Dear Jack,
If I understand the design correctly, the two are equivalent but in either
case there is a problem of rank deficiency when trying to model attention
(since it is present in both of the two conditions). Are there also blocks
of baseline such as rest, fixation, whatever that are not being
modeled? If not, the effects of attention are not distinguishable because
there is no experimental variation.
Another way to think about it is if there are only two blocked conditions,
you only need one binary variable to model them (ie 1 EV).
Hope this helps.
Joe
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Joseph T. Devlin, Ph. D.
FMRIB Centre, Dept. of Clinical Neurology
University of Oxford
John Radcliffe Hospital
Headley Way, Headington
Oxford OX3 9DU
Phone: 01865 222 738
Email: [log in to unmask]
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