Dear SPM community,
I know these issues have been adressed before, but I am still not sure how to deal with
a particular problem.
I want to compare trials with variable durations due to different delay periods (2.5s vs.
6.5 s).
After convolution with the hrf the regressors for these two trials habe different
amplitudes which results in much higher beta-values for the short compared to the long
trial. If I want to compare both conditions at the second level, the chance that I get
significant activation for the comparison short-long is much higher the for the
comparison long-short.
I think what I want instead is to compare the integrated amount of activity between both
trials. Is there any way to do this?
Or is it possible:
1) to scale the regressors to have an equal amplitude?
2) to scale the con-images after the first level analysis?
3) any other idea or theoretical consideration?
4) Please let me know if I am completely off track
Thank you for your help,
Claudia
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Claudia Preuschhof
Berlin NeuroImaging Center
Charité Campus Mitte
Department of Neurology
Schumannstr. 20/21
10117 Berlin, Germany
Phone: ++49-30-450 560 195
Fax: ++49-30-450 560 952
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