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Hi Ekarin, If you read my 2012 paper on generalized PPI, you can absolutely model 4 Condition EVs, 4 PPI EVs, and the physiological EV. If you model each condition separately, then you will have much more freedom on the contrasts that you can generate. There is also a nice paper, with video, for doing this in FSL (Harrison et al., 2017; https://www.ncbi.nlm.nih.gov/pubmed/29286444) Best, Donald Best Regards, Donald McLaren, PhD On Mon, Mar 19, 2018 at 12:18 PM, Ekarin Pongpipat <[log in to unmask]> wrote: > Thank you, Anderson! I was able to figure out the convolution part. > > For the linear contrast question: > Rather than making a model with 4 EVs of cond1-control, cond2-control, > cond3-control, and cond1+cond2+cond3+control > > Would it be appropriate to make the following EV? > Linear: -1.5*control - 0.5*cond1 + 0.5*cond2 + 1.5*cond3 > > If so, would it need to include the following EVs as well to make it > complete? > Average: .25*control + .25*cond1 + .25*cond2 + .25*cond3 > Quadratic: -.5*control + .5*cond1 + .5*cond2 - .5*cond3 > > I hope this is more clear. > > Thank you again!, > Ekarin > > On Sun, Mar 18, 2018 at 4:21 PM Anderson M. Winkler < > [log in to unmask]> wrote: > >> Hi Ekarin, >> >> Please see below: >> >> >> On 12 March 2018 at 13:58, Ekarin Pongpipat <[log in to unmask]> wrote: >> >>> Hi FSL experts, >>> >>> I had several questions about creating the PSYCH term (i.e., a contrast; >>> https://fsl.fmrib.ox.ac.uk/fsl/fslwiki/PPIFAQ). If I have four related >>> stimuli conditions in a block-design, is it possible to make the following >>> contrasts within the same model: cond1-control, cond2-control, >>> cond3-control? >> >> >> Yes, create these 3 EVs with the differences, and include a 4th EV that >> is cond1+cond2+cond3+control. >> >> >>> Would it be appropriate to convolve this contrast? >> >> >> >> Yes, it is appropriate to do the convolutions on these EVs (not >> contrasts) before or after the subtractions, and also multiply by the >> physiological measurement. >> >> >> >>> If so, how would you determine the duration of the convolution (note: >>> block duration for cond1, cond2, and cond3 are the same but the block >>> duration for control is much shorter). >>> >> >> I don't understand this question. >> >> >>> >>> In a different PPI model, is it possible to model the PSYCH term as a >>> linear contrast? If so, would I need to also include an average and >>> quadratic contrast to make the model complete? And similarly, would the >>> convolution be appropriate here as well? >>> >> >> I don't understand this question either, sorry. >> >> All the best, >> >> Anderson >> >> >>> >>> Thank you!, >>> Ekarin >>> >> >> -- > Ekarin E. Pongpipat, M.A. > Ph.D. Student in Cognition and Neuroscience > Cognitive Neuroscience of Aging Laboratory > Center for Vital Longevity > School of Behavioral and Brain Sciences > The University of Texas at Dallas > [log in to unmask] >