[Eeglablist] causal filtering pop_eegfiltnew

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Thu Apr 25 09:33:05 PDT 2013


Dear Daniele,

Thank you for your comment.

> if you don't want the phase shift, you should *NOT* check the "use causal
filter" box.

You are right here. But Marta said

> if i want to get a causal filter i should be using the 'legacy' version
of the pop_eegfilt that uses fir1 and firfirl to filter the data?

So she *wants* to use the causal filter for some reason.

Marta, here is additional caution: 'use causal filter' does NOT keep ERP
peak latencies unchanged (if that's what you want to test; here I'm just
guessing).

Makoto



2013/4/25 Daniele Marinazzo <daniele.marinazzo at gmail.com>

> actually from what I see in eegfilt.m, if causal option is *on*, it uses
> filter.m (phase shift introduced), otherwise is causal option is *off* it
> uses filtfilt.m (no phase shift).
>
> so, if you don't want the phase shift, you should *NOT* check the "use
> causal filter" box.
>
> do you confirm this, or is there a confusion with the nomenclature?
>
> d.
>
>
> On Wed, Apr 24, 2013 at 10:10 PM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>wrote:
>
>> Dear Marta,
>>
>> > if i want to get a causal filter i should be using the 'legacy' version
>> of the pop_eegfilt that uses fir1 and firfirl to filter the data?
>>
>> Right. Check the box 'use causal filter' when you run it.
>>
>> Makoto
>>
>>
>> 2013/4/24 Marta Castellano <m at martacastellano.eu>
>>
>>> Dear eeglablist,
>>>
>>> I would need some help regarding the filtering of EEG data.
>>>
>>> I'm currently using the EEGlab 12.0.2.0b and filtering the data with
>>> pop_eegfiltnew, which creates a type 1 windowed synch filter and the
>>> filtering is implemented through firfirlt. As far as I understood, this
>>> leads to a phase shift because of the firfilt, and also, given that the
>>> impulse response of the filter is symetric, the filter is acausal (so that
>>> no causal analysis can be performed).
>>>
>>> Does that means that, if i want to get a causal filter i should be using
>>> the 'legacy' version of the pop_eegfilt that uses fir1 and firfirl to
>>> filter the data?
>>>
>>> Thanks a lot in advance for your help,
>>>
>>> Marta
>>>
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>>
>>
>>
>> --
>> 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
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