SPM Design Matrix
SPM design matrix contains information about the time courses and onsets for the
regressors. Multiple regression and correlation sorting criteria in GIFT use SPM
design matrix to sort components temporally. The SPM design matrix filename
selected is in .mat format. Type load filename at the MATLAB command prompt to
view the SPM structure. GIFT uses the following fields in SPM structure:
- nscan
- Refers to the number of scans. For multiple sessions, nscan should
look be a row vector like [110 110 ... 110].
- xX.X
- Contains regressor time courses of dimension m by n where m is sum of
scans over sessions and n (length of SPM.xX.name) is number of
regressors.
- xX.name
- Contains the regressor names in a cell array. Number of regressors is
equal to length of cell array.
- xY.RT
- Refers to the repetition time (TR).
- xBF.UNITS
- Refers to units in seconds or scans.
- Sess
- Contains information like onsets. Length of SPM.Sess is equal to the
number of sessions (length of SPM.nscan).
How SPM structure should look like for one session and multiple sessions are
discussed below:
- One Session
- SPM.nscan should be a number. Length of SPM.Sess structure should be
one.
- Multiple Sessions
- SPM.nscan should be a row vector or a single number equal to the sum
of SPM.nscan. Length of SPM.Sess should be equal to length of SPM.nscan.
Note: GIFT pulls session specific regressors only when the
regressor names contain the session number like Sn(1)
right_visual_hemisphere*bf(1) where 1 after Sn( refers to the session number.