Thanks Doug. In my experiment, each trial (event) consists of 1 sec stimulus presentation and 5 sec blank interval (TR=2). I have also added a condition with just blank presentation which will be repeated as much as other events.
I have used optseq2 commands to generate the trial sequence. But I faced two problem/questions: 1) Using this command, I expected to see a Null event (other than my blank condition) with variable length (irrespective of TR) between other trials. But to my surprise, length of the Null event was always a multiplication of TR. Is that correct? 2) Also, for "psdmin psdmax" I wasn't sure if they are number of TRs or number of seconds and what is a safe window length when my stimuli are very simple visual objects (and no cognitive task). Once again, thanks for your help. On Fri, Dec 9, 2011 at 1:10 PM, Douglas N Greve <gr...@nmr.mgh.harvard.edu>wrote: > Hi Shahin, there are several ways to answer this question. If you are > going to analyze assuming a shape to the HRF, then the actual delay between > stimuli is technically not important (though 4s will be good to avoid > attenuation in the following stimulus). If you're using an FIR model of the > HRF (no assumed shape), then I usually advise that you have, in total, as > much time spent on fixation (or whatever your null stimulus is) as you have > for any other stimulus. You can use optseq to compute the actual schedule. > doug > > > SHAHIN NASR wrote: > >> Hi Surfers, >> >> It is my first experience with Event-related paradigms. In my >> experiment, trials take minimum 6s (TR=2s). I wonder what is the optimum >> variable delay between trials to be able to analyze data without any >> confound. >> >> Regards >> >> -- >> Shahin Nasr >> >> PhD in Cognitive Neuroscience >> Martinos Imaging Center, MGH >> Harvard Medical School >> >> > -- > Douglas N. Greve, Ph.D. > MGH-NMR Center > gr...@nmr.mgh.harvard.edu > Phone Number: 617-724-2358 Fax: 617-726-7422 > > Bugs: > surfer.nmr.mgh.harvard.edu/**fswiki/BugReporting<http://surfer.nmr.mgh.harvard.edu/fswiki/BugReporting> > FileDrop: > www.nmr.mgh.harvard.edu/**facility/filedrop/index.html<http://www.nmr.mgh.harvard.edu/facility/filedrop/index.html> > > > > 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<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. > > -- Shahin Nasr PhD in Cognitive Neuroscience Martinos Imaging Center, MGH Harvard Medical School
_______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu 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.