[FieldTrip] Localizing phase-locked or non phase-locked gamma

russ port russgport at gmail.com
Sat Dec 31 05:49:04 CET 2016

Hi Fieldtrippers,

I have a quick question - which has been hinted at many times on the mailing list - but I think a solid answer could be quite beneficial to the community (or may be just me, and I’m being overly thick). Currently I have two procedures I am analyzing. One is a auditory steady state response (40Hz amplitude modulated 500Hz tone). The other is a visual gamma paradigm (produced via a standard black/white grating). For the auditory task, we are interested in localizing phase-locked activity. For the visual gamma we are infestered in localizing non phase locked activity. I initially (for reasons uninteresting to this discussion) tried to do this via LCMV’ing (getting  at the different forms of activity based on previous posts about whether to build a covariance matrix based on the data [all trials] or the average ERP). Hopefully, I am starting to see the light, and realize that I should be using something more akin to DICS. How (or is it even possible) can I have the DICS source localization choose which form of activity (phase- or not phase-locked) I am interested in? Is it just as simple as passing the time frequency output of ft_freqanalysis for either the ERP (for phase locked activity) or all trial data (for phase and non-phase locked activity), similar to used when typically generating TF plots?

To Long, Didn’t Read: Previous posts on the listserv suggested that for LMCV beamforming, you could selectively go after phase locked or time locked but all phase signals (i.e. akin to total power) based on how you built the covariance matrix (on the ERP or non averaged data respectively). A) Is this true? B) when using DICS to go after phase locked activity or total power, can you simply just use the time frequency output of ft_freqanalysis that you would for plotting TFs of either phase-locked (evoked) or total power?

Russ Port 
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