[FieldTrip] computing threshold for PLV

[jan-mathijs schoffelen]

Dear all,

Note that shuffling the epochs with respect to one another (where for one of the channels in the pair the epoch order stays fixed) usually yields a too liberal null-distribution. The reason is that the shuffling also destroys all structure in the data that is due to electromagnetic field spread. So, even if an observed pattern of PLV is caused by a single underlying neural generator, shuffling the epochs most likely makes this pattern 'significant'. However, it still does not reflect physiological interaction between sources.

Best,
Jan-Mathijs


On May 18, 2013, at 6:37 PM, Sheraz Khan wrote:

> You can randomly shift in time the epochs, to compute null-distribution, and then threshold at some  p-value say p < 0.01, you can even correct for multiple comparison in space and time using  this principle.
> 
> 
> 
> On Sat, May 18, 2013 at 12:21 PM, Subramaniam Iyer <eeguser at hotmail.com> wrote:
> Dear FT Experts,
> 
> I have calculated PLV for a set of EEG data from 5 different patients. Now I want to convert the PLV matrix of each patient into a binary matrix. For this I need a threshold PLV value below which I can assume the phase locking is zero.
> My question is, how do I compute this threshold. I know hard thresholding is one option ( for ex setting 0.1 or 0.2 as threshold), but I guess it is not a very good option.
> 
> Can somebody suggest a better and robust (statistical) way of determining the threshold ? 
> 
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Jan-Mathijs Schoffelen, MD PhD 

Donders Institute for Brain, Cognition and Behaviour, 
Centre for Cognitive Neuroimaging,
Radboud University Nijmegen, The Netherlands

Max Planck Institute for Psycholinguistics,
Nijmegen, The Netherlands

J.Schoffelen at donders.ru.nl
Telephone: +31-24-3614793

http://www.hettaligebrein.nl

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