[Eeglablist] How to save the normalized data that we see in scroll data display?

[Tim Mullen]

Yes, temporal z-normalization will generally change the voltage topography,
since each electrode's mean voltage (DC offset) is removed and each
electrode's voltage has been independently rescaled by a different
quantity.

Note that we are not describing *spatial* z-normalization, which, for a
given time point, is equivalent to performing a common average reference
(subtracting spatial mean from each electrode) followed by rescaling all
electrodes by the same quantity (spatial stdev). This will preserve
relative voltage between pairs of electrodes within a constant factor
(pairwise voltage difference is also rescaled by the spatial stdev) -- and,
if data is already CAR, does not affect pairwise voltage ratios.

In any case, I can't see why one would want to temporally normalize before
plotting voltage maps.

Tim


On Wed, Nov 7, 2012 at 3:01 PM, Iman M.Rezazadeh <irezazadeh at ucdavis.edu>wrote:

> Hi,****
>
> ** **
>
> So, I have one question here:****
>
> If you normalize the data using zscore , then at each time point the
> topography of original data and normalized one will be different since for
> topo map the voltage of adjacent electrodes are also important? ****
>
> Could you please clarify more …****
>
> ** **
>
> Best,****
>
> Iman****
>
> ** **
>
> Iman M.Rezazadeh, PhD****
>
> Postdoctoral Research Fellow****
>
> Center for Mind and Brain****
>
> University of California, Davis****
>
> irezazadeh at ucdavis.edu****
>
> Cell:310-490-1808****
>
> Skype: Imanmr****
>
> ** **
>
> ** **
>
> *From:* eeglablist-bounces at sccn.ucsd.edu [mailto:
> eeglablist-bounces at sccn.ucsd.edu] *On Behalf Of *Edward Justin Modestino
> *Sent:* Tuesday, November 06, 2012 6:50 AM
> *To:* Tim Mullen
> *Cc:* EEGLAB List
> *Subject:* Re: [Eeglablist] How to save the normalized data that we see
> in scroll data display?****
>
> ** **
>
> Yes, this code works:
> *normdata = zscore(EEG.data,0,2);
> EEG.data = normdata;*****
>
> On Mon, Nov 5, 2012 at 9:07 PM, Tim Mullen <mullen.tim at gmail.com> wrote:**
> **
>
> As I posted earlier, it's simple to compute:****
>
> ** **
>
> normdata = zscore(EEG.data,0,2);****
>
> ** **
>
> No need to reshape, etc. This will normalize each channel and each epoch
> independently.****
>
> ** **
>
> Tim****
>
> ** **
>
> On Fri, Nov 2, 2012 at 11:23 AM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
> wrote:****
>
> Dear Edward,
>
> > Error: Expression or statement is incorrect--possibly unbalanced (, {,
> or [.
>
> Oops. The line must be****
>
>
> tmp = reshape(EEG.data, [size(EEG.data, 1) size(EEG.data, 2) *****
>
> size(EEG.data, 3) ]);
>
> The last parenthesis was missing.
> By the way I learned a shortcut for it yesterday, and
>
> tmp = EEG.data(:,:);
>
> should also work.
>
> Makoto
>
>
> 2012/11/2 Edward Justin Modestino <edward.modestino at gmail.com>:
> > Makoto,
> > I need to be able to get this working as well. I tried it and got the
> > following error.****
>
> >
> >
> >>> tmp = reshape(EEG.data, [size(EEG.data, 1) size(EEG.data, 2) *
> > size(EEG.data, 3) ];
> > tmp = zscore(tmp, 0, 2);
> > tmp = reshape(tmp, size(EEG.data));
> > EEG.data = tmp;****
>
> > ??? tmp = reshape(EEG.data, [size(EEG.data, 1) size(EEG.data, 2) *
> >                                                                   |
> > Error: Expression or statement is incorrect--possibly unbalanced (, {,
> or [.****
>
> >
> >
> > On Thu, Nov 1, 2012 at 1:21 PM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
> > wrote:
> >>
> >> Dear nabaraj,
> >>
> >> Check out the function zscore.
> >> If your data are epoched, then the code should be something like
> >>
> >> tmp = reshape(EEG.data, [size(EEG.data, 1) size(EEG.data, 2) *
> >> size(EEG.data, 3) ];
> >> tmp = zscore(tmp, 0, 2);
> >> tmp = reshape(tmp, size(EEG.data));
> >> EEG.data = tmp;
> >>
> >> This should normalizes each channel.
> >>
> >> Makoto
> >>
> >> 2012/10/29 nabaraj dahal <nabarajdahal at gmail.com>:
> >> > Dear list member,
> >> > I wish to save the normalized data of all channels for further
> >> > processing.
> >> > Is there any way I can save the normalized data of all channels that
> we
> >> > see
> >> > in scroll data display?
> >> > I would be grateful for you help.
> >> >
> >> > Best Regards,
> >> > Nab
> >> >
> >> > _______________________________________________
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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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> >> eeglablist-request at sccn.ucsd.edu
> >
> >
> >
>
>
> --
> 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
> To unsubscribe, send an empty email to
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> eeglablist-request at sccn.ucsd.edu****
>
> ** **
>
>
>
> ****
>
> ** **
>
> -- ****
>
> ---------  αντίληψη -----------****
>
>
>
>
> --
> Edward Justin Modestino, Ph.D.
> Neuroscientist/Faculty
> Atlantic University****
>



-- 
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