[FieldTrip] [SPAM?] Re: problem with ft_multiplot and planar gradient 

Luisa Frei l.frei at psy.gla.ac.uk
Fri Feb 4 11:43:59 CET 2011

Thanks Michael and Jan-Mathijs,
this is very useful information. I do all the averaging before  
computing the gradients. However, to resolve this I have to admit  
that I found a bug in my code last night and after fixing it, it  
looked fine.

Thanks for your help!

On 4 Feb 2011, at 09:47, Michael Wibral wrote:

> Dear Luisa,
> I was also wondering whether you were aware of the fact that planar  
> gradients of group data can look very different depending on when  
> you do the averaging and the megplanar/combineplanar steps. This is  
> because combineplanar is a nonlinear step that cannot be exchanged  
> with the other steps without changing the results.
> So creating planar gradients in single trials and then using  
> combineplanar and then averaging trials within subjects and then  
> over subjects will look pretty different from doing all averaging  
> first (trials, subjects) and then using megplanar/combineplanar to  
> get an planar gradient representation of this average.
> Michael
> -----Ursprüngliche Nachricht-----
> Von: "Luisa Frei" <l.frei at psy.gla.ac.uk>
> Gesendet: Feb 3, 2011 7:07:44 PM
> An: "Email discussion list for the FieldTrip project"  
> <fieldtrip at donders.ru.nl>
> Betreff: [FieldTrip] problem with ft_multiplot and planar gradient  ?
>> Hi everybody,
>> I have a problem that impacts several analysis steps and I'm hoping
>> someone can point me to the right direction.
>> I have 13 recording sessions, that I want to average, and then I want
>> to compute the planar gradients of the average. I first average the
>> sessions with ft_timelockanalysis for each session. Then I use
>> ft_timelockgrandaverage to combine the sessions.
>> Then, just to check the data, I plot the ERFs with ft_multiplotER.
>> This is when the first problem arises. The x and y axes of the plots
>> are shifted in space somehow (see picture 3.png).
>> Next, I compute the planar gradients. When I plot the topographies
>> for the planar gradient, I get a very strange activation pattern,
>> that has nothing to do with the ERF topography (which, btw has no
>> obvious flaws) and I also get several warnings when I make the plot
>> (Picture4.png).
>> I also know for a fact that the grand average planar gradient should
>> look different, as I computed it once before by hand, and it looked
>> much more sensible.
>> If anyone has ever seen this before and can give me a hint as to
>> where to look for the error, I would be very grateful.
>> Luisa
>> <Michael Wibral.vcf>
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