[Eeglablist] <no subject>

[Scott Makeig]

Guilia -

To combine datasets with 128 and 64 channels, construct an EEGLAB STUDY
containing datasets with 64 channels. Does the 128-channel montage include
the 64-channel montage as a subset? If so, the reduction from 128- to
64--channel datasets should be simple.

If not, then you may want to spatially resample. My suggested approach for
that would be to perform ICA (optimally, see the wiki tutorial) on each of
the 128-channel data sets, then resample the 3-D projection of each
independent component to the locations of the the 64 channels used in your
other datasets. There is not an EEGLAB function to do just that, but it
should not be difficult (for someone) to build. Then reconstitute each
128-channel data set by summing the back-projections of all the 128
components (perhaps omitting selected 'noise' components) to the 64
channels. Note that you will then no longer be able to separate all (<=) 128
components when you decompose the new data using ICA (since the data now
have only 64 degrees of freedom).

A possibly simpler those less refinable method would be to sample the 64
channels in the interpolated scalp maps of every raw data point - requiring
the same scalp map resampling function.

Resampling the data from 64 to 128 channels is probably less optimal (and
less efficient). For one, it would still allow recovery of only 64
independent components because the rank of the data matrix (>>help rank)
would remain 64, even when 128 channels have been resampled from the scalp
maps.

Scott Makeig

On Tue, Apr 5, 2011 at 8:23 AM, Giulia Righi <grighi at gmail.com> wrote:

>  HI all
>
> I was wondering whether there is a way to combine datasets with different
> numbers of channels (64 and 128 channel nets) to include all participants
> within a study design to run ERSPs and ITCs?
>
> thank you
>
> giulia
>
>
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-- 
Scott Makeig, Research Scientist and Director, Swartz Center for
Computational Neuroscience, Institute for Neural Computation & Adj. Prof. of
Neurosciences, University of California San Diego, La Jolla CA 92093-0559,
http://sccn.ucsd.edu/~scott
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