Dear Priyantha,
>dear all,
>
>I have been trying to use the adj means/fmri button to collapse my
>fmri data with the intention of using the summary data in a second
>level analysis.
>However, as usual, i could not figure out how to do this!
>i am asked for the epoch order within the session.. which is OK. let
>us say i have 5 conditions within a sessions such that
>RACBRDCER where R is rest A, B, D, E are task blocks and C is
>another base line. For each block I have 6 functional volumes. I get
>in to trouble when I start filling in the number of volumes per
>condition.. it goes on and on and on... how come?
>Can somebody please spend a little time and explain to me how to
>do this properly?
>
I don't really know why you are having problems. Lets say you have selected
54 scans and enetered the string above (RACBRDCER), it should then be
possible for you to specify 6 when asked for #scans/Epoch. If on the other
hand you had selected e.g. 51 scans (e.g. because three first were dummy
scans) you would then need to specify the length separately for each epoch,
i.e. 3 6 6 6 6 6 6 6 6. Hence my only possible explanation for your problem
is if the number of epochs you specify multiplied with the #scans/Epoch
don't equal the no. of scans you selected.
Having said that I would strongly recommend using con*.img from the first
level analysis for your second level analysis rather than using the AdjMean
function. You should create your contrasts at the first level testing them
with a one-sample (or two sample if you look for group-by-contrast
interactions) t-test at the second level. Taking the condition means to the
second level enetering them into a PET type analysis potentially inflates
your type I errors since you then implicitly assume that the inter-subject
variablility in activation to one task tells you something about the
inter-subject variablility in activation to another, which is pretty
unlikely to be true.
>Thanks a lot,
>
>
>
>Priyantha Herath MBBS
Good luck Jesper
Jesper Andersson
Wellcome Dept. of Cognitive Neurology
12 Queen Square
London WC1N 3BG
phone: 44 171 833 7484
fax: 44 171 813 1420
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