Rik and Richard,
Many thanks for setting me straight re. SOA and TR.
>Thus I would use slice-timing correction for any TR between 0-3s.
My question here really is whether, although the slice timing works best at
lower TRs, there is some length of TR below which there is no practical
benefit of using it. In analysing some previous event-related data, I was
struck by how a relatively sizeable error (about a second) in specifying
when events occured, there seemed sufficient flexibility in the model to
cope with the timing problems. That is, when I accidentally modelled all
events as occuring (approximately) a second later than they actually did,
the resulting activations (modeled solely with canonical HRF wave) differed
little from the correctly modelled data. I assumed that this was a result
of a very blurred temporal reposnse and some degree of flexibility in the
way that SPM models the responses. This would suggest that the slice timing
correction, though working best at low TRs, has its least practical value
at these TRs. Does anyone out there have a feel for whether there is any
lower limit below which correction for slice timing has lost its value?
(I suppose this may be largely a hypothetical question as, even if there is
no clear benefit at low TRs, it behoves one to model the data as accurately
as possible).
Any advice gratefully recieved.
Paul Fletcher
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Paul Fletcher,
Research Department of Psychiatry,
University of Cambridge,
Addenbrooke's Hospital,
Hills Road,
Cambridge,
UK
CB2 2QQ
Tel 01223 336 988
Fax 01223 336 581
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