[Eeglablist] ICA on multi-epoch data

[peng]

Dear arno,

   Thank you for your reply. Do you mean that it would get the same
(similar) result if I link all the 120 epochs together (make it look
like one epoch), then perform ICA, then divide the results into 120
epochs at the right time point? I mean within Infomax or FastICA
algorithm.
   Another issue is about the ica algorithm. I'm now using 128-channel
EEG system, which would produce 128 components by default settings of
Infomax algorithm. That would make the computing very slow... And,
biologically, there may be less brain sources (eg. we anticipated to
get less clusters). So I wish to set less components (say, 10-20) for
"runica". However, I am not sure whether it would reduce the accuracy
of ica results.
   And more on ica: If there were 10 "sources", and we pre-set 11
components for our ica program. Then what would the one more component
stand for? Did it mean one source would be interpreted as two
components; or there're possiblities that all 10 "sources" could be
mixed together?
   Thanks again.

Peng

On 2/13/07, arno <arno at salk.edu> wrote:
> Dear Peng,
>
> > I'm using EEGLab to perform ica decomposition. I have an EEG data
> > of 120 epochs (trials).
> > When doing ica, would the data from the same channel (in different
> > epoch) be considered together? If so, how were they combined
>
> Yes, they will be considered together. They are not combined (except if
> you use the SOBI
> ICA algorithm). If you use the standard runica() Infomax algorithm, each
> time point is
> considered independently. You can shuffle them within and across epoch
> and this would
> not change the ICA results (except from minor changes due to starting
> conditions and
> random shuffling of time points at each iteration of the algorithm).
>
> Best,
>
> Arno
>
>