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Hi Joshua, I guess, you are still using the high-pass filter, isn't it? That will cause these extra values. Good luck, Karsten *Von:* "Joshua Goh" <[log in to unmask]> *Gesendet:* 04.05.09 22:47:29 *An:* [log in to unmask] *Betreff:* [SPM] FIR Design Matrix Dear SPM Users, I am trying to implement an FIR analysis on my event-related data and was puzzled by the resulting design matrix output. I performed the first-level analysis using the FIR basis function. TR = 2s, window length = 18s, Order = 9, no other parameters were changed. The resulting design matrix looks like FIR_X_autocorrelation (attached and shown below). I am puzzled why the design matrix isn't composed of simple diagonals for each trial, but seems to have some temporal derivative incorporated into the later delta functions. (FIR_X_autocorrelation.png src="https://img.web.de/web/img/v4/p.gif) I therefore tried the same thing again but without AR(1) to correct for serial correlations, and the resulting design matrix looks like FIR_X_noautocorrelation (attached and shown below). This looks much better, obvious clean diagonal matrix, but still, there seems to be negative modeled values in the later orders for each trial. Does anyone know what these "extra" values are? Am I missing some assumptions in the way SPM creates an FIR design matrix? (FIR_X_noautocorrelation.png src="https://img.web.de/web/img/v4/p.gif) Any help would be greatly appreciated. Thanks, Josh Goh -- ------------------------------------------------------------- Karsten Specht, PhD Department of Biological and Medical Psychology & National Competence Centre for functional MRI University of Bergen Jonas Lies vei 91 5009 Bergen Norway Tel.: +47-555-86279 Fax: +47-555-89872 [log in to unmask] http://fmri.uib.no/