Dear Michael,
> These latter two contrasts give considerably
> different SPMs compared to the ones that isolate a single effect. This
> combination of results suggest to us that the [1 -1] and [-1 1]
> contrasts may be more sensitive to relevant task
> associated changes than a more typical contrast settings used for
> event-related experiments? Does this make statistical sense, and are
> there any published methodological references which document and further
> describe such a phenomenon?
Yes, in general the sensitivity of an event-related design to different
contrasts will vary as a (complex) function of SOA, event ordering and the
presence of null events. Relevant refs are:
Friston, K.J., Zarahn, E., Josephs, O., Henson, R.N.A. & Dale, A.
(1999) Stochastic designs in event-related fMRI. Neuroimage, 10,
607-619.
Josephs, O. & Henson, R.N.A. (1999) Event-related functional
magnetic resonance imaging: modelling, inference and optimization.
Philosophical Transactions of the Royal Society, B, 354, 1215-1228.
If you search the list archive for 'event related efficiency' or
'optimisation' there are also details of the MGH seqefficiency program and
further discussion of this topic.
Best wishes,
Geraint
--
Dr. Geraint Rees
Wellcome Advanced Fellow, Lecturer,
Division of Biology 139-74, Institute of Neurology,
California Institute of Technology, University College London,
Pasadena CA 91125 London WC1N 3BG
voice 626-395-2880 020-7833-7472
fax 626-796-8876 020-7813-1420
web http://www.klab.caltech.edu/~geraint
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