On Tue, Mar 08, 2011 at 12:12:01PM -0500, Yaroslav Halchenko wrote: > and first initial rest block in each chunk having 6 volumes (I think). So, if > we forget for a moment that we got 121 volumes instead of 120, then initial > rest block should have indeed been allocated 5 volumes (although once again > not exactly, due to 12/2.5 = 4.8) instead of 6 volumes. Thus you could > probably consider indeed that all labels in the dataset are shifted by 2 > volumes, and I should have not added 1 volume on both sides of a stimuli > block, > but rather 2 on the front, if I was looking for "precise" timing in terms of > volumes. But then you would obtain 7 rest volumes at the end of each run > (121st volume?) That would be my speculation atm
To add another tiny bit of evidence for a shift you could take a look at the peristimulus plot at http://www.pymvpa.org/tutorial_eventrelated.html The block onset as encoded in the label vector is the t=2 volume/timepoint in the plot. You'll see that this volume already reflects a deviation from baseline for both plotted conditions. Therefore, I'd say that, on average, the labels are shifted by one volume -- considering all temporal uncertainty introduced by the timing of the study that Yarik mentioned before. Michael -- Michael Hanke http://mih.voxindeserto.de _______________________________________________ Pkg-ExpPsy-PyMVPA mailing list [email protected] http://lists.alioth.debian.org/mailman/listinfo/pkg-exppsy-pymvpa
