[FieldTrip] Source localization

Casper van Heck caspervanheck at gmail.com
Fri Jan 18 15:53:11 CET 2013


Dear Fieldtrippers,

I've asked this question earlier, but either it got lost due to technical
reasons, or the people who actually understand what's happening here were
on vacation, so here it is again:

I've been trying to do a source analysis on a dataset with two conditions,
mostly following the tutorials and examples from the Fieldtrip site, and
come upon a problem; it won't plot. While the source analysis is not an
essential component of the analysis of this dataset (it's more along the
lines of "let's see if I can do this"), and I don't expect any result other
than something like "there might be a source in the left hemisphere", I'd
still would like to found out why it's not working.

Essentially, I create a standard headmodel cause I don't have individual
MRI's from the "Subject1.mri"-example, using ft_volumesegment,
ft_prepare_headmodel and ft_prepare_sourcemodel, and try to get Fieldtrip
to find sources based on individual EEG-datasets using ft_freqanalysis
(with cfg.method = 'mtmfft') and ft_sourceanalysis.
After that, I use ft_sourcegrandaverage to produce, well, a grand average
source, and feed this via ft_sourceinterpolate to ft_sourceplot.

Now, ft_sourceplot has three plotting possibilities: slice, ortho, and
surface. Initially I tried to get the ortho-option to work, but this gave
the following error:
*Attempted to access dim(3); index out of bounds because numel(dim)=2.*
*Error in ==> cornerpoints at 11
*
*Error in ==> ft_plot_slice at 157
*

So, I tried the surf-option, which gave me this:
*Undefined function or variable "val".*
*Error in ==> ft_sourceplot at 1174
*

And finally, I tried the slice-option, which gave one of two errors (which
seems to be based on how many slices I requested):
*Out of memory*
Which is pretty damn impressive since I've got 8GB of RAM and a pagefile
topping of at 40GB
Or, the mildly disconcerting:
*Matlab has encountered an internal error and has to close*
Which seems to have been caused by a so-called *"Segmentation violation"
*

Can anyone offer any insight in these errors? I think I'm doing something
wrong pretty early on, but have no idea what it is.

Sincerely,

Casper van Heck


On Fri, Dec 21, 2012 at 1:43 PM, Casper van Heck <caspervanheck at gmail.com>wrote:

> Dear Fieldtrippers,
>
> I've been trying to do a source analysis on a dataset with two conditions,
> mostly following the tutorials and examples from the Fieldtrip site, and
> come upon a problem; it won't plot. While the source analysis is not an
> essential component of the analysis of this dataset (it's more along the
> lines of "let's see if I can do this"), and I don't expect any result other
> than something like "there might be a source in the left hemisphere", I'd
> still would like to found out why it's not working.
>
> Essentially, I create a standard headmodel cause I don't have individual
> MRI's from the "Subject1.mri"-example, using ft_volumesegment,
> ft_prepare_headmodel and ft_prepare_sourcemodel, and try to get Fieldtrip
> to find sources based on individual EEG-datasets using ft_freqanalysis
> (with cfg.method = 'mtmfft') and ft_sourceanalysis.
> After that, I use ft_sourcegrandaverage to produce, well, a grand average
> source, and feed this via ft_sourceinterpolate to ft_sourceplot.
>
> Now, ft_sourceplot has three plotting possibilities: slice, ortho, and
> surface. Initially I tried to get the ortho-option to work, but this gave
> the following error:
> *Attempted to access dim(3); index out of bounds because numel(dim)=2.*
> *Error in ==> cornerpoints at 11
> *
> *Error in ==> ft_plot_slice at 157
> *
>
> So, I tried the surf-option, which gave me this:
> *Undefined function or variable "val".*
> *Error in ==> ft_sourceplot at 1174
> *
>
> And finally, I tried the slice-option, which gave one of two errors (which
> seems to be based on how many slices I requested):
> *Out of memory*
> Which is pretty damn impressive since I've got 8GB of RAM and a pagefile
> topping of at 40GB
> Or, the mildly disconcerting:
> *Matlab has encountered an internal error and has to close*
> Which seems to have been caused by a so-called *"Segmentation violation"
> *
>
> Can anyone offer any insight in these errors? I think I'm doing something
> wrong pretty early on, but have no idea what it is.
>
> Sincerely,
>
> Casper van Heck
>
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