[FieldTrip] fieldtrip Digest, Vol 31, Issue 32

[Tineke Grent-'t-Jong]

Hi Karen,

Aaron is right that it could be an effect of de-trending or high-pass 
filtering. You could try running the ft_timelockanalyis step again with 
option cfg.removemean = 'no' ('yes' is the default option!). If this
solves the problem then it indeed was some kind of de-trending problem.

Cheers,
Tineke



----- Original Message ----- 
From: "Aaron Schurger" <aaron.schurger at gmail.com>
To: "Tineke Grent-'t-Jong" <t.grent-tjong at donders.ru.nl>; "FieldTrip 
discussion list" <fieldtrip at science.ru.nl>
Sent: Monday, June 17, 2013 3:08 PM
Subject: Re: [FieldTrip] fieldtrip Digest, Vol 31, Issue 32


> Hi, Karen, Tineke,
> To me it looks like more than just a baseline shift. It looks like
> either linear de-trending or high-pass filtering was applied to the
> BVA data. I don't see how a baseline shift could get rid of the low
> frequency component that is clearly visible in the FT plot, but not
> the BVA plot.
> Cheers,
> Aaron
>
> On Mon, Jun 17, 2013 at 2:55 PM, Tineke Grent-'t-Jong
> <t.grent-tjong at donders.ru.nl> wrote:
>> Hi Karen,
>>
>> To me it looks like the only thing you need to do is subtract the 
>> baseline,
>> like you have done in BVA (specifying the same window with cfg.baseline =
>> [xmin xmax], not 'yes'). The average ERP that you are plotting in BVA has
>> already been baselined, but the single trials that go into the
>> ft_timelockanalysis function are not, hence the need for baselining 
>> later,
>> like in your case at the level of plotting.
>>
>> Hope this helps,
>>
>> Tineke
>>
>>
>> ----- Original Message ----- From: <fieldtrip-request at science.ru.nl>
>> To: <fieldtrip at science.ru.nl>
>> Sent: Monday, June 17, 2013 1:56 PM
>> Subject: fieldtrip Digest, Vol 31, Issue 32
>>
>>
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> -- 
> Aaron Schurger, PhD
> Post-doctoral researcher
> INSERM U992 / NeuroSpin
> CEA - Saclay, France
> +33-1-69-08-66-47
> aaron.schurger at gmail.com
> http://www.unicog.org
>