Ft_definetrial and ft_preprocessing require the original MEG dataset, which is available from ftp://ftp.fcdonders.nl/pub/fieldtrip/tutorial/Subject01.zip.
% find the interesting segments of data
cfg = []; % empty configuration
cfg.dataset = 'Subject01.ds'; % name of CTF dataset
cfg.trialdef.eventtype = 'backpanel trigger';
cfg.trialdef.prestim = 1;
cfg.trialdef.poststim = 2;
cfg.trialdef.eventvalue = 9; % event value of FC
cfg = ft_definetrial(cfg);
% remove the trials that have artifacts from the trl
cfg.trl([2, 3, 4, 30, 39, 40, 41, 45, 46, 47, 51, 53, 59, 77, 85],:) = [];
% preprocess the data
cfg.channel = {'MEG', '-MLP31', '-MLO12'}; % read all MEG channels except MLP31 and MLO12
cfg.demean = 'yes'; % do baseline correction with the complete trial
dataFC = ft_preprocessing(cfg);
These data have been cleaned from artifacts by removing several trials and two sensors; see the visual artifact rejection tutorial.
Subsequently you can save the data to disk.
save dataFC dataFC
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