[FieldTrip] Global field power

[Herring, J.D. (Jim)]

Dear Irene,

If your research question is whether there is a difference in global mean field power between conditions I would approach this in the same way as if you would want to investigate a difference in ERF/ERPs between conditions. You would therefore first calculate the time-locked averages for both conditions for each participant separately, as you did. The you would calculate the global mean field power using ft_globalmeanfield for both conditions, for each participant. If I’m not mistaken you can calculate the group average using ft_timelockgrandaverage. You could test the difference between conditions using dependent samples t-tests (perhaps cluster corrected over time) using ft_timelockstatistics.

Best,

Jim

From: fieldtrip-bounces at science.ru.nl [mailto:fieldtrip-bounces at science.ru.nl] On Behalf Of Irene Sophia Mayer
Sent: Sunday, February 21, 2016 1:15 PM
To: fieldtrip at science.ru.nl
Subject: [FieldTrip] Global field power

Dear fieldtrippers,

I want to compare the global field power in two different conditions over several participants. I have computed time-locked averages for both conditions for each participant separately.

My first question now is, should I first compute a grand average over all participants and use

ft_globalmeanfield
on this or should I first compute global mean field for every participant and then average over them? Additionally, which functions should I use for those kinds of averaging?

The second question would be, has anyone any recommendations for a statistical test I could use to see whether the conditions differ in global mean field power?

Cheers,
Irene
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