I'm trying to plot maxima from ROI coordinates, and am having a difficult
time understanding the results. I thought I understood what information the
maxima provided me with...but I think I'm not entirely sure of the functions
that go into calculating the maximas, because the results aren't exactly as
I expected them to be. Any help would be much appreciated.
I'm running a flexible factorial model with two variables: subject (30
subjects) and trialtype (4 trialtypes). So I have 34 columns in my design
matrix: 30 subject columns, followed by the 4 trialtypes.
I pick a t-contrast (for instance, positive trials > negative trials), plot
the maxima, and extract the fitted Ys.
Normally I would expect to receive 30 values, one for each participant. But
I'm getting 120 values...which I assume is 30 x 4, or one for each trialtype
My real confusion, however, lies in the fact that if I pick a different
t-contrast (negative trials > positive trials, for instance), and extract
the maxima from this image...I get a *different* 120 values.
This makes me think that my initial interpretation of the 120 fitted-Ys as
representing the maxima for each trialtype per subject is in error...because
if that were the case the values should be constant across all contrasts.
And so: can someone help me understand what information is being provided
when I ask for the fitted-Ys? What do each of the 120 values represent?
Thanks in advance,
Matthew S. Shane
The Mind Research Network
[log in to unmask]