daten uploaded!

Muthuraman Muthuraman muthuraman10 at HOTMAIL.COM
Wed Jan 10 17:44:25 CET 2007


discard my question regarding uploading the data in my previous mail
I have uploaded the file in
and this is the link

thanking you

with regards

>From: Robert Oostenveld <r.oostenveld at FCDONDERS.RU.NL>
>Reply-To: FieldTrip discussion list <FIELDTRIP at NIC.SURFNET.NL>
>Subject: Re: [FIELDTRIP] Coherence!
>Date: Tue, 9 Jan 2007 17:53:23 +0100
>dear Muthuraman
>On 9 Jan 2007, at 11:08, Muthuraman Muthuraman wrote:
>>    = channelselection({'all' 'M1'}, data.label);
>>cfg.channelcmb = channelcombination({'all' 'M1'}, data.label);
>for DICS you will also need the cross-spectrum between all EEG  channels.
>Hence you should do cfg.channelcmb = 'all'. The code above  is fine if you
>want to look at coherence on channel level, which is  what you currently
>are looking at.
>>cfg.foilim     = [2 30];
>>cfg.taper      = 'hanning';
>>cfg.pad        = 1;
>>cfg.keeptrials = 'yes';
>>cfg.variance   = 'yes';
>>cfg.jackknife  = 'yes';
>>freqmtmfft     = freqanalysis(cfg, data);
>>fdmtmfft       = freqdescriptives([], freqmtmfft);
>This uses 1 hanning taper, and you have one-second long data  segments.
>Hence the frequency resolution is 1/1s = 1Hz.
>>cfg.method     = 'mtmwelch';
>>cfg.output     = 'powandcsd';
>>cfg.foi        = [2:2:30];
>>cfg.t_ftimwin  = ones(1,length(cfg.foi)).*0.5;
>>cfg.taper      = 'hanning';
>>cfg.pad        = 1;
>This uses a 500ms window per trial to do the estimation. That gives  you a
>1/0.5 = 2Hz frequency resolution. The lower frequency  resolution implies
>that there is more frequency smoothing, so the  estimate will be different.
>If the true coherence peak is broad-band  (i.e. broader than 1 Hz), then
>the estimate will probably be better  (=higher), if not, then it will be
>worse (=lower).
>>cfg.keeptrials = 'yes';
>>cfg.variance   = 'yes';
>>cfg.jackknife  = 'yes';
>>freqmtmwelch   = freqanalysis(cfg, data);
>>fdmtmwelch     = freqdescriptives([], freqmtmwelch);
>You probably should do
>   cfg = []
>   cfg.variance   = 'yes';
>   cfg.jackknife  = 'yes';
>and then
>   fdmtmwelch     = freqdescriptives(cfg, freqmtmwelch);
>since the variance options do not apply to freqanalysis, but to
>freqdescriptives instead.
>>I have attached a figure with this mail[Coherence between C3 and  M1] in
>>which there is a difference in coherence values
>>for the fieldtrip method and the welch periodogram method with and
>>without laplacian transform
>>Is there any input parameters i can change in the fieldtrip analysis
>>so that i can have the similar values, or is there any major  differences
>>in the methods
>>with fieldtrip and Welch periodogram method.
>There is a difference in scalp-current-density (laplacian) data and  EEG
>potential data, so I also expect coherence to be different. It is  better
>to report channel level CSD/laplacian coherence than channel- level
>ordinary potential difference, since SCD/laplacian is reference  free and
>potential is not. Note that you can also use FT to compute  coherence on
>SCD data, assuming that you can export the laplacian  data to a raw file. I
>don't know which software you used to compute  the SCD/laplacian and welsh
>coherence that you have in the figure,  therefore I also cannot comment on
>why the values are different. The  difference between the mtmfft and
>mtmwelsh can be explained (see  above) because the different frequency
>best regards,

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