[Eeglablist] Some confusion about ERSPs/ITC precomputing

[诸梦妍]

Dear eeglablist,

I'm just computing EEG data using EEGLAB. However, I met some problems
about pre-computing ERSPs/ITC (channel measures) and hope someone could
help me.

In my experiment, I had 43 subjects, 500Hz sampling rate. It was a 2 by 2
repeated measures design, and each condition had about 30 trials and the
same 43 channels for each subject after rejecting. I pre-processed the raw
data in Brain Vision Analyzer until I extracted epochs for each
condition which was -200 to 800ms. I exported the epoched data to EEGLAB,
re-saved it as .set and .fdt files for each condition each subject, and
created a STUDY using those data. Then I just used the GUI and tried to
pre-compute the data.

For ERP part, it worked well and got the same result with Analyzer. But for
ERSPs/ITS part, it didn't. Actually, I do not quite understand the
parameters of ERSPs/ITC processing, so I just used the default. However, I
found that it only computed 23.4Hz to 250Hz's data, which do not include my
interest Frequency(3 to 30Hz). I tried to add options in GUI like "
'cycles',[3 0.5], 'nfreqs', 100, 'freqs',[3 30] ",but it turned out as a
wrong syntax.

When I used the default parameter, it showed in the MATLAB command window
like this below. I was just wondering what the red sentence means ( 1) to
4) ) and hope that someone could tell me what should I do if I just want it
to compute 3Hz to 30Hz frequency.

Computing Event-Related Spectral Perturbation (ERSP) and

  Inter-Trial Phase Coherence (ITC) images based on 31 trials

  of 500 frames sampled at 500 Hz.

Each trial contains samples from -200 ms before to

  798 ms after the timelocking event.

  Image frequency direction: normal

[?]1) Using 3 cycles at lowest frequency to 16 at highest.

[?]2) Generating 200 time points (-129.0 to 727.0 ms)

Finding closest points for time variableTime values for time/freq
decomposition is not perfectly uniformly distributed

[?]3) The window size used is 71 samples (142 ms) wide.

[?]4) Estimating 100 log-spaced frequencies from 23.4 Hz to 250.0 Hz.

Processing time point (of 200): 10 20 30 40 50 60 70 80 90 100 110 120

 130 140 150 160 170 180 190 200

Computing the mean baseline spectrum

Note: Add output variables to command line call in history to

      retrieve results and use the tftopo function to replot them


Thanks in advance,

Zhu Mengyan


-- 
Mengyan Zhu
Psychology department, Peking University
Dormitory 2061, Building 48,No.5 Yiheyuan Road, Haidian District, Beijing
100871, China
 E-mail: bj12116 at gmail.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sccn.ucsd.edu/pipermail/eeglablist/attachments/20120710/d3b469c2/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: B56.gif
Type: image/gif
Size: 385 bytes
Desc: not available
URL: <http://sccn.ucsd.edu/pipermail/eeglablist/attachments/20120710/d3b469c2/attachment.gif>