[Mne_analysis] TFCE parameters

[Cushing, Cody]

Ah, alright beautiful.  Thanks for the explanation Eric.  I'm imagining using a start of 2 on a whole brain analysis would not make much of a difference, which I'm imagining is where that number was coming from.

Cheers,
Cody
________________________________
From: mne_analysis-bounces at nmr.mgh.harvard.edu [mne_analysis-bounces at nmr.mgh.harvard.edu] on behalf of Eric Larson [larson.eric.d at gmail.com]
Sent: Monday, July 18, 2016 3:38 PM
To: Discussion and support forum for the users of MNE Software
Subject: Re: [Mne_analysis] TFCE parameters

Is there any motivation behind start>0 other than trying to reduce computation time?

Not as far as I know.

Why are these the 2 parameters we have control for TFCE?  What's to be gained/lost?

Think of it as a way to approximate an integral where each function value to put into the summation takes a long time to compute (the clustering step). Ideally we would start at zero and go in infinitesimal steps to the largest statistic value, but numerically that's infeasible and practically it would take forever. So the idea is to compute as few as possible (highest start and biggest step) without affecting the result. If using a smaller start and/or step affects the output, then you should use the smaller start and/or step because it should provide a better approximation to the integral. Without looking back, I would assume a start of 2 was suggested because it usually doesn't affect the result (at least in the suggester's experience).

Eric

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