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Dear experts, sorry for another parametric modulation question, but here it is: my trial is the following: expectation period (reward cue: 3.75s) - target (0.75s) - outcome period (win/loss: 1.25s). 2x2 cue conditions and a (small) behavioral interaction between both factors for reaction times (RTs). i want to know whether the reaction time effect is reflected in activity of "motivating" brain areas, who should show activity throughout the expectation period. what i did: put all 4 cues in one regressor (0th) and included RTs as 1st order regressor in 1st level analysis. one-sample t-test on 2nd level - bad results :( so i'm looking for errors i made and these are my questions: a) is it wrong to model the cue period with a duration of 3.75 (not a stick) in a parametric modulation model? everytime i read about it, they take stick functions .... but i got nice results with mini-blocks in an earlier study. b) before entering RTs, i mean corrected them (which is done by spm5 anyway, which i learned later). as i'm looking for areas showing greater activation with decreased RTs, and since i thought the hrf is scaled (modulated) by RT values in its height, shouldn't i also invert values (meaning that e.g. -11,64s deviation from mean RT should be entered as +11,64s)? or will the [-1] contrast test for that opposite relationship on 2nd level (i thought it would only test for the absence of linear modulation ...)? c) in a discussion earlier in the list, Rik mentioned the possibility of additionally modelling categorial responses within such a model as +1 and -1 values in a second parametric regressor. what kind of order should i assign to that regressor - linear? thanks very much for your help Markus -- Dipl.-Psych. Markus Staudinger Social Cognitive Affective Neuroscience Group Department of Psychiatry Division of Medical Psychology University of Bonn Sigmund-Freud-Strasse 25 D- 53105 Bonn Germany Tel: +49 (0)228 287 19704 Fax: +49 (0)228 287 19125 E-mail: [log in to unmask]