(1) You want A,B, and C in the same run. Otherwise, you might have
different baselines because the cognitive tasks are different.
(2) You always want null events or blank space between your events.
This is what creates jittering.
(3) A fourth task would probably be ideal (A-D) and (B-D), and (B-D)
and (C-D). It's hard to say what the control task should be though
without knowing the experiment.
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Postdoctoral Research Fellow, GRECC, Bedford VA
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Office: (773) 406-2464
=====================
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On Thu, Oct 13, 2011 at 11:19 PM, Tingting Wang <[log in to unmask]> wrote:
> Dear SPMers,
>
>
>
> Thanks for reading. I want to ask some questions about parametric design.
>
>
>
> In my experiment, I have three factors, A, B, and C. The aim of the
> experiment was to find whether certain common brain areas were involved in A
> and C (conjunction), or B and C (conjunction). During the experiment,
> participants were asked to rate the levels of A (or B, or C). However,
> factor A and B were correlated (A were male faces, and B were female faces).
> My questions were as following:
>
>
>
> 1) Since factor A and B were correlated, should I divide the three factors
> in to three runs? For example, in run1, participants judged factor A in four
> levels, in run2, participants judged factor B in four levels; and in run3,
> participants judged factor C in four levels. Is it doable?
>
>
>
> 2) Should I put null trials in each run? Is this necessary?
>
>
>
> 3) Since I want to make the conjunction of A and B, and B and C, I suppose
> that the motor response should be controlled. But I’m not sure which way is
> better: a) Counterbalance the responses between participants; b) Use a
> control task like “brightness rating task” as the fourth run. Could you give
> me some better suggestions?
>
>
>
> Thank you very much for your time and consideration. Look forward to your
> reply!
>
>
>
> Best wishes!
>
>
>
> Sincerely yours, Lisa
> Wong
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