[FieldTrip] ERPs "the other way round"

[Oostenveld, R. (Robert)]

Dear Bence,

Where do you get the electrode positions from that you find in your data.elec.chanpos? I don’t believe those are read from the BDF file, and we don’t include a templatein FieldTrip for the 3D locations corresponding to the Biosemi electrode caps. If you go to https://urldefense.com/v3/__https://www.biosemi.com/headcap.htm__;!!HJOPV4FYYWzcc1jazlU!5mHOs_kqWRej8db0vZpBoOxGy13wpWoE12YLTElAhZeE0mRka2mVvdEQ-8ffAdDAg72kZJ0rolT-XQeouNnMF3nnk3jz7rIQ4oADog$  you can see how the channel names map on to the position of the electrodes over the left and right hemisphere and there you can also find an excel file with positions, which includes a definition of x, y and z.

best
Robert





On 13 Jul 2023, at 00:40, Bence Szaszkó via fieldtrip <fieldtrip at science.ru.nl> wrote:

Dear Group Members,

I am struggling a bit with an ERP analysis in Fieldtrip - calculating distractor positivity (Pd), I subtracted ipsilateral from contralateral effects. I get an effect, but exactly the opposite as expected. I looked at my code multiple times and did not find any mistakes.

However, when looking at channel positions in data.elec.chanpos, it appears that the coordinates for Biosemi 128 are „flipped“ between X and Y, so instead of XYZ it is YXZ. Is this common or could this be the reason for my results?

Kind regards,
Bence

--
Bence Szaszkó, BSc MA MSc
University Assistant (prae doc)

Vienna Doctoral School CoBeNe
PhD Representative

University of Vienna
Faculty of Psychology
Department of Cognition, Emotion, and Methods in Psychology

Liebiggasse 5
A-1010 Wien/Vienna
Austria

e-mail: bence.szaszko at univie.ac.at

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