[FieldTrip] calculating correlation

Ingrid Nieuwenhuis inieuwenhuis at berkeley.edu
Sun Jul 1 22:15:56 CEST 2012

Hi FTers,

I'd like to do two sorts of correlation calculations, and was wondering 
if there's any easy way to do this within FieldTrip.

1) I'd like to calculate the correlation between performance over trials 
and power within a specific frequency over trials. So I have the 
performance measure per trial, and my chan*freq measure after 
freqanalysis. So for each channel I have a series of power values 
(trials) and I have a series of performance measures (per trial), and 
now like to know (first within, and then over subjects) which channel's 
frequency power follows (correlates) with the performance.

 From the walkthrough 
<http://fieldtrip.fcdonders.nl/walkthrough#correlation> I understand I 
can give in these performance measures through the design 
(cfg.design=[];cfg.ivar=1;), but which method 
to use for ft_freqstatistics? I don't see statistics = 'correlation' or 
'pearson' or 'spearman' in method = 'analytic. Also how to make the 
design to correlate over trials?

2) I'd like to calculate the correlation between the score on repeated 
questionnaire over participants with power within a frequency. So I have 
several power values per participant for each channel, and the repeated 
scores on the questionnaire for each participant. And now I'd like to 
calculate a value per channel reflecting the correlation over the 
repeats of the questionnaire and over participants.

Any idea on FieldTrip settings? Both in general, is there a correlation 
statistics implemented, and more specifically for my question, how would 
I make the appropriate designs?

Thanks so much!

Ingrid Nieuwenhuis PhD
Postdoctoral Fellow
Sleep and Neuroimaging Laboratory
Department of Psychology
University of California, Berkeley
California 94720-1650
Tolman Hall, room 5305

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