Dear Andrew, Hello. In a paper that I have out under review I used a similar model. I included a scatter plot of the statistical tolerances for each person for each regressor (stimulus, retention, cue) of interest. This was to show that even though this type of model has collinearities in it, the statistical tolerance was above the standard acceptable limit of 0.8 for all subjects. I do not have any aggregate for the effects of tolerance at the 2nd level though. So if you request it as a reviewer I do not see it as being too far out. SPSS provides it in their table of results. take care, Jason On Wed, Nov 9, 2011 at 3:58 PM, Andrew Mattarella-Micke <[log in to unmask]> wrote: > Note also that one must be extremely careful in specifying the predictors. There may be neural activity that varies with the duration of the intra-trial spacing (i.e., delay related activity). In this case, designs may suffer from multicollinearity, even with long null events. > > Here are some relevant papers that I've been looking at for my own benefit: > > Andrade, a, Paradis, a L., Rouquette, S., & Poline, J. B. (1999). Ambiguous results in functional neuroimaging data analysis due to covariate correlation. NeuroImage, 10(4), 483-6. doi:10.1006/nimg.1999.0479 > > Ollinger, J. M., Corbetta, M., & Shulman, G. L. (2001). Separating processes within a trial in event-related functional MRI. NeuroImage, 13(1), 218-29. doi:10.1006/nimg.2000.0711 > > Ruge, H., Brass, M., Lohmann, G., & von Cramon, D. Y. (2003). Event-related analysis for event types of fixed order and restricted spacing by temporal quantification of trial-averaged fMRI time courses. Journal of magnetic resonance imaging : JMRI, 18(5), 599-607. doi:10.1002/jmri.10397 > > Ruge, H., Goschke, T., & Braver, T. S. (2009). Separating event-related BOLD components within trials: the partial-trial design revisited. NeuroImage, 47(2), 501-13. Elsevier Inc. doi:10.1016/j.neuroimage.2009.04.075 > > Serences, J. T. (2004). A comparison of methods for characterizing the event-related BOLD timeseries in rapid fMRI. NeuroImage, 21, 1690 - 1700. doi:10.1016/j.neuroimage.2003.12.021 > > > In particular, Ruge et al. (2009) have a very rigorous treatment of partial trials. I wonder if it's even possible to reduce multicollinearity substantially through sub-12 sec jittering alone, perhaps through an optimal search of the design space (e.g., Wager & Nichols, 2003, or Kao et al., 2009). I haven't run any simulations, but my expectation is that it's probably not possible. > > > Andrew Mattarella-Micke >