Dear SPMers,
I have been running an event-related fMRI study in which a single
stimulus is presented once every 16 seconds. In this study, there are 2
factors, each with two levels. Thus, there are 4 conditions, with 40
trials per condition. The study involves a Stroop analog and the main
comparison is between congruent and incongruent Stroop-like stimuli.
In looking at the data from 10 subjects, I haven't been seeing
much activation for this main effect (for which there are 80 trials per
condition). However, relative to baseline, individual trial types (e.g.,
consistent and inconsistent trials) are producing lots of activation.
But, the activation appears to be similar for consistent and inconsistent
trials.
My question is: are 40 trials per condition (80 when computing
main effect of consistency) generally too few to see significant results
in 10 subjects?
Thanks,
:> Daniel Weissman
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