[Eeglablist] newtimef ersp output without any or with external baseline
Andero.Uusberg at ut.ee
Thu Feb 25 13:03:15 PST 2010
I have a few (maybe fairly naive) questions regarding running the
newtimef function without using baseline from the dataset being analyzed.
Firstly, while running newtimef on a channel of a segmented dataset
without either of the baselines (having both 'baseline' and 'powbase'
set to NaN) I have trouble understanding the units of the output ersp
matrix (I call the function from the command line and use freqrange
2:20, padratio 2, cycles 1 6 and basenorm 'off'). The output ersp matrix
is full of positive numbers in the range of 40 to 60. Although the
figure legend states this is 10*log10 transform of power density in
microvolts, this does not seem likely (the power densities would be
around 100 000 microvolts). In addition, even with both baselines set to
NaN the powbase output is created (consisting of numbers in the same
range). All this probably has something to do with the normalization
process and is completely meaningful, but could someone explain how
exactly these values are generated and what is their unit?
Second and related question regards feeding externally created baseline
into newtimef via the powbase key. I know one way would be to calculate
the basline with newtimef in the first place and not to care about the
units of the data :) However, I would also like to be able to use data
calculated with FFT in Vision Anlayzer as the baseline. Do I understand
correctly that the data should be in power denisty units (square of
microvolt per hertz) and should I run the 10*log10 transform on the data
before feeding in into the newtimef with powbase?
Finally, as I'm not sure my previous e-mail reached the list I repeat a
related question concerning using std_precomp for calculating ERSPs for
several datasets using a single external baseline. When referring to a
channel-by-frequencies (as well as frequencies-by-channles) matrix of
external power density values with the powbase key in erspparams field
og std_precom, I receive the following error message: "std_ersp at 372:
powbase should be of size (ncomps,nfreqs)". Can anyone estimate if this
could be a bug or should I keep figuring out what I'm doing wrong?
I apologise if these issues have been dealt with before in the list in
which case I am grateful for a kind reference to older posts.
With kind regards and general gratitude to eeglab :)
University of Tartu
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