Hello SPMers, I'm trying to run my first event-related experiment and
there's something not clear about SOA. Our experiment consists of
presenting visual stimuli.
There is a fixation point on the screen and randomly letters are presented.
Each letter lasts for 2 seconds.
Letters can be divided in two groups: CONGRUENT and INCONGRUENT.
Processing data with spm99 I think I can put:
- number of conditions or trials: 2 (baseline (fixation point) not included)
- stochastic design= no
- SOA= VARIABLE- vector of onset (scans)-trial 1= the onset for every
CONGRUENT letter appearence
- SOA= VARIABLE- vector of onset (scans)-trial 2= the onset for every
INCONGRUENT letter appearence
- VARIABLE DURATIONS= ??????????????? I think is no because every letter
lasts 2 sec.
I'm not sure about this last point because if I say NO, how the program can
know how long is the stimulus?!?
And if I had INCONGRUENT letters of different durations each one, how could
I tell the program because even if I say yes to the VARIABLE DURATIONS, the
program should ask me the length of every trail but not the length of every
letter?!?!?!!?
I really thanx everyone can help me in any way. Bye Marcello
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