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Hi Amitai > Hi Cyril, > > There was a recent paper, in neuroimage I think, where RT of each > trials was used to model the hrf (instead of 0 modeling an > inpulse) and this model was compared with a standard approach (1 > column for the regressor + modulation by RT) -- clearly it was > better to directly 'modulate' the 1st regressor, but it may not > always be possible to do so .. cannot think of anything else here ... > > > I would love to get the reference for the paper you mentioned if you > happen to have any more information about it. Dorian pointing me the paper I was referring to Grinband et al, Detection of time-varying signals in event-related fMRI designs, NeuroImage, Volume 43, Issue 3, 15 November 2008 (http://www.sciencedirect.com/science/article/B6WNP-4T77G33-4/2/cc5ef4a8e9fbff5b4a99bd5f05663bf9) > Also, when the discussion is raised over the use of variable duration > HRF and utilizing an RT regressor, they are generally suggested as > alternatives to one another. Is there a concern regarding the use of > both of these in unison (i.e., modeling the HRF with trial-specific > RTs and then regressing out RT before adding additional parametric > regressors)? > well you would model the hrf using RT so that it accommodates natural cognitive and motor related variations in the neural dynamic - of course you may loose some info regarding the sensorial/perceptive processing which would not vary according to this.. - anyway; now you try to regress out RT for each trial - how would you do that? even if you could, what would that mean? remember that the 1st part in about making a model of the hrf with variation in shape (time and amplitude) then you would try to regress out something like the amplitude or so ?? I'm really unsure about all this ... sorry cyril -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.