Yes, these are just a naming convention that you use to tag events in the data where you know something about the state that the subject is in (e.g., based on the stimulus that you presented or perhaps the response buttons that the subject pressed). <br>
The standard approach to get meaningful markers into your recording is to design an experiment using ePrime, Presentation or, e.g., the MATLAB Psych toolbox, in which the subject is put in a particular cognitive state at various times (e.g. instructed to imagine a left-hand movement in some trials and to imagine a right-hand movement during other trials). When the subject runs through the experiment, it is the responsibility of the experiment program to emit event markers that are then recorded together with the EEG (the mechanism usually depends on the amplifier and/or recording program -- e.g., some have a Parallel Port interface, others have a serial port, others have analog trigger inputs). As long as an appropriate mechanism for the respective amplifier was used, the events (including their type and their latencies) will be stored as part of the recording and EEGLAB will attempt to read them and store them in EEG.event automatically. <br>
<br>In case of the BCI competition data, the data is stored in a custom MATLAB-compatible format, and the events are, I think, stored in an array called "mrk" (including their types and their latencies). These are the ones that you would use to build your EEG data set. Because the event types are numbers in the competition data while EEGLAB prefers to work with strings, you will need to translate the numbers to strings (e.g., using num2str) before you run set_new as below.<br>
<br>Best,<br>Christian<br><br><div class="gmail_quote">2011/9/29 Mehdi Karamnejad <span dir="ltr"><<a href="mailto:mehdi.karamnejad@srttu.edu">mehdi.karamnejad@srttu.edu</a>></span><br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div dir="ltr">Thanks for the reply, using the points in <a href="http://sccn.ucsd.edu/wiki/A02:_Importing_Event_Epoch_Info" target="_blank">this</a> page, there is a little description about event types:<br><br><blockquote style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;" class="gmail_quote">
...the channel is an event channel with values 1 (stimulus onset), 2 (subject response), and 0 (other)....<br></blockquote>I'm not really sure what these are. is 1 , 2 or 0 just a naming convention? so they could be anything as long as they are consistently named through the whole process using EEGLAB and BCILAB? from what I've figured out in <a href="http://sccn.ucsd.edu/wiki/A02:_Importing_Event_Epoch_Info" target="_blank">this</a> page , for each "time X channel" entry there should be an event type.now I have no idea what kind of event it would be for each of entries in my dataset? 1,2 or 0?<br>
Another question is about latencies, how can I obtain latencies for my events? <br><div class="im">-----------<br>Regards, Mehdi Karamnejad<br>Rajaee Artificial Intelligence & Robotics Laboratory , Shahid Rajee University<br>
<br></div><div><div></div><div class="h5"><div class="gmail_quote">
On Fri, Jun 17, 2011 at 12:50 AM, Christian Kothe <span dir="ltr"><<a href="mailto:christiankothe@googlemail.com" target="_blank">christiankothe@googlemail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
Hello Mehdi,<br><br>yes, importing the format of the BCI competition into an EEGLAB-compatible format with appropriate markers requires quite some special treatment. On our wiki we have a piece of code which demonstrates loading & running a simple CSP approach over it using just bare-bones MATLAB: <a href="http://sccn.ucsd.edu/wiki/Minimalist_BCI" target="_blank">http://sccn.ucsd.edu/wiki/Minimalist_BCI</a> This should give you an idea of how the data is laid out (this is for the .mat version of one of the data sets - I hope it's the data set that you are interested in). You may also check whether this code runs for you right out of the box.<br>
<br>To generate from this an EEGLAB-compatible data set, you might want to take a look at the wiki page on the data structure layout: <a href="http://sccn.ucsd.edu/wiki/A05:_Data_Structures" target="_blank">http://sccn.ucsd.edu/wiki/A05:_Data_Structures</a>. A bit more conveniently is BCILAB's function set_new, which is used like in the following usage example:<br>
<br>If you have extracted the following variables from the BCI competition data set:<br><span style="font-family: courier new,monospace;">mydata</span> (numeric array of #channels x #samples)<br><span style="font-family: courier new,monospace;">mysrate</span> (sampling rate in Hz)<br>
<span style="font-family: courier new,monospace;">mychannels</span> (cell array of channel names, e.g. {'C3', 'C4', 'Cz', ...})<br><span style="font-family: courier new,monospace;">myeventtypes</span> (cell array of event type strings -- note: these should be strings, e.g. {'1', '2', '1', '2' ...}, not numbers)<br>
<span style="font-family: courier new,monospace;">myeventlatencies</span> (cell array of event latencies, measured in samples, e.g. {10200, 20300, 55100, ...})<br><br>Then you can create a new set using the command.<br><span style="font-family: courier new,monospace;">traindata = exp_eval(set_new('data',mydata, 'srate',mysrate, 'chanlocs',struct('labels',mychannels), 'event',struct('type',myeventtypes,'latency',myeventlatencies)));</span><br>
<br>If you save the data set now as a .set file using <br><br><span style="font-family: courier new,monospace;">pop_saveset(traindata</span>)<br><br>... then you can then use it with BCILAB following the GUI tutorials. For this to work, you need to remember that you named your event
types a certain way when you created the EEGLAB set, and BCILAB
needs to know what events it should use. The tutorial data sets use
different event types than those that you have, so assuming that you used the strings '1' and '2', you need to pass {'1','2'} instead of the {'S 1', 'S 2'} in the GUI dialog box where the marker names are specified.<br>
<br><br>Likewise, when you want to go through the scripting tutorials with it (say: tutorial_erd1.m or tutorial_erd2.m), you first need to replace the respective io_loadset line which loads the file (you can also directly use the traindata that you have in your workspace),<br>
and replace the names of the event types that are declared to BCILAB. In tutorial_erd1.m, for example, the line<br><br><span style="font-family: courier new,monospace;">myapproach = {'CSP' 'SignalProcessing',{'EpochExtraction',{'TimeWindow',[0 3.5],'EventTypes',{'StimulusCode_2','StimulusCode_3'}}}};</span><br>
<br>needs to be changed to <br><br><span style="font-family: courier new,monospace;">myapproach = {'CSP'
'SignalProcessing',{'EpochExtraction',{'TimeWindow',[0
3.5],'EventTypes',{'1','2'}}}};<br><br><span style="font-family: arial,helvetica,sans-serif;">... and you should be ready to go (again assuming that you actually named your markers '1' and '2'). If you want to use the more advanced approaches, you need to adapt the event types there, too.<br>
<br>Best,<br>Christian<br><br>PS: I'm actually planning to write a tutorial for BCI competition data sets at some point, but didn't yet get to it.<br></span></span><br><div class="gmail_quote"><div><div></div><div>
2011/6/16 Mehdi Karamnejad <span dir="ltr"><<a href="mailto:mehdi.karamnejad@srttu.edu" target="_blank">mehdi.karamnejad@srttu.edu</a>></span><br>
</div></div><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div><div></div><div><div dir="ltr"><div dir="ltr">Hello,<br><br>I'm trying to deploy some approaches of BCILAB on BCI competition IV dataset 1 (<a href="http://www.bbci.de/competition/iv/desc_1.html" target="_blank">here</a> is the link to description of this dataset)<br>
I take the following steps:<br><ol><li>cnt matrix contains raw continues EEG data in volts and I first convert the values to micro volts . cnt matrix also arranges data <font face="sans-serif">in the form of time x channels so I take the transpose of the matrix to produce a matrix in the form of channels x time</font></li>
<li><font face="sans-serif">for testing reasons and making processes much less time-consuming , I just extracted a small portion of the signal to import into EEGLAB</font></li><li><font face="sans-serif">then I imported the extracted signal into EEGLAB along with it's channel location</font></li>
<li><font face="sans-serif">then I had to create the Events because BCILAB needs it, I did this using File>> Import event info >> >From data channel and picked 59 as my event channel and left other options as default since I'm not sure what they do yet.<br>
** 59 is the number of entire channels . I'm not sure what my events are although I've read the EEGLAB wiki, <b>could someone tell me what are experimental events in EEG signals? and how can I figure out which channel(s) are the event channels?<br>
</b></font></li><li><font face="sans-serif">then I saved all of my work as an EEGLAB dataset and loaded it into BCILAB and created a new CSP approach. when modifying the approach I don't know what to fill in for "Epoch time window relative to the events" and "Event marker types for which epochs shall be extracted " . for the second one I have read a tutorial which 's 1''s 2' is </font><font face="sans-serif">filled in </font><font face="sans-serif">but I don't really understand what this means and when I try to train my model I get an error with these settings.<br>
<b>could you please explain to me what </b></font><b><font face="sans-serif"> "Event marker types for which epochs shall be extracted " is?</font></b><font face="sans-serif"></font></li></ol>and could you tell me what do I generally need to do to make my dataset appropriate for loading into BCILAB? (for now appropriate enough to use the CSP approach )<br>
-----------<br>Regards, Mehdi Karamnejad<br>Rajaee Artificial Intelligence & Robotics Laboratory , Shahid Rajee University<br><br>
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