Dear Markus,
> 1) I'm doing a mini block design in an (actual) event-related paradigm,
> because, as we have trials of
> about 3 seconds consisting each of a serial of
> cue-pause-stimulus-response window, it's not possible
> to model cue and stimulus separately and simultaneously (as they are
> correlated and the pause between
> them is always not more than 1200 ms). Am i right?
That's right. However, you can try to decouple them, if you run 'cue only' and 'stimulus only' trials, as well
> 2) If i am, would you suggest to skip slice timing (i know it's not
> necessary for blocks of bigger
> size, but these are real short ...and I am interested in the typical
> shape of the BOLD response in every condition,
> what would require slice time correction in an event-related experiment)?
It depends also on your selected TR (and/or TA), for short TR, it is less relevant than for long TR. In your case, the slice-timing correction could be useful.
> 3) The pause has got a variable extent of 900 to 1200 ms in order to
> yield a jitter and decrease expectancy.
> In spm2 i can only model constant block lengths (to my humble
> knowledge). So we thought about dropping time at the end
> of the longer blocks by modeling only blocks of a length of the shortest
> one. Could this be a problem for the statistics?
No, they don't need to have the same length. You can specify the duration of a trial for each trial separately, i.e. entering a vector of durations, having the same length as your SOA vector.
Good luck,
Karsten
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Karsten Specht, PhD
Department of Biological and Medical Psychology
& National Competence Centre for functional MRI
University of Bergen
Jonas Lies vei 91
5009 Bergen
Norway
Tel.: +47-555-86279
Fax: +47-555-89872
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http://fmri.uib.no/
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