filtering after preprocessing

Robert Oostenveld r.oostenveld at FCDONDERS.RU.NL
Mon Aug 28 21:54:42 CEST 2006


Dear Lilla

On 23 Aug 2006, at 13:38, Lilla Magyari wrote:
> ...results look to be noisy when I plot them. Therefore, I would
> like to ask if
> it is possible to filter my data after preprocessing in Fieldtrip
> (I haven't
> found any function for filtering separately from the preprocessing
> function)? Or does filtering work only during preprocessing?

You can use timelockanalysis for that. That function has hidden
options (i.e. they are not documented if you type "help
timelockanalysis", but you can read about them if you open the
timelockanalysis funciton in the matlab editor) with exactly the same
syntax as preprocessing. With those cfg options you can specify
filtering, rereferencing etc. on your already averaged data. Of
course you cannot do any filter padding, since that requires the data
to be used for the padding to be re-read from file (which is possible
during preprocessing, but not during timelockanalysis).

So the idea is

cfg = ...
raw = preprocessing(cfg);

cfg = [];
avg = timelockanalysis(cfg, raw);

cfg = [];
cfg.lpfilter = 'yes';
cfg.lpfreq = 30;
avg_f = timelockanalysis(cfg, avg);

best regards,
Robert



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