[Eeglablist] Random selection of trials

[Digavalli, Siva]

Hi Kris
Unequal averaging was a concern for us as well in a rodent protocol. What we did was to identify the standard trial preceding the "odd ball" and use that to make an average. That way, you will have the same number of oddball and standard trials, contiguous in time.  I do not use EEGLAB for this and do not know how to accomplish this. I am sure someone else on this forum might be able to. Good Luck!
Siva

>-----Original Message-----
>From: eeglablist-bounces at sccn.ucsd.edu [mailto:eeglablist-
>bounces at sccn.ucsd.edu] On Behalf Of Kris Baetens
>Sent: Wednesday, March 31, 2010 11:04 AM
>To: eeglablist at sccn.ucsd.edu
>Subject: [Eeglablist] Random selection of trials
>
>Dear colleagues,
>
>We employ a paradigm which inherently leads to a different number of
>trials in both our conditions (oddball-like). We have two conditions,
>one with an average of about 150 trials, the other with about 1500
>(artefact-free).
>
>- Does anybody have research to support my concern that comparing both
>conditions with the total number of trials may lead to artificial
>effects due to the different number of trials (and associated variance
>and "cleanliness" of the gavg's)? (I have seen such things published
>before.)
>- Does anybody know of an easy way to make a random selection of a
>predetermined number of trials out of the total number in EEGLAB or
>MATLAB? (Which would allow for selecting an equal number of trials in
>both conditions.) Obviously, we don't simply want to take the first or
>last 150 regular trials, since this would possibly lead to erronous
>conclusions.
>
>Thank you very much in advance,
>
>Kris Baetens
>Ph.D. fellow of the Research Foundation - Flanders (FWO)
>Dept. Experimental and Applied Psychology
>Faculty of Psychology and Educational Sciences
>Vrije Universiteit Brussel
>
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