Hi Anhuiyi,
To answer your questions.
-
The source localization is done on the same time basis as your epoch. If you epoch contains a pre-event part, e.g. starting 200 milliseconds before, the time-axis is negative there and zero is aligned with the event usually.
-
Indeed, eventually you want a Nsources X Ntime matrix, which you can make by multiplying a Nsources * Nchannels by a Nchannels * Ntime matrix. The Imaging kernel is a transformation that operates on your channel time series and transforms it to source time series.
I would not advice this, it is highly likely that Matlab doesn't take this since you are dividing a matrix by a vector, which gets you in all kinds of dimensionality problems. And doesn't take the dimension of time away.
What you could do is get the full time series of the sources and then average over the time axis with Source = mean(ImagingKernel*F,2), which would give you the average response of a source over time.
Kind regards,
Steven