Hello,
re. problem 1
Do I understand you correctly that you have specified NO variable durations
for both ON and OFF. This isn't true for your OFF phase and so I think it
would work if you specified yes for this one only and then entered your
vector (13 40 40 40 25). This has produced a rather pretty little design
matrix on my computer with different lengths of block for OFF
(Of course, judging by my response to the rapid event-related question,
it's probably best to take my advice with a large grain of salt)
Good luck
Paul Fletcher
At 01:54 01/12/00 +0000, you wrote:
>SPMers help!
>
>I am a new spm user, and I trying to come up with a fMri experimental model
>and contrast. Please see if my logic is at fault/imcomplete. I have tried
>your on line tutorials and mailing list archives.
>
>My experiment consists of on (stimulus) and off times. In terms of frames,
>the breakdown is
>
>Condition Frames length
>OFF 1-13 13
>ON 14-53 40
>OFF 54-93 40
>ON 94-133 40
>OFF 134-173 40
>ON 174-213 40
>OFF 214-253 40
>ON 254-293 40
>OFF 294-319 25
>
>My first problem is with the experimental model. I'm looking for a checkered
>pattern ie
>
>M
>M
>M
>M
>
>but have not achieved one when I fill SPM in as follows...
>
>Interscan interval 2.24
>scans 319
>trails 2
>SOA variable
>vector on 14 94 174 254
>vector off 1 54 134 214 294
>NO variable durations
>epoch lengths on 40
>epoch lengths off 13 40 40 40 25
>regressors 0
>
>PROBLEM, when I look at the fmri design for off, epoch lenth for off is
>13... not 13 40 40 40 25... Why is that....?
>
>Remedy... have three variables with the first being just 1-13 (off)
>The second being the on's
>The third being the rest of the off's
>
>
-----------------------------------------------------------------
Paul Fletcher,
Research Department of Psychiatry,
University of Cambridge,
Addenbrooke's Hospital,
Hills Road,
Cambridge,
UK
CB2 2QQ
Tel 01223 336 988
Fax 01223 336 581
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