Dear Ben,
this should give you the almost the same results, as long as you use contrasts that sum up to '0'.
The only difference is that you in a way overspecify your design and you loos one df.
Good luck,
Karsten
--
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Karsten Specht, PhD
Department of Biological and Medical Psychology
Bergen fMRI group
University of Bergen
Jonas Lies vei 91
5009 Bergen
Norway
Tel.: +47-555-86279
Fax: +47-555-89872
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http://fmri.uib.no/
-----Ursprüngliche Nachricht-----
Von: "Ben Becker" <[log in to unmask]>
Gesendet: 12.okt.2011 15:43:26
An: [log in to unmask]
Betreff: [SPM] implicit baseline vs. explicitly modelling the baseline
>Dear SPMers,
>
>I'm analyzing a blocked design fMRI task with three conditions (a, b, c). The blocks are seperated by a fixation cross which serves as a low-level baseline (bl).
>My question:
>Is there a difference in the analysis on the first level when I model the low-level baseline explicitely as a regressor?
>That means: do the following contrasts differ?
>
>a) explicit modelling of the baseline
>regressors:
>bl a b c
>contrast: a > bl
>-1 1 0 0
>
>b) "implicit" baseline
>regressors:
>a b c
>contrast a > implicit baseline
>1 0 0
>
>Thanks in advance & best regards,
>
>Ben
>
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