neuromag data analysis

Virginie van Wassenhove vvw at CALTECH.EDU
Tue Jan 13 18:01:05 CET 2009

Hello Fieldtrip-ers and happy new year!

I am trying to get some Neuromag (MEG) data analysis done with Fieldtrip - so
far I had used fieldtrip for EEG. I can read the data fine (segmentation via
meg-pd) but there are a couple of issues now.

1. when I try to filter or downsample I am receiving the following errors: 

%FILTER (lpf specified in cfg)
blah = timelockanalysis(cfg,data_std_bc);
the input is timelock data with 306 channels and 801 timebins
applying preprocessing options
??? Undefined function or method 'butter' for input arguments of type 'double'.

Error in ==> preproc_lowpassfilter at 80
    [B, A] = butter(N, max(Flp)/Fn);

Error in ==> preproc at 360
if strcmp(cfg.lpfilter, 'yes'),     dat = preproc_lowpassfilter(dat,
fsample, cfg.lpfreq, cfg.lpfiltord,
cfg.lpfilttype, cfg.lpfiltdir); end

Error in ==> timelockanalysis at 318
  [data.trial{i}, data.label, data.time{i}, cfg.preproc] =
preproc(data.trial{i}, data.label,
  data.fsample, cfg.preproc, data.offset(i));
??? Error: File: isequal.m Line: 1 Column: 1
The input character is not valid in MATLAB statements or expressions.

Error in ==> checkdata at 145
if ~isequal(feedback, 'no')

Error in ==> resampledata at 60
data = checkdata(data, 'datatype', 'raw', 'feedback', 'yes');

The data structure looks fine to me:

data_dev1 = 
        hdr: [1x1 struct]
      label: {306x1 cell}
      trial: {1x101 cell}
       time: {1x101 cell}
    fsample: 1000
       grad: [1x1 struct]
        cfg: [1x1 struct]

data_dev1.grad =
      pnt: [510x3 double]
      ori: [510x3 double]
      tra: [306x510 double]
     unit: 'cm'
    label: {1x306 cell}

Any idea on these error messages?

2. The second issue is that doing a timelockanalysis on these data returns
no neg or pos clusters. There is no error message and the computations seem
to run fine.

Am I missing some steps in the preliminary stages of data analysis for MEG
in fieldtrip?

Thanks for any help you may provide,


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