Significance test frequency power decrease baseline vs stimulation

[Thomas Dijkman]

Hi,

I'm currently in the pilot phase, testing various stimuli on myself and my supervisor. I want to do this analysis to get an indication which stimulus has the best potential, so I can test that on a sufficient large group.

The data I'm testing the statistical analysis script on consists of 50 trials, the subject was asked to perform motor imagery while looking at the screen. Each trial consists of 3 seconds baseline (empty background on screen) and 5 seconds stimulus ( hand squeezing a ball on screen).
I don't need the TFR's of the individual trials, since the mean TFR will (that's what I expect) show a more prominent in power in the 8-13 Hz band when I compare baseline vs stimulus.

The error message I get when I run the script now is:

??? Undefined variable "data" or class "data.biol".

Error in ==> prepare_design at 92
  nrepl=size(data.biol,1);

Error in ==> statistics_wrapper at 238
  [cfg] = prepare_design(cfg);

Error in ==> freqstatistics at 132
[stat] = statistics_wrapper(cfg, varargin{:});

Error in ==> fieldtripstatanalyse at 36
[stat] = freqstatistics(cfg, stimulusTFR, baselineTFR);

Thanks for your input,

Thomas


-----Oorspronkelijk bericht-----
Van: FieldTrip discussion list namens Nathan Weisz
Verzonden: do 26-6-2008 8:45
Aan: FIELDTRIP at NIC.SURFNET.NL
Onderwerp: Re: [FIELDTRIP] Significance test frequency power decrease baseline vs stimulation
 
hi,

you want individual subject stats? i'm pretty sure then that you need  
to add something like
cfg.keeptrials='yes';
when doing your freqanalysis.

btw, adding the actual error message is also a good idea when posting  
questions.

good luck,
n


On 26.06.2008, at 00:09, Thomas Dijkman wrote:

> Hi,
>
> For my bachelor's assignment, I'm trying to find a visual stimulus  
> of a hand
> movement that triggers the 'largest' modulation of the EEG. I.e. ,  
> when the
> subject looks at a right hand movement, literature suggest a  
> decrease in
> power in the 8-13 Hz band, relative to a baseline period around  
> electrode
> position C3.
> I'm trying to use Fieldtrip's freqstatistics.m function to test this
> decrease in power for significance. Following a tutorial in the  
> Fieldtrip wiki,
> http://www2.ru.nl/fcdonders/fieldtrip/doku.php?id=fieldtrip:documentation:tutorial:statistics&s=freqstatistics#3.2_permutation_tests_for_time-frequency_representationswithin_trial_experiments
>
> which I thought applied to my situation gave me a lot of error  
> messages.
>
> I've already redefined my trials, so I have a separate set of  
> trials, one
> containing 2 seconds of baseline, and one containing 2 seconds of  
> stimulus.
> The baseline time axis is shifted so it overlaps the stimulus time  
> axis
>
> I then use this code to calculate TFR's for those datasets:
>
> cfgfreq.method = 'mtmconvol';
> cfgfreq.output = 'pow' ;
> cfgfreq.taper = ' hanning' ;
> cfgfreq.foi = 8:1:13;
> cfgfreq.t_ftimwin = 10./cfgfreq.foi;
> cfgfreq.toi = 5:1/100:7;
> cfgfreq.tapsmofrq = cfgfreq.foi*0.4;
> [baselineTFR] = freqanalysis(cfgfreq,baselinedata);
> [stimulusTFR] = freqanalysis(cfgfreq,stimulusdata);
>
> And then I have to do the significance test.
>
> cfg = [];
> sfg.method = 'analytic';
> cfg.statistics = 'actvsblT';
> cfg.alpha = 0.05;
> ?
> [stat] = freqstatistics(cfg,stimulusTFR,baselineTFR);
>
> I think I have to do something with the design matrix, but I can't  
> find
> anything about that in the wiki (or the rest of the internet).
>
> Thanks,
>
> Thomas
>
> ----------------------------------
> The aim of this list is to facilitate the discussion between users  
> of the FieldTrip  toolbox, to share experiences and to discuss new  
> ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html 
>  and http://www.ru.nl/fcdonders/fieldtrip.

--------------------------------
Dr. Nathan Weisz

INSERM - Unité 821
Dynamique cérébrale et cognition
Centre Hospitalier Le Vinatier, Bâtiment 452
95 Boulevard Pinel
69500 Bron, France

Tel: ++33 - (0)4 - 7213 8915
Email: nathan.weisz at inserm.fr
Chat-AV: nathanweisz at mac.com
Homepage: http://web.mac.com/nathanweisz
Neurotree: http://neurotree.org/neurotree/tree.php?pid=8692

Please avoid sending me Word or PowerPoint attachments.
See http://www.gnu.org/philosophy/no-word-attachments.html





----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.

----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.