Dear Steve,
> Once I've created a design (in my case, a stochastic design), I assume
> I'm encouraged to use the design created by SPM to implement my actual
> stimulus trains. The "explore design" interface is a nice overview,
> but it's too small to pick out the numbers. I can always just look at
> the appropriate data structures in SPM_fMRIDesMtx.mat, but is there an
> easier way to do it?
No, the easiest way is to use the data in the structures. These structures
are described in the help filess, e.g.
>> help spm_fMRI_design
Assembles a design matrix for fMRI studies
FORMAT [xX,Sess] = spm_fMRI_design(nscan,RT)
nscan - n vector {nscan(n) = number of scans in session n}
RT - intercans interval {seconds}
xX - structure describing design matrix
xX.X - design matrix
xX.dt - time bin {secs}
xX.RT - Repetition time {secs}
xX.iH - vector of H partition (condition effects) indices,
xX.iC - vector of C partition (covariates of interest) indices
xX.iB - vector of B partition (block effects) indices
xX.iG - vector of G partition (nuisance variables) indices
xX.Xnames - cellstr of effect names corresponding to columns
of the design matrix
Sess{s}.BFstr - basis function description string
Sess{s}.DSstr - Design description string
Sess{s}.rep - session replication flag
Sess{s}.row - scan indices for session s
Sess{s}.col - effect indices for session s
Sess{s}.name{i} - of ith trial type for session s
Sess{s}.ind{i} - column indices for ith trial type {within session}
Sess{s}.bf{i} - basis functions for ith trial type
Sess{s}.sf{i} - stick functions for ith trial type
Sess{s}.ons{i} - stimuli onset times for ith trial type (secs)
Sess{s}.pst{i} - peristimulus times for ith trial type (secs)
Sess{s}.Pv{i} - vector of paramters for ith trial type
Sess{s}.Pname{i} - name of paramters for ith trial type
...
For example, after loading the appopriate .mat file, typing
Sess{2}.ons{1} in the command window will give you the onset times (in
seconds) for the first trial type in the second session. This nvector
can now be used for stimulus design.
Merry Christmas - Karl
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