First of all, the number of stimuli should not influence the estimate of the % change, only its variance (ie, it won't bias you to find a change that is not there). Having said that, you can get some non-linearities if stimuli are too close to each other, so you'll want to make sure to check that the average interstimulus time is about the same. I don't have a strong feeling about whether VRF or efficiency is better -- I don't think I would stress to much over the difference.
doug [email protected] wrote: > Hi Doug and other Freesurfers, > > We are trying to balance the power of different event-related fMRI runs > (each consisting of a different experimental condition with different > interstimulus intervals) using the optseq2 definition for efficiency. Our > outcome metric is the BOLD % signal change amplitude - we expect different > runs to show different amplitudes. We use a FIR model. Because of the > variable under investigation (interstimulus interval) we must have > different number of stimuli in each run. > > We are uncertain as to which optseq2 efficiency measure more accurately > suits this situation. I know you typically prefer "VRF" over "Efficiency". > However, is VRF better suited for reflecting the power of statistical > contrast (for example for t-test and F-values) as opposed to "raw" BOLD % > signal change? In other words, would "Efficiency" more accurately reflect > the balance for just the BOLD % signal change? > > The ultimate goal is to make sure that changes in BOLD % signal change > amplitude are not due to the different number of stimuli across runs. > > Thanks! > > Best regards, > > Tommi > > --- > Tommi Raij, M.D., Ph.D. > MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging > Bldg 149, 13th St > Charlestown, MA 02129 > U.S.A. > _______________________________________________ > Freesurfer mailing list > [email protected] > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > > > -- Douglas N. Greve, Ph.D. MGH-NMR Center [email protected] Phone Number: 617-724-2358 Fax: 617-726-7422 Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting FileDrop: www.nmr.mgh.harvard.edu/facility/filedrop/index.html _______________________________________________ Freesurfer mailing list [email protected] https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
