Fwd: RE: clusterrandomization for 2 epochs separately

Olga Sysoeva olga at GRAPHICMIND.INFO
Wed Oct 22 13:10:01 CEST 2008

> Dear Eric, 
> I would like to consult with you about some our ERP data and
> application of the clusterrandomization to it. 
> I am writing now the article about ERP signs of visual change
> detection. 
> We have ERP to the "deviant" and "standard" stimuli sampling rate
> 512 Hz, 64 channels (Biosemi), 12 subjects. 
> If we use the paired-wise t-test to compare the ERPs' amplitudes in
> response to standard and deviant stimuli separately for each
> electrode and time point (and plot it see the picture at the end of
> the letter) we can see 2 (4) time regions of differences. But
> application of clusterrandomization analysis to these data (latency
> 0-500 ms) reveal only late cluster as significant, the early cluster
> is marginally significant (p=0.1). But I really believe in this early
> effect (120-160 ms), it is very important for our paper. When I run
> the clusterrandomization analysis on the narrowed epoch (0-300 ms) I
> got the early cluster significant. But the problem than that I loose
> the late effect, which is also worth mentioning in the paper. 
> Therefore, I would like you opinion about the possibility to use the
> clusterrandomization analysis separately on the 2 epochs of interest,
> let say first 250 ms post-stimulus (0-250 ms) and next (250-500 ms). 
> In this case there would be two significant clusters...  
> Best Regards, 
> Olga Sysoeva 
> P.S. 
> I also used different parameters for clusterrandomization (ndis,
> nchannels) but this does not change the results much.  
> P.P.S. 
> Additional material 
> The paired-wise t-test was used to compare the ERPs' amplitudes in
> response to standard and deviant stimuli separately for each
> electrode and time point. 
> The standard and deviant ERPs comparison reveals 2(4) intervals of
> significant differences:  
> Fig.1. At this weird J picture we see the boxes of significant
> differences between standard and deviant ERPs for each time point (x
> axis) and electrode (y axis). 
> Olga Sysoeva, PhD
> Institute of Higher Nervous 
> Activity and Neurophysiology
> Russian Academy of Sciences
> 5a Butlerova str.
> Moscow 117485
> tel.: (7-095)-3347011, 
> fax:(7-095)-338-85-00.    
> Links:
> ------
> [2] http://www.ru.nl/master/cns/

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