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

Russell Butler Russell.Buttler at USherbrooke.ca
Tue Oct 7 11:53:50 PDT 2014


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


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