Dear SPM-List
I am an fMRI newbie and currently working on my first fMRI study as part
of my doctorate.
I am conducting a simple event-related task where participants have to
push a button whenever a letter "other than X" appears on screen while -
in all other trials - an X appears on screen (each stimulus is presented
for 750 ms). These letters are superimposed on a video which changes
halfway through the task (we therefore have the conditions X/Non-X //
Video1/Video2 (which appear in a counterbalanced order).
I have now estimated my 1st-level models and - comparing Xs and Non-Xs
in the different conditions, I do encounter an orthogonality issue in
that collinearity is extremely high.
Is there anything to specify differently that might help with this
problem (I have already increased the high-pass filter)?
Any help would be appreciated.
Many thanks
Benjamin
____________________________________________
Benjamin Boecking
Department of Psychology, P077
Institute of Psychiatry
King's College London
De Crespigny Park
London SE5 8AF
UK
phone: +44 20 7848 0389
e-mail: [log in to unmask]
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