[FieldTrip] ERP average Brain Vision is different from ERP average FieldTrip

[Aaron Schurger]

Hi, Karen,
Yes, you're right - it would have to be the case that the averaging
step in BVA applies the filters. That would be where I would check. If
nothing there then it really is mysterious!
Aaron

On Mon, Jun 17, 2013 at 3:22 PM, Karen Schuil <schuil at fsw.eur.nl> wrote:
> Dear Jim, Aaron, Roemer and Tineke,
>
> Thanks for your quick response and suggestions! The whole preprocessing
> (including the filters) was done in BVA. After segmentatation of the
> conditions, we exported the data to Fieldtrip. The only steps we did in
> Fieldtrip was averaging, creating and plotting an ERP. Therefore it can't be
> the filters, right? Unless, the averaging step in BVA applies filters as
> well.
>
> The ref in AF7-ref is added by BVA and refers to the channels being linked
> to the mastoids.
>
> We have also tried it with subtracting a baseline, but this unfortunately
> did not help.
>
> Do you have any other suggestions?
>
> Cheers, Karen
>
>
>
>
> On Mon, Jun 17, 2013 at 2:25 PM, Aaron Schurger <aaron.schurger at gmail.com>
> wrote:
>>
>> To me it really looks like BVA is applying a high-pass filter at some
>> stage. When you export the data, the high-pass filter has probably
>> already been applied. It is typical in EEG (though not a good idea in
>> my opinion) to apply a high-pass filter with a cutoff at around 0.05
>> or 0.1 Hz. There should be a setting somewhere in BVA to turn off the
>> high-pass filter. Anyway, that's my guess just from looking at the
>> figure you attached.
>> Cheers,
>> Aaron
>>
>> On Mon, Jun 17, 2013 at 1:56 PM, Karen Schuil <karenschuil at gmail.com>
>> wrote:
>> > Dear Fieldtrip Users,
>> >
>> > I have a BVA-Fieldtrip problem. The average ERPs of Brain Vision
>> > Analyser
>> > are different from the ERPS of FieldTrip. It seems that in Fieldtrip a
>> > slow
>> > negative drift is added and peaks are more/less pronounced than in BVA
>> > (attached is a picture of the two different plots).
>> >
>> > An expert FieldTrip User and I could not find a solution for this
>> > problem. I
>> > hope one of you has a suggestion for this problem.
>> >
>> > The individual trial data was exported from BVA (version 2.02.5859) with
>> > the
>> > following settings:
>> > File extension: .seg
>> > Write header file: yes
>> > Write marker file: yes
>> > Format: BINARY
>> > Orientation: MULTIPLEXED
>> > Line Delimiter: CRLF (PC style)
>> > Binary format: 16-Bit signed integer format
>> > Set resolution manually: no
>> > Individually optimized resolution for each channel: yes
>> > Convert to big-endian order: no
>> > Export all channels: no
>> > Export the following channels:
>> > AF3 AF4 AF7 AF8 AFz C1 C2 C3 C4 C5 C6 CP1 CP2 CP3 CP4 CP5
>> > CP6 CPz Cz F1 F2 F3 F4 F5 F6 F7 F8 FC1 FC2 FC3 FC4 FC5
>> > FC6 FCz Fpz FT7 FT8 Fz Iz O1 O2 Oz P1 P10 P2 P3 P4 P5
>> > P6 P7 P8 P9 PO3 PO4 PO7 PO8 POz Pz T7 T8 TP7 TP8
>> > Created Using Component Version 2.0.2.5827
>> >
>> > We used Matlab version 7.10.0 R2, and fieldtrip version 13-06-2013 (and
>> > tried a version from 2011).
>> >
>> > The scripts we used are read_analyzer_data and timelockanalysis. This is
>> > the
>> > code we used for calling the scripts:
>> > % read data into fieldtrip
>> > cfg = [];
>> >
>> > cfg.inputfile = 'pp10_A';
>> > cfg.triggercode = 'S 20';
>> > cfg.triggertype = 'Stimulus';
>> > cfg.prestim = 1.2;
>> > cfg.poststim = 1.7;
>> >
>> > pp10_l = read_analyzer_data(cfg);
>> >
>> > % check: compute ERP
>> > %
>> > cfg = [];
>> > pp10_ERP = timelockanalysis(cfg, pp10_l);
>> >
>> > %plot ERP
>> >
>> > cfg = [];
>> > cfg.layout = 'elec1010.lay';
>> > cfg.xlim = [-0.15 1.7];
>> > cfg.ylim = [-12.25 12.25];
>> > % cfg.baseline = 'yes';
>> > % cfg.baselinetype = 'absolute';
>> > cfg.showlabels = 'yes';
>> > cfg.interactive = 'yes';
>> >
>> > multiplotER(cfg, pp10_ERP);
>> >
>> >
>> > I hope you can help!
>> >
>> > Kind regards,
>> > Karen
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> > _______________________________________________
>> > fieldtrip mailing list
>> > fieldtrip at donders.ru.nl
>> > http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>>
>>
>>
>> --
>> 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
>> _______________________________________________
>> fieldtrip mailing list
>> fieldtrip at donders.ru.nl
>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>
>
>
>
> --
> -------------------
> Karen Schuil
> PhD student
>
> Erasmus University Rotterdam
> Institute of Psychology, T 13-09
> Burgemeester Oudlaan 50
> P.O. Box 1738
> 3000 DR Rotterdam
> The Netherlands
> Phone: +31 (0) 10 408 2293
> Email:  schuil at fsw.eur.nl
>
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip



-- 
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