Hi Serge
looks alright. As I understand your description, 'fixation' enters
implicitly as the experimantal rest condition and does not to be
modelled explicitly in the design. The contrast in your case is 1 1 1 0
0 0 -3 (as you want to look at A1-S + A2-S + A3-S)
cheers
Christian
Rombouts, S.A.R.B. wrote:
> Hi,
>
> Our mixed event-related / block design included the conditions A1, A2,
> A3, B1, B2, B3, S.
> Ax and Bx were presented randomly in 30 sec. blocks, followed by 30 sec.
> blocks of S
> Ax and Bx were pictures (x denotes a specific category): each was
> presented for a few seconds, followed by 1-3 sec. fixation. S was a
> scrambled picture (also always followed by 1-3 sec. fixation).
>
> I am interested in activation during all conditions versus S, and I
> defined 7 EVs (A1, A2, A3, B1, B2, B3, S), but I did not specify the
> short fixation after each picture.
>
> Hope this is ok so far.
>
> To calculate activation during A (both A1, A2 and A3) compared to S, I
> assumed the proper contrast is 1 1 1 0 0 0 -3.
> Is this correct or should it be 1 1 1 0 0 0 -1?
>
> Thanks a lot,
> Serge.
>
>
--
Christian F. Beckmann
Address: Oxford University Centre for Functional
Magnetic Resonance Imaging of the Brain,
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
Email: [log in to unmask] http://www.fmrib.ox.ac.uk/~beckmann/
Phone: +44(0)1865 222782 Fax: +44(0)1865 222717 Mob: +44(0)7811 189123
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