Please pardon a long-winded newbie question. I have a study where seven
subjects were scanned 8 times, twice in each of 4 mood conditions: rest,
induced negative mood, induced positive mood, and induced neutral mood.
The order of presentation of the mood conditions was randomized across
subjects (with the caveat that the two presentations of each mood condition
were adjacent). In each condition, subjects rated their mood (essentiallly
how positive or negative it was).
I have already done the straightforward subtractions comparing the
different mood conditions. However, this approach implicitly assumes that
each subject reacted identically to the mood manipulation conditions, which
isn't the case. What I would like to do is, instead of treating condition
as a categorical proxy for mood, to correlate activity with the mood
ratings directly.
To do this, I have used "Multiple subjects: covariates only", selecting the
images of each subject, and then entering the 56 ratings (7 subjects X 8
conditions) as a single covariate vector (with the ratings corresponding to
the appropriate image, of course). But from here I'm a bit flummoxed as to
what would be the appropriate settings for the other options. I'm also
assuming that specifying 1 for the contrast to get positive correlations
and -1 to get negative correlations is what I want, but I'm not sure.
My apologies for what I am sure are simple questions.
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