[Eeglablist] Unequal group size and STUDY use

[Hilla Jakoby]

Dear all,
 
I've tried to use the new std_erpplot.m function with an unequal number of subjects of each group (25 versus 29) and the same error message was generated when trying to plot their ERPs as before (using the old function). I've interpolated all datasets beforehand to 65 electrodes (using eeg_interp(EEG, chanlocs,'invdist'). was I right in doing so? 
On equal group sizes STUDY works well.
Is there another solution for the problem, other changes to be done?
Many thanks, Hilla
 
 
Ph.D. student
Gonda brain reseach center, 
Bar Ilan Universiy, Israel
 
 


--- On Sun, 11/30/08, arno delorme <arno at ucsd.edu> wrote:

From: arno delorme <arno at ucsd.edu>
Subject: Re: [Eeglablist] Unequal group size and STUDY use
To: "Hamish INNES-BROWN" <HINNES-BROWN at bionicear.org>
Cc: eeglablist at sccn.ucsd.edu, "Michael Stevens" <msteven at harthosp.org>
Date: Sunday, November 30, 2008, 9:40 PM

Dear Michael and Hamish,

thanks for reporting the problem. This issue arises due to the complexity of
the scheme implemented to handle scalp map plotting in the case of subject with
different number of channels. This scheme was currently enforcing to have groups
of the same size. To fix this problem, I have decided to enforce interpolation
so that all subject will need to have the same number of channels (or at least
subset of channels when plotting scalp maps). Scalp maps where the different
channels average different numbers of subjects do not make much sense anyway.
There has also been at least two people reporting plotting problems after
interpolating data, although I have not yet myself been able to reproduce the
problem. I hope the current fix will solve this problem too.

I have reprogrammed the attached std_erpplot.m function so that it can handle
groups of different sizes (although be sure to interpolate missing channels).
Please let me know if this fixes your problems (just replace this function in
the eeglabxxx/functions/studyfunc/ folder) and it will be integrated in the
EEGLAB monthly release. This message was forwarded to the list because it is of
global interest and also because it depicts a problem that is a major current
limitation for most users. In general though, please use the Bugzilla database
for reporting problems.

Best,

Arno

ps: For interpolation, there is currently a non-documented bug: if you
interpolate channels when pre-computing ERPs and then go back to the pre-compute
GUI to compute ERSP without interpolation, the function will crash. This is
because all measure have to be consistent in terms of interpolation. As
described above, the future function will enforce interpolation (which is
relatively fast). In case the function crashed for you, erase all measure data
files (*.daterp, *.datersp, *.datspec, *.datitc), and type on the command line
STUDY.changrp = []; then call back the pre-computing interface.

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