avgoverfreq is good or bad?

[Manish Saggar]

Dear Eric,

Thanks for explaining in detail and apologies for late reply, I was on vacation.

Regards,
m-


On Sat, Nov 20, 2010 at 6:41 AM, Eric Maris <e.maris at donders.ru.nl> wrote:
> Dear Manish,
>
>
> As a rule, whenever you incorporate valid prior information in your
> statistical analysis, you will increase sensitivity. For instance, assume
> that there physiological reasons why effects should always occur in a number
> of discrete frequency bands; [0.5,1.5] (delta), [4,6] (theta), [8,12]
> (alpha), [13,30] (beta), and [31,80] (gamma). Then, you will increase power
> by (1) estimating the average power in these frequency bands (using
> multitaper estimation with the appropriate spectral smoothing), and (2)
> performing a cluster-based permutation test on the resulting
> (channel,frequency bin)-data. Without frequency smoothing in the a priori
> defined frequency intervals sensitivity will be lower, assumed the intervals
> are valid of course. You can further increase sensitivity if you know a
> priori that effects will only occur in one of the frequency bands, but that
> does not seem to be the case for you.
>
> Good luck,
>
> Eric Maris
>
>
> dr. Eric Maris
> Donders Institute for Brain, Cognition and Behavior
> Center for Cognition and F.C. Donders Center for Cognitive Neuroimaging
> Radboud University
> P.O. Box 9104
> 6500 HE Nijmegen
> The Netherlands
> T:+31 24 3612651
> Mobile: 06 39584581
> F:+31 24 3616066
> E: e.maris at donders.ru.nl
>
>
>
>
>
>
>
>> -----Original Message-----
>> From: FieldTrip discussion list [mailto:FIELDTRIP at NIC.SURFNET.NL] On
>> Behalf Of Manish Saggar
>> Sent: zaterdag 20 november 2010 8:21
>> To: FIELDTRIP at NIC.SURFNET.NL
>> Subject: [FIELDTRIP] avgoverfreq is good or bad?
>>
>> Dear all,
>>
>> I have spatio-spectral EEG data (no temporal information) from two
>> groups. Group A was tested three times (t1,t2,t3) during a treatment
>> and group B (control group) was also tested at the same three time
>> points. Now I simply want to know which <channel, frequency> pairs
>> differ for each group separately. Thus, I ran depsamplesF test
>> (cluster with montecarlo) for each group for a large frequency range,
>> say 0.5 - 100Hz, cfg.avgoverfreq = 'no'.  I then used Bonferroni
>> correction (for two tests) and plotted the clusters using multiplotTFR
>> with 'mask' as zstat parameter. The clusters of <ch, freq> I get are
>> mostly in 15-40Hz range and usually there is only one big cluster.
>>
>> Now my question is - by running over a huge range of frequency (using
>> no averaging over freq), did I lower the power for low freq bands
>> (like delta, theta, and alpha)? Should I rather run these tests
>> separately for low freq bands (like delta, theta, and alpha) with
>> avgoverfreq='yes'. And may be another test for high frequencies like
>> 14-100 Hz with no averaging over frequencies.
>>
>> The reason I was running one test for all frequencies was to avoid
>> multiple tests and hence avoiding more stringent Bonferroni
>> correction.
>>
>> Thanks,
>> m-
>>
>>
>>
>> Manish Saggar,
>> Doctoral Candidate,
>> Department of Computer Science,
>> The University of Texas at Austin,
>> Web: http://www.cs.utexas.edu/~mishu/
>> Email: mishu at cs.utexas.edu
>>
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>> and to discuss  new ideas for MEG and EEG analysis.
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>
> ---------------------------------------------------------------------------
> You are receiving this message because you are subscribed to
> the  FieldTrip list. 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/neuroimaging/fieldtrip.
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You are receiving this message because you are subscribed to
the  FieldTrip list. 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/neuroimaging/fieldtrip.
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