[Eeglablist] dB / mV inconsistencies

[Makoto Miyakoshi]

Dear Chrissy,

If I were you I would z-score the data too.

z-scoring by definition subtract means so you don't need to do it manually.
Matlab command zscore does (X-mean(X))./std(X) so what you need to do is
EEG.data = single(zscore(double(EEG.data), 0, 2));
is the data are continuous (see also 'help zscore').
After zscoring the data you may want to make the variance matched by
rescaling to the other dataset.

Before zscoring, you may also want to clean the data (i.e. discarding huge
artifacts) so that std estimation works better.

Makoto


2013/7/1 Chrissy Lackner <cl02zz at brocku.ca>

> EEGlab list,
> I have inherited a set of longitudinal EEG data from a colleague, and
> it seems as though there was an error made while recording the data
> during one of the two time points for one participant. The dB and uV
> are WAY off for time one. They are not even comparable to the uV for
> time two, or comparable to any other subject at time 1. It does look
> like there is meaningful data underlying all of this, and I am hoping
> someone can help me figure out a way to extract all of this data so I
> don't have to loose this participant.
>
> I've uploaded here  (http://db.tt/fqCZK0xM OR here
> http://db.tt/sXxiYREU)  a screenshot of their time one data (note the
> scale on the bottom right and the odd TF decomposition) as well as
> their time two data (normal).
>
> I have tried re-referencing to average, refiltering, removing the
> 'real' channel mean as discussed in a previous list message:
>
> > % remove *real* channel mean
> >      for numChans = 1:size(EEG.data,1);
> >      EEG.data(numChans, :) = single(double(EEG.data(numChans, :)) -
> > mean(double(EEG.data(numChans, :))));
> >     end
>
> And finally I've tried normalizing (zscoring the data). This last
> approach seems promising, although it means that I'd have to
> re-process all other participants in this manner. Perhaps there is a
> way to scale down the uV in a way that I haven't come across?
>
>   Any ideas?
>   Thanks for your help.
>   Chrissy
>
>
>
>   Chrissy Lackner, MSc
>   PhD Candidate, Behavioural Neuroscience
>   Brock University | Psychology Department
>   Niagara Region   |  500 Glenridge Ave.  |  St. Catharines, ON  L2S 3A1
>   brocku.ca | T  905 688 5550 x5511
>
>
>
>
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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