generating data structure for all trials

[Robert Oostenveld]

Hi Sameer,

To add a few statements to Christians reply

On 8 Feb 2007, at 18:59, Sameer Walawalkar wrote:
> However, while using Fieldtrip, the first point where a MATLAB
> variable
> containing data is created is during trial definition at
> data = preprocessing(cfg); (from online tutorial)
> Trial rejections, and independent component analysis is done after
> this.
>
> Instead I would prefer to  use independent  component analysis
> first  to
> remove blinks etc, then do channels and trial rejections, and then
> do the
> trial definitions based on event types etc.

If you do everything in FT, then you would do it like this
   definetrial -> preprocessing -> componentanalysis ->
rejectcomponent -> freqananlysis -> sourceanalysis -> sourcestatistics
and the datastructures would look like
    only cfg   -> raw data (1)  -> raw data (2)      -> raw data
(3)    -> freq          -> source          -> source

So the same datastructures are used multiple times, only the content
slightly changes. Even if you decide not to do everything within FT,
it is relevant to know that there are not that many data structures
in FT and that raw data can be used in multiple fashions. Regarding
the raw data above
- the 1st raw data is the original. It is cut into segments, and
could in principle be a single segment but that is probably not
desirable for the freqanalysis later (and certainly not for
statistics in the end).
- the 2nd raw data consists of the component timecourses, and
includes the ICA mixing matrix
- the 3rd raw data is again mixed and contains channel data, but now
without the artifacts
Using the same raw data representation allows us to do freqanalysis
or timelockanalysis on both channel-level "raw" data and on ICA-level
"raw" data.

I don't think that rejectcomponent is in the ftp version, please find
it attached. I will also put it on the ftp server.

Also have a look at http://www2.ru.nl/fcdonders/fieldtrip/doku.php?
id=fieldtrip:documentation:use_independent_component_analysis_ica_to_rem
ove_ecg_artifacts

best regards,
Robert
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