[FieldTrip] Statistics on freq data

[Алексей Бенин]

Hi all!

Does anyone have ideas? :)


>
>
>Dear Fieldtripers,
>
>First of all big thanks for a wonderful tool and support!
>
>I have some questions about cluster based permutation test on TF data.
>I perform a between-trials experiment and want to search differences say 
>on frequencies 10-30Hz and latencies 200-1200 ms from onset.
>So I need to explore these ranges for possible differencies in powerspectrum.
>When I use for example
>
>cfg.latency          = [0.2 1.2];
>cfg.frequency        = [10 30];
>
>I find no significant clusters, and lowest p_value is very high, say 0,8.
>But when I try to look at smaller time/frequency areas, like
>
>cfg.latency          = [0.2 0.3];
>cfg.frequency        = [15 16];
>
>There can be one or two significant clusters with p_values<0.01.
>So my question is: does the algorithm look for the whole specified TF window like
>0.2-1.2s   10-30Hz and tries to find significant difference based on the whole length
>of interval? This could explain why there are no significant clusters on bigger windows.
>Such clusters appear when we shorten the toi and foi - it's much more probable to find differences
>at smaller scales. 
>So the next question is: what should I do to explore the whole number of frequencies and latencies?
>Shall I run a loop with parameters like this:
>
>Iteration 1
>cfg.latency          = [0.2 0.3];
>cfg.frequency        = [15 16];
>
>Iteration 2
>cfg.latency          = [0.3 0.4];
>cfg.frequency        = [15 16];
>
>... and so on?
>
>Or maybe I do not understand something in basis of method? 
>BTW, I've read all tutorials and appropriate papers like
>Nonparametric statistical testing of EEG, but could not find the answer.
>
>
>Thanks in advance,
>
>Alex
>
>
>
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