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Dear Jeff and Jim,<br>
<br>
another possibility is that the events in your analog file are not
perfectly encoded: there might be several values in the leading edge
transition events. By default, EEGLAB will import one event per value.
The solution to this problem is to import the BDF file without a
channel event and without a reference (if you specify a reference and
no channel event, the channel event will be re-referenced). Then go to
menu item File > Import event info > From data channel. Enter
your channel index, and select "3" instead of "1" for the leading edge
transition maximal length. This will place the leading/trailing edge on
the first/last data point where a transition is detected (it will
assign the value for the type at the plateau). It might solve your
problem. You may prevent the function from erasing the data channel (by
clicking on the appropriate checkbox) and visualize the data channel
along with the extracted events by typing on the command line<br>
<br>
>> eegplot(EEG.data(end,:), 'events', EEG.event);<br>
<br>
Finally, do not forget to re-reference your data (otherwise there is a
40dB loss in signal/noise).<br>
<br>
Arno<br>
<br>
ps: with some BIOSEMI files, you will also have to enter
"bitand(uint32(X), 255)" in the "preprocessing transform" edit box of
the GUI called by the menu item "File > Import event info > From
data channel"<br>
<br>
Jeff Johnson wrote:<br>
<blockquote type="cite"
cite="mid5.2.1.1.2.20050215130700.00c4f0a8@pop.uci.edu">We frequently
have this problem too, and we figure that it has something to do with
either pausing/unpausing or clicking the mouse in Biosemi's acquisition
program (in Labview). One way around it (although we haven't tried)
might be to pause/unpause the acquisition by sending a byte (244 or
245?) from your stimulus computer, instead of using the mouse.
<br>
<br>
To get around it in EEGLAB, we usually just epoch our data around the
events that have a particular value. For example:
<br>
<br>
pop_epoch( EEG, {'[1621761]'}, [-0.100 2.000] );
<br>
<br>
Our events of interest always have a value of 1621761, whereas the
extraneous events have different values. You can easily find your event
values by using the pull-down menu in EEGLAB (edit >> event
values, I think). As you note, there are probably many other ways
around this problem, but this method works about 99% of the time for
us.
<br>
<br>
Jeff
<br>
<br>
At 09:14 PM 2/14/2005 -0700, Jim Kroger wrote:
<br>
<blockquote type="cite">Hello, I am wondering if anybody else has
experienced this problem. We use a Biosemi 128-channel.
<br>
Channel 129 has event markers.
<br>
<br>
When using this channel to mark event times in EEGLAB, we have some
kind of ring or artifact that causes EEGLAB to mark two events instead
of one. We also try loading this into EMSE, and do not have the
problem.
<br>
<br>
We're having a bit of trouble understanding why this happens. Although
we can imagine ways to program around the problem, it would be best if
we understood it.
<br>
<br>
Many thanks for any pointers.
<br>
<br>
Jim
<br>
<br>
<br>
<br>
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</blockquote>
<br>
<br>
<div class="moz-signature">-- <br>
<br>
<b><font face="Arial,Helvetica"><font size="+1">Arnaud Delorme, Ph.D.</font></font></b>
<br>
<font face="Arial,Helvetica"><font size="+1"><font color="#3333ff">Swartz
Center for Computational Neuroscience,</font> <font color="#3333ff">INC,
University of San Diego California</font></font></font>
<br>
La Jolla, CA92093-0961, USA
<p><font face="Arial,Helvetica"><b>Tel</b> :<i>(+1)-858-458-1927 ext 15</i></font>
<br>
<font face="Arial,Helvetica"><b>Fax</b> :<i>(+1)-858-458-1847</i></font>
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href="http://www.sccn.ucsd.edu/%7Earno">sccn.ucsd.edu/~arno</a></font>
<br>
<font face="Arial,Helvetica"><b>To think upon</b>:</font></p>
<blockquote><dt><font face="Arial,Helvetica"> Life is not a problem to
be solved but a reality to be experienced.
<font size="-5"><br>
<br>
</font></font></dt>
<dd><font face="Arial,Helvetica"><i>Siren Kierkegaard</i></font></dd>
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