I would say you are quite right. At short TR e.g. (aliased) cardiac induced noise is no longer broad band and need to be modeled with a model which can capture oscillations in order to ensure that the residuals are i.i.d. This is not possible with an AR(1) model but could be done with RETROICOR see. Lund et al. 2006.
Best
Torben
Lund, T. E., Madsen, K. H., Sidaros, K., Luo, W.-L., & Nichols, T. E. (2006). Non-white noise in fMRI: Does modelling have an impact? NeuroImage, 29(1), 54–66. doi:10.1016/j.neuroimage.2005.07.005
Den Uge:19 13/05/2012 kl. 23.10 skrev Jeff Browndyke:
I thought it might have implications for both resting and task-based data given the possibility that the AR(1) noise correction isn't capturing everything sufficiently enough to have a truly random baseline. But, I could be wrong...