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 ===================== This e-mail contains CONFIDENTIAL INFORMATION which may contain PROTECTED HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED and which is intended only for the use of the individual or entity named above. If the reader of the e-mail is not the intended recipient or the employee or agent responsible for delivering it to the intended recipient, you are hereby notified that you are in possession of confidential and privileged information. Any unauthorized use, disclosure, copying or the taking of any action in reliance on the contents of this information is strictly prohibited and may be unlawful. If you have received this e-mail unintentionally, please immediately notify the sender via telephone at (773) 406-2464 or email. 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 >