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Dear all I’m trying to design an event related fmri experiment using the optseq software (http://surfer.nmr.mgh.harvard.edu/optseq/). My paradigm is an instrumental learning task (attached figure). There are three types of trials: reward, neutral and loss trials. On the reward trials two pictures are presented; the participant has to select one of them and depending on the option an screen appears indicating that the participant “wins” something or gets “nothing”. Neutral and loss trials work in a similar way but the outcomes are either “no change”/ “nothing” or “loss”/ “nothing” respectively. I’m planning to analyse this task with an event related design considering two time points from each trial (the initial time when the two pictures are presented and the outcome time) plus a parametric modulation for each time point. Therefore, for each type of trial (reward, neutral, loss) I’ll have four columns in my design matrix (the two event onset columns plus the two parametric modulation columns). In total, the design matrix will have 12 columns. I’m not sure how to run the optseq in order to properly optimize this experiment. Shall I enter three types of events (reward, neutral, loss trials)? In this case the duration of each event would be the total trial length (from the time that the two pictures are presented to the time of the outcome plus a minimum inter-trial interval) Or is it important for optseq to distinguish the trials according to the outcome? This means, do I have to distinguish as different event types the reward trials where the participant “wins” something from the ones where the participant gets “nothing”? (and similarly for the neutral and loss trials). If this is the case, then I am not sure how to proceed with the optseq since I don’t know how many “reward-win” and “reward-nothing” trials I’ll have given that this is dependent on the participant’s actions. I’ll be very much thankful for any kind of help with this issue. Victoria Victoria Gradin Research Student Clinical Research Centre Dept. of Mental Health University of Aberdeen Royal Cornhill hospital Tel: 01224 557972 The University of Aberdeen is a charity registered in Scotland, No SC013683.