[Eeglablist] Random selection of trials

Kris Baetens Kris.Baetens at vub.ac.be
Fri Apr 2 02:39:51 PDT 2010

Hi all, 

I would like to start by thanking everybody for their kind input and time. (For completeness' sake, I 
should note that in the numbers of regulars and deviants, only those were included that followed a 
regular in the first place, as some people voiced concerns about this.)

Some comments:
@ Tim curran: I have read Luck's book and I clearly see why using different trials in case of 
peak measures (which we do not use) might be problematic. However, I can't quite understand why 
average amplitudes would be 'immune' to this sort of problem; I think sensitivity to this 
problem decreases as the number of time points in your average window increases? (In extremis:
an average amplitude of two time points would, in the same logic as he discribes, still be extremely 
vulnerable, no?) 

@ Bradley Voytek: Thank you very much for the idea and the example script. We use a similar method
for difference testing between conditions as outlined by Maris en Oostenveld (2007) and are rather 
pleased about the results. 

@Arnaud Delorme & Matt Mollison: Many thanks for the input. I am relatively new to both eeglab and matlab, 
and even though I have found it is possible to achieve a rather steep learning curve with some effort, it
would probably have taken me hours to figure this out by myself. 

@Philip Michael Zeman: All in all, you formulated my concern rather accurately ("...you might have a 
distribution of values in condition 2 that are tightly distributed around the mean for the condition 
compared to in condition 1 that has a distribution of scores that are spread by a large 
amount around the mean of the condition.") However, selecting the first 150 of each kind of trial
doesn't seem an option; in the case of the "regulars", these would all be from the first minutes of 
the recording, whereas in the other condition they would be spread out over the entire recording. 
Whereas there are clearly issues with learning mechanisms, I cannot assume that learning in
the one condition is independent of the other (regulars follow an implicit sequence, whereas regulars
deviate from the same sequence. Both require "knowledge" of the same sequence.)

@Siva Digivalli: The solution you (and others) suggested, seems the most elegant/easy to implement. 


Ph.D. fellow of the Research Foundation - Flanders (FWO) 
Dept. Experimental and Applied Psychology
Faculty of Psychology and Educational Sciences
Vrije Universiteit Brussel
Pleinlaan 2, 1050 Elsene 
+32 2 629 23 31

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