[Eeglablist] Some confusion about ERSPs/ITC precomputing

Wed Jul 11 11:22:58 PDT 2012

Dear PengMin,

> How could I get the results with frequency in the following way: 3 6 9 12
15 18 ......45? Thanks a lots!

'freqs', [3 45], 'nfreqs', 14

The second options specifies the resolution of your frequency range. In the
example above, 3-45 Hz will be divided by 14, which is (45-3)/14 = 3
(assuming you use the default freqscale option). You can fine-tune the
parameter by cut-and-try then if necessary.

Makoto

2012/7/10 PengMin Qin <qin.pengmin at gmail.com>

> Dear all,
>
> Thank you very much! Your talk is very useful.
>
> I have a similar question. I make a study file, and  then then use the
> precompute channel measure to calculate the ERSP and ITC. In this study
> file including 22 participants, each participants have two conditions. The
> epoch for each condition is 1100 ms (-200 to 900). when I calculate the
> ERSP and ITC, I use three kinds of parameters for cycles: [1 0], [1 1] and
> [1 0.5]; frequency [3 45], baseline [0].  When I check the results of these
> three analysis, the frequency of the results are same: 3.00    3.93
> 5.15   6.76    8.86    11.61   15.23    19.97    26.18    34.32   45.00. Is
> this right? How could I get the results with frequency in the following
> way: 3 6 9 12 15 18 ......45? Thanks a lots!
>
> Best,
> Pengmin
>
>
>
> 2012/7/10 Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
>
>> Dear Mengyan,
>>
>> If you want to have 3 Hz to 30 Hz range after wavelet transform, the
>> problem is that you have only -200 to 800 ms so that it is extremely
>> difficult to have 3 Hz.
>>
>> If you use 3 cycles at 3 Hz, your window side is (1000ms/3Hz)*3cycles =
>> 1000ms, meaning that 1000ms length data generates 1 datapoint after wavelet
>> transform. So your epoch can allow to generate only 1 datapoint!
>>
>> You can either
>>
>> 1. prepare longer epoch (from -1000 ms to 2000 ms relative to stimulus
>> onset) and use 3 Hz 3 cycle at the lowest: then you'll have -500 to 1500 ms
>> after wavelet transform. You lose 500 ms from both sides of your epoch,
>> because your window side is 1000 ms. It does not matter very much if your
>> epoch overlaps each other if it is not too much.
>>
>> 2. Give up the lowest frequency range of 3 Hz and use 5 Hz instead with 2
>> cycles (decreasing the cycle number reduces sensitivity though). Then
>> you'll have 0 to 800 ms after wavelet transform. You lose 200 ms from both
>> sides of your epoch since your window size is (1000ms/5Hz)*2cycles = 400ms.
>>
>> You can try No.2 immediately. Use the following options to see what
>> happens.
>>
>> 'cycles', [2 0.5], 'freqs', [5 30], 'nfreqs', 50
>>
>> Makoto
>>
>>
>>
>> 2012/7/9 诸梦妍 <bj12116 at gmail.com>
>>
>>>  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
>>>
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>>
>>
>>
>> --
>> Makoto Miyakoshi
>> JSPS Postdoctral Fellow for Research Abroad
>> Swartz Center for Computational Neuroscience
>> Institute for Neural Computation, University of California San Diego
>>
>>
>> _______________________________________________
>> Eeglablist page: http://sccn.ucsd.edu/eeglab/eeglabmail.html
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>
>

-- 
Makoto Miyakoshi
JSPS Postdoctral Fellow for Research Abroad
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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