[Eeglablist] What is the unit of datas in EEG.data

[Andreas Widmann]

Hi,

> Thank you for your response. My data format come from Brain Vision so I don't use loadvg(). I use pop_loadbv and this function save units because it is written :
> for chan = 1:length(chans)
>         [EEG.chanlocs(chan).labels, chanlocs(chan).ref, chanlocs(chan).scale, chanlocs(chan).unit] = strread(hdr.channelinfos{chans(chan)}, '%s%s%s%s', 1, 'delimiter', ',‘);
This is written into a temporary chanlocs structure here, but not yet written into EEG.chanlocs. There is some fragmentary commented code some lines below (which should have never worked). Not sure why it is fragmentary and where it came from. Most likely there were compatibility issues with Octave and/or character sets between different OS.

On MATLAB under Linux it is sufficient to add a single line 130:
EEG.chanlocs(chan).unit = char(chanlocs(chan).unit);

Then you get units into your EEG.chanlocs structure. Might or might now work with Octave and/or Win/OS X.

Best,
Andreas

> However, it doesn't appear in the workspace of Matlab... chanlocs.unit is undefined. 
> 
> Best,
> 
> Fanny
> 
> 
> 2014-04-25 6:05 GMT+02:00 Stephen Politzer-Ahles <spa268 at nyu.edu>:
> I think there is one exception, which is that the loadavg() function for Neuroscan .avg data does some kind of scaling (see see http://sccn.ucsd.edu/pipermail/eeglablist/2011/003986.html and some other messages on the list) so the data aren't in microvolts or (I think) a straightforward multiple of microvolts. I'm not sure if that's your data format, but if it is then that message includes a different function you can use to get the data in microvolts.
> 
> Best,
> Steve
> 
> 
> 
> Stephen Politzer-Ahles
> New York University, Abu Dhabi
> Neuroscience of Language Lab
> http://www.nyu.edu/projects/politzer-ahles/
> 
> 
> On Fri, Apr 25, 2014 at 7:19 AM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu> wrote:
> Dear Fanny,
> 
> That's an interesting question. I guess the unit is fixed to be microvolt, and it's not written anywhere!
> 
> Makoto
> 
> 
> 2014-04-24 0:57 GMT-07:00 GROSSELIN, Fanny <fanny.grosselin at edu.esiee.fr>:
> Hi Makoto,
> 
> Thank you for your response. However, I wonder if unit is saved somewhere in the workspace of Matlab or if I have to get back it in the header file?
> 
> Fanny
> 
> 
> 2014-04-23 22:40 GMT+02:00 Makoto Miyakoshi <mmiyakoshi at ucsd.edu>:
> 
> Dear Fanny,
> 
> I know some of import function can specify the units for amplitudes. If you have problem, you can try
> EEG.data = EEG.data*/1000;
> to convert microvolt to millivolt.
> 
> Makoto
> 
> 
> 2014-04-23 8:13 GMT-07:00 GROSSELIN, Fanny <fanny.grosselin at edu.esiee.fr>:
> Hi everybody,
> 
> I would like to know what the unit of data is in EEG.data? 
> Is there microvolts unit for any type of file loaded, even if data are in millivolts in the initial file?
> 
> Thank you in advance for your help,
> 
> Fanny
> 
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> 
> -- 
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
> 
> 
> 
> 
> -- 
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
> 
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