[Eeglablist] Effect of anti-aliasing low-pass filter on connectivity analysis

[K Jeffrey Eriksen]

I agree that zero phase lag is best. Anything else distorts the phase relationships. I know BESA proponents have argued about “future leaking into the past”, but I think that is simply a common sense notion that is not really true globally.

I wish I could prove it mathematically, but a simple simulation should demonstrate it. Maybe I will get around to it someday.

-Jeff Eriksen

From: eeglablist-bounces at sccn.ucsd.edu [mailto:eeglablist-bounces at sccn.ucsd.edu] On Behalf Of Makoto Miyakoshi
Sent: Tuesday, June 23, 2015 5:59 PM
To: Iman Mohammad-Rezazadeh
Cc: EEGLAB List
Subject: Re: [Eeglablist] Effect of anti-aliasing low-pass filter on connectivity analysis

Dear Iman,

> Using causal filter may adversely effect the direction of information
flow in the GC analysis. It is recommended that one use a
non-causal filter (for example, finite impulse response filters) with
zero phase lag

Really? The impulse response of the non-causal FIR filter spreads in both ways in the time domain, which means info of future events leak to past... I thought using causal filter with minimum phase makes more sense.

Makoto

On Tue, Jun 23, 2015 at 4:29 PM, Iman Mohammad-Rezazadeh <irezazadeh at ucdavis.edu<mailto:irezazadeh at ucdavis.edu>> wrote:
http://journal.frontiersin.org/article/10.3389/fnhum.2015.00194/abstract

Using causal filter may adversely effect the direction of information
flow in the GC analysis. It is recommended that one use a
non-causal filter (for example, finite impulse response filters) with
zero phase lag (Mullen et al., 2012, Coben and Rezazadeh, 2015)


From: eeglablist-bounces at sccn.ucsd.edu<mailto:eeglablist-bounces at sccn.ucsd.edu> [mailto:eeglablist-bounces at sccn.ucsd.edu<mailto:eeglablist-bounces at sccn.ucsd.edu>] On Behalf Of Makoto Miyakoshi
Sent: Tuesday, June 23, 2015 2:07 PM
To: Vito De Feo
Cc: EEGLAB List
Subject: Re: [Eeglablist] Effect of anti-aliasing low-pass filter on connectivity analysis

Thank you Vito for your response. Forgive me to ask you one more question.

As the ERP handbook by Luck (or his other book) recommends, anti-aliasing should better have the margin of 4-5 times of the new sampling rate e.g. if you downsample signlas to 250 Hz, anti-aliasing low-pass at 125 Hz is the standard, but recommendation is 75 Hz or even 50 Hz. Well, I haven't tested it myself so I am not sure what bad it would do if I use 125 Hz (any comment on this, anyone?) but in this case, I guess the anti-aliasing low-pass filter does affect the subsequest connectivity analysis--am I correct (assuming that I analyze EEG up to 50 Hz)?

Makoto

On Mon, Jun 22, 2015 at 9:31 AM, Vito De Feo <vito.defeo at zmnh.uni-hamburg.de<mailto:vito.defeo at zmnh.uni-hamburg.de>> wrote:
Dear Makoto,
this will not affect the connectivity analysis if the frequency of interest are far from the Nyquist frequency. For example if you downsample to 500 Hz (Nyquist freq = 250 Hz) you will have no problem in the band 0-100 Hz.
Best
Vito

Il giorno 20/giu/2015, alle ore 00:28, Makoto Miyakoshi ha scritto:

> Dear List,
>
> If I use zero-phase low-pass filter for anti-aliasing, does it affect the subsequent connectivity analysis? I ask this because EEGLAB pop_resample() automatically applies it. If it does, is there a workaround? Should I use minimum phase causal filter for anti-aliasing?
>
> --
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
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Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego



--
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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