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Dear list members, at the moment we are somewhat puzzled by the use of a parameter on the first level: we have 30 stimuli of decreasing intensity and model the hrf with an additional parameter coding the intensity. Looking at the model (see figure) we conclude, that the parameter seems to be centered and then convolved with the canonical hrf, thus in the middle of the session, the modelled amplitudes are near zero. However, this is not what we would like to test for... am I missing something? Is there a way to omit the assumed normalization of the parameter, in order to get decreasing amplitudes thrughout the session? Thanks for any help! Kai, regressors -- Dr. Kai Lutz Neuropsychologie Universität Zürich Binzmühlestrasse 14 Raum 4.D.03 CH-8050 Zürich Tel: +41-44-6357395 Fax: +41-44-6357409