[Eeglablist] mean(single trial newtimef) != newtimef(all trials)

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Tue Oct 7 13:49:43 PDT 2014

Dear Ramon,

This report has a detailed description of the problem... could you
replicate it please?


On Tue, Oct 7, 2014 at 11:53 AM, Russell Butler <
Russell.Buttler at usherbrooke.ca> wrote:

> Hello, i've noticed a discrepancy between the two modes of calculating
> ersp in eeglab where i believe there should be no such discrepancy. i'm
> referring to the function newtimef, which can be run on single trials, or
> on a vector of trials.
> when i call newtimef with my vector of trials (ie, sending all trials at
> once to the function), i get back a nice mean ersp of all my trials, with
> most of the points in my baseline period coming out around zero.
> however, when i compute the newtimef on a single trial basis, and then
> average the results, i get my baseline period as being around -2db, and all
> other values are shifted 2 db to the negatives as well (ie, when i send all
> the trials at once to newtimef i get an ersp of around 4db in the task
> period, but when i compute single trials, and then average, i get an ersp
> of around 2db in the task period).
> i've tried playing around a bit with the arguments, ie, using the
> 'trialbase' argument, but it doesn't change anything.
> i need these single trials for my anovas, but i have to be sure that i'm
> actually computing them correctly...does anyone know how i can correct this
> systematic under-estimation due to averaging of the single trial ersp?
> thanks
> Russell
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Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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