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

Wed Nov 7 23:23:07 PST 2012

Thanks Tim! 

So, you are saying we should plot topomap before normalization using zscore
for each channel.

The reason behind my question is different subjects have different scalp and
skull thickness which effects on the magnitude of EEG at electrode level.
When one would want to do grand averaging over subjects this issue may cause
a problem in averaging ( a subject with thinner  scalp thickness has more
share on the grand average data)

Any thought? 

Best,

Iman

From: Tim Mullen [mailto:mullen.tim at gmail.com] 
Sent: Wednesday, November 07, 2012 11:10 PM
To: Iman M.Rezazadeh
Cc: Edward Justin Modestino; EEGLAB List
Subject: Re: [Eeglablist] How to save the normalized data that we see in
scroll data display?

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
>> >
>> > _______________________________________________
>> > 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
>> _______________________________________________
>> 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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-- 

---------  αντίληψη -----------

-- 
Edward Justin Modestino, Ph.D.
Neuroscientist/Faculty
Atlantic University

-- 
---------  αντίληψη -----------

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