[Eeglablist] Effects of filter choice on time-frequency type analyses

Ng Eric goodieskk at gmail.com
Mon Apr 21 22:11:59 PDT 2014

Dear all,

I plan to perform some time-frequency analyses on task and resting EEG
data, but I am concerned about the effect causal/non-causal filtering on
analyses involving phase measures.

The default in pop_eegfiltnew (on EEGLAB v11.0.4.3b or v13.2.1) is a
'non-causal' filter (minphase setting = 0, thus applying filtfilt). It
seems that non-causal filters 'distort' the causal relationships between
signals, but unlike causal filters, which introduce a linear phase shift
across frequencies. If I am going to do e.g., phase locking between
different frequencies or phase-amplitude coupling, will the phase shifts
affect the validity of the results (i.e., don't use causal filters)? Or is
there anything more undesirable with the correction of phase lag on phase
measures (i.e., don't use non-causal filters)?

I am still a novice on signal processing, so any comments and corrections
on wrong concepts will be very helpful. Thank you very much!

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