[FieldTrip] using tPCA on EEG data

[philip Joadavi]

Dear Jan-Mathijs,

Thank you so much for your quick reply. I tried it and it's working. I used
'SVD' instead of 'PCA'.
Just to be sure I have a follow-up question, I want to use
*ft_rejectcomponent* after that (I mean after ft_componentanalysis), can I
just use it as it is or I have to do some other tricks also before using
ft_rejectcomponent?

Thanks a lot,
Philip



On Wed, Aug 26, 2020 at 8:42 AM Schoffelen, J.M. (Jan Mathijs) <
jan.schoffelen at donders.ru.nl> wrote:

> Hi Philip,
>
> You could try and hack your way around, by transposing the time courses.
> Assuming you have just a single epoch in your data structure (or all epochs
> have the exact same length)  (otherwise it will not work), you can do: for
> k = 1:numel(data.trial) data.trial{k} = data.trial{k}’ ; end
>
> Then you need to fool Fieldtrip into ’thinking’ that the -what used to be
> the channel dimension- is the time dimension: data.time{:} =
> (1:size(data.trial{1},2))./data.fsample;
>
> and likewise for the new channel dimension:
> for k = 1:size(data.trial{1},1)
> data.label{k} = sprintf(‘chan%05d’,k);
> end
>
> Then Bob’s your uncle, that is, probably ft_componentanalysis will swallow
> the data.
>
> Note however, that the pca algorithm implemented in FT is not very clever,
> so it will probably not deal well with ill-conditioned covariance matrices,
> which you’re likely to end up with, since the number of time points is
> typically much larger than the number of channels.
>
> Best wishes,
> Jan-Mathijs
>
>
> On 25 Aug 2020, at 18:56, philip Joadavi <p.joadavi at gmail.com> wrote:
>
> Dear all,
>
> I would like to work with PCA on my EEG data using Fieldtrip. As far as I
> know, the implementation of PCA in Fieldtrip is only on spatial (i.e the
> variables are the EEG channels ( *spatial PCA*)).
>
> Is that possible to work around the function 'ft_componentanalysis'  to
> perform the *temporal PCA* using field trip?
>
> Thanks!
> Philip Joadavi
>
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