, you may load appropriate parameter fragments are available at <tt>parms/fragments/spatial_filters/IdentityN.prm</tt> where <math>N</math> is the number of electrodes (e.g., 8, 16, 64). Applying one of these fragments will automatically set the appropriate values for the ''TransmitChList'' and ''SpatialFilter'' parameters. To set the spatial filter labels, please review the steps below. For other values of <math>N</math>, you will need to configure the ''TransmitChList'' and ''SpatialFilter'' parameters as follows:

*Go to the ''Source'' tab. In the ''TransmitChList'' parameter, enter a space-separated list of channel numbers beginning with 1: 1 2 3 4 ... N
*Go to the ''Filtering'' tab. Click the ''Edit Matrix'' button associated with the ''SpatialFilter'' parameter.
**Set both ''Number of columns'' and ''Number of rows'' to <math>N</math>, and click ''Set new matrix size''.
**In the diagonal entries of the matrix, enter the value 1.
**In the non-diagonal entries, enter the value 0.
**Set the matrix labels. This step is not mandatory. However, it makes subject-specific configuration easier to set up later on.
***Right-click the matrix, and choose ''Edit labels'' from the context menu.
***In the first column of each row (i.e., the row labels), enter the appropriate 10-20 electrode location corresponding to that channel.
**Close the matrix editor window.
*Click ''Configure Save'' in the configuration window, and check all parameter entries except ''TransmitChList'' and ''SpatialFilter''; close the window.
*Click ''Save Parameters'', and save your spatial filter configuration under <tt>parms/fragments/spatial_filters/Identity<YourMontage>.prm</tt>.
*Click ''Configure Save'' again, uncheck all parameter entries and close the window.

Template:Tutorial Spatial Filter

2008-02-13T19:59:15Z

Jfialkoff: /* Spatial Filtering */

==Spatial Filtering==
In the initial session you had a chance to gain some familiarity with the typical topography of a P300 signal. Generally, and as was likely the case for your own results, the P300 response is uniform over a large number of electrodes which implies that the spatial response has most of its energy in the lower frequencies. Mu responses, on the other hand, have a broader spatial response that includes more energy in mid and higher frequencies. Thus, with these types of responses, we will typically apply a spatial high-pass filter prior to performing an analysis. One example of such a filter is the common average reference (CAR) filter. Because this filter removes energy from the lower frequencies, however, it is generally a bad choice for P300 signals. For the purpose of this tutorial, we will show you how to configure BCI2000 so that no spatial filtering (i.e., identity spatial filtering) is applied to the signal.

As a result of the initial session, you have some idea of the signal topography, and spatial filtering that extracts the signal best.
In this tutorial, we use ''Common Average Reference (CAR)'' filtering because it gives generally good results, and has the advantage of being independent of the montage used. Also, this method is independent of subject specific parameters, so you will only need to configure it once for a given electrode montage.

===Creating an Identity Filter===
In its default configuration, BCI2000 requires the user to specify a spatial filter matrix. While there are spatial filters that may be effective for improving a P300 signal, we typically will not want to use a CAR filter. Instead we will specify a spatial filter that will not affect the signal (i.e., an identity spatial filter). For 8, 16 and 64 channel recordings, you may load appropriate parameter fragments are available at <tt>parms/fragments/spatial_filters/IdentityN.prm</tt> where <math>N</math> is the number of electrodes (e.g., 8, 16, 64). Applying one of these fragments will automatically set the appropriate values for the ''TransmitChList'' and ''SpatialFilter'' parameters. To set the spatial filter labels, please review the steps below. For other values of <math>N</math>, you will need to configure the ''TransmitChList'' and ''SpatialFilter'' parameters as follows:

*Go to the ''Source'' tab. In the ''TransmitChList'' parameter, enter a space-separated list of channel numbers beginning with 1: 1 2 3 4 ... N
*Go to the ''Filtering'' tab. Click the ''Edit Matrix'' button associated with the ''SpatialFilter'' parameter.
**Set both ''Number of columns'' and ''Number of rows'' to <math>N</math>, and click ''Set new matrix size''.
**In the diagonal entries of the matrix, enter the value 1.
**In the non-diagonal entries, enter the value 0.
**Set the matrix labels. This step is not mandatory. However, it makes subject-specific configuration easier to set up later on.
***Right-click the matrix, and choose ''Edit labels'' from the context menu.
***In the first column of each row (i.e., the row labels), enter the appropriate 10-20 electrode location corresponding to that channel.
**Close the matrix editor window.
*Click ''Configure Save'' in the configuration window, and check all parameter entries except ''TransmitChList'' and ''SpatialFilter''; close the window.
*Click ''Save Parameters'', and save your spatial filter configuration under <tt>parms/fragments/spatial_filters/Identity<YourMontage>.prm</tt>.
*Click ''Configure Save'' again, uncheck all parameter entries and close the window.

Template:Tutorial Spatial Filter

2008-02-13T19:58:43Z

Jfialkoff:

==Spatial Filtering==
In the initial session you had a chance to gain some familiarity with the typical topography of a P300 signal. Generally, and as was likely the case for your own results, the P300 response is uniform over a large number of electrodes which implies that the spatial response has most of its energy in the lower frequencies. Mu responses, on the other hand, have a broader spatial response that includes more energy in mid and higher frequencies. Thus, with these types of responses, we will typically apply a spatial high-pass filter prior to performing an analysis. One example of such a filter is the common average reference (CAR) filter. Because this filter removes energy from the lower frequencies, however, it is generally a bad choice for P300 signals. For the purpose of this tutorial, we will show you how to configure BCI2000 so that no spatial filtering (i.e., identity spatial filtering) is applied to the signal.

As a result of the initial session, you have some idea of the signal topography, and spatial filtering that extracts the signal best.
In this tutorial, we use ''Common Average Reference (CAR)'' filtering because it gives generally good results, and has the advantage of being independent of the montage used. Also, this method is independent of subject specific parameters, so you will only need to configure it once for a given electrode montage.
===Creating an Identity Filter===
In its default configuration, BCI2000 requires the user to specify a spatial filter matrix. While there are spatial filters that may be effective for improving a P300 signal, we typically will not want to use a CAR filter. Instead we will specify a spatial filter that will not affect the signal (i.e., an identity spatial filter). For 8, 16 and 64 channel recordings, you may load appropriate parameter fragments are available at <tt>parms/fragments/spatial_filters/IdentityN.prm</tt> where <math>N</math> is the number of electrodes (e.g., 8, 16, 64). Applying one of these fragments will automatically set the appropriate values for the ''TransmitChList'' and ''SpatialFilter'' parameters. To set the spatial filter labels, please review the steps below. For other values of <math>N</math>, you will need to configure the ''TransmitChList'' and ''SpatialFilter'' parameters as follows:

*Go to the ''Source'' tab. In the ''TransmitChList'' parameter, enter a space-separated list of channel numbers beginning with 1: 1 2 3 4 ... N
*Go to the ''Filtering'' tab. Click the ''Edit Matrix'' button associated with the ''SpatialFilter'' parameter.
**Set both ''Number of columns'' and ''Number of rows'' to <math>N</math>, and click ''Set new matrix size''.
**In the diagonal entries of the matrix, enter the value 1.
**In the non-diagonal entries, enter the value 0.
**Set the matrix labels. This step is not mandatory. However, it makes subject-specific configuration easier to set up later on.
***Right-click the matrix, and choose ''Edit labels'' from the context menu.
***In the first column of each row (i.e., the row labels), enter the appropriate 10-20 electrode location corresponding to that channel.
**Close the matrix editor window.
*Click ''Configure Save'' in the configuration window, and check all parameter entries except ''TransmitChList'' and ''SpatialFilter''; close the window.
*Click ''Save Parameters'', and save your spatial filter configuration under <tt>parms/fragments/spatial_filters/Identity<YourMontage>.prm</tt>.
*Click ''Configure Save'' again, uncheck all parameter entries and close the window.