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Would you please tell us what you did to create your regressors and tell us which regressors are different between the two models?

Regressors are based on the onsets times, durations upsampled to the number of time bins convolved with the HRF from spm_get_bf. They are then downsampled to the TR. Regressors are not demeaned, or orthogonalized. Derivatives are orthogonal based on the basis functions being orthogonal. Parametric modulators are demeaned before forming the PM regressor.

Stimulus time -- if in the time bin the stimulus is present, its coded as 1. This vector of stimulus times is convolved with the HRF.

In SPM, the data is also scaled to a global mean of 100.

There are also potentially filters and autoregressive terms as well.


Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Wed, Nov 13, 2013 at 9:48 AM, Elsa Fouragnan <[log in to unmask]> wrote:
Hi,

While entering my own design matrix, containing regressors of interest and non-interest in SPM using the entry "multiple regressors" in the batch (model specification) I obtain results that are partially different than what SPM would have produce if the regressors would have been input in the standard way. Would it be possible to know exactly all the SPM steps in this part of the analysis (e.g. the hrf function used, how the stimuli function is created, how regressors are created, demeaned and orthogonolized..).

Thanks a lot,

Elsa