[FieldTrip] Precisions on DICS beamforming on EEG data and using normalisation

[MP Coll]

Dear Fieldtrip Community,

My name is Michel-Pierre Coll and I am a postdoctoral researcher at 
King's college London.

A reviewer recently suggested we perform DICS beamforming to source 
localise EEG effects in the frequency domain during an action 
observation/execution paradigm. I was able to perform these analyses 
using the very good tutorial on the Fiedltrip website. However, I have 
some questions regarding these analyses. I have searched the literature 
and the mailing list but somehow I can't find clear answers to these 
basic questions.

1) Is it appropriate to perform DICS beamforming using EEG with 60 
channels (standard montage) ? If not, what would be the appropriate 
number of channels ? Can you suggest a reference discussing this issue ?

2) When not using a contrast to perform the beamforming, is the 
normalisation of the lead field an adequate procedure to correct for the 
depth/centre bias ? The Fieldtrip tutorial suggest it is but other posts 
on the mailing list suggest that it is not.

3) How does one choose an optimal time window for DICS beamforming when 
the duration of the effect is quite long (e.g. several seconds of alpha 
changes in response to a visual stimulus) ? Is it correct to use a 
longer time-window (e.g. 2 seconds) that is representative of the 
duration of the effect ?

I would greatly appreciate any hints on these questions or if you could 
point me towards relevant texts discussing these issues.

Best,
MP Coll