FIR stands for "Finite Impulse Response". You define a time window that brackets your stimulus response then compute the average response at each time point inside the window. Eg, the window might start at stimulus onset (psd=0) and be sampled at each TR (eg, 2 sec) until the end of the window (eg, 26 sec). You can then plot the average at each time to see what the response looks like. See the Dale and Buckner paper (1998?) for more details. The FIR makes the fewest assumptions about the shape of the hemodynamic response (the opposite extreme is assuming a gamma function or difference of gammas).
It is almost impossible to analyze the separate components inside of a compound event unless you assume a shape to the function. I don't know what people do who want to have randomization inside a compound event. Probably just use their computers "rand" function. doug Asaf Kaftory wrote: > Hello list, > > attached is my first post plus my new questions underneath every > paragraph. thanks. > > > > > > > I'm new to optseq, and would like your help with the following issues: > > > 1. What exactly does DPSD mean? and why does the TR has to be an > > integer of it? > > > > Doug: Delta Post-Stimulus Delay. The time between samples in the > > FIR. Usually, it is just the TR. If you want to do sub-TR estimation, > > you can make it less than the TR. It has to be an integer divisor of > > the TR because it forms the basic "tick" of the clock. > > > Asaf: I'm afraid i didn't get the explanation. what is the FIR, and > what > > are the the samples in it ? > > > > 2. My experiment design uses jitter - both ITI (i.e., between > > > trials) and ISI (i.e., between stimulus within a compound event). As i > > > understood, optseq can only supply me with the ITI jitter but no the > > > ISI jitter. is that right? do you happen to know a computerized method > > > to introduce a jitter within a compound event? > > > > Doug: That is right. Sorry, don't know of anything that will give you > > with-in event jitter. > > Asaf: ok, thanks. isn't it strange though? how do researches > jitter the > > ISI than? manually? > > > > > 3. Is it true that jitter in optseq is made by inserting "NULLS", > > > and that the DPSD determines the "steps" of the jitter (for e.g., if > > > DPSD equals 1, Nullmin equals 2 and Nullmax equals 4, the NULL events > > > will be 2 3 or 4). Did i understand it right? > > > > Doug: Yes. > Asaf: thanks. > > hope all is clearer now, > Asaf. > > ------------------------------------------------------------------------ > *From:* Douglas N Greve <gr...@nmr.mgh.harvard.edu> > *To:* Asaf Kaftory <asaf_kaft...@yahoo.com> > *Cc:* freesurfer@nmr.mgh.harvard.edu > *Sent:* Tue, October 6, 2009 6:16:37 PM > *Subject:* Re: [Freesurfer] optseq2 help: DPSD and jitter > > I don't know what "two samples" refers to. > > doug > > Asaf Kaftory wrote: > > Hey Doug - first of all, thanks for the reply. second - > > > > 1. I'm afraid i didn't get the explanation. what is the FIR, and what > > does it mean "two samples in the FIR" ? > > > > 2. ok, thanks. isn't it strange though? how do researches jitter the > > ISI than? manually? > > > > 3. thanks. > > *From:* Doug Greve <gr...@nmr.mgh.harvard.edu > <mailto:gr...@nmr.mgh.harvard.edu>> > > *To:* Asaf Kaftory <asaf_kaft...@yahoo.com > <mailto:asaf_kaft...@yahoo.com>> > > *Cc:* freesurfer@nmr.mgh.harvard.edu > <mailto:freesurfer@nmr.mgh.harvard.edu> > > *Sent:* Saturday, September 26, 2009 7:42:43 PM > > *Subject:* Re: [Freesurfer] optseq2 help: DPSD and jitter > > > > > > On Sat, 26 Sep 2009, Asaf Kaftory wrote: > > > > > Hello list, > > > > > > I'm new to optseq, and would like your help with the following issues: > > > 1. What exactly does DPSD mean? and why does the TR has to be an > > integer of it? > > > > Delta Post-Stimulus Delay. The time between samples in the > > FIR. Usually, it is just the TR. If you want to do sub-TR estimation, > > you can make it less than the TR. It has to be an integer divisor of > > the TR because it forms the basic "tick" of the clock. > > > > > 2. My experiment design uses jitter - both ITI (i.e., between > > > trials) and ISI (i.e., between stimulus within a compound event). As i > > > understood, optseq can only supply me with the ITI jitter but no the > > > ISI jitter. is that right? do you happen to know a computerized method > > > to introduce a jitter within a compound event? > > > > That is right. Sorry, don't know of anything that will give you > > with-in event jitter. > > > > > 3. Is it true that jitter in optseq is made by inserting "NULLS", > > > and that the DPSD determines the "steps" of the jitter (for e.g., if > > > DPSD equals 1, Nullmin equals 2 and Nullmax equals 4, the NULL events > > > will be 2 3 or 4). Did i understand it right? > > > > Yes. > > > > doug > > > > > > > > hope to hear from you soon, > > > Asaf. > > > > > > > > > > > > > -- > > Douglas N. Greve, Ph.D. > > MGH-NMR Center > > gr...@nmr.mgh.harvard.edu <mailto:gr...@nmr.mgh.harvard.edu> > <mailto:gr...@nmr.mgh.harvard.edu <mailto:gr...@nmr.mgh.harvard.edu>> > > Phone Number: 617-724-2358 > > Fax: 617-726-7422 > > > > In order to help us help you, please follow the steps in: > > surfer.nmr.mgh.harvard.edu/fswiki/BugReporting > <http://surfer.nmr.mgh.harvard.edu/fswiki/BugReporting> > > <http://surfer.nmr.mgh.harvard.edu/fswiki/BugReporting> > > > > > > > > ------------------------------------------------------------------------ > > > > _______________________________________________ > > Freesurfer mailing list > > Freesurfer@nmr.mgh.harvard.edu <mailto:Freesurfer@nmr.mgh.harvard.edu> > > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > > -- > Douglas N. Greve, Ph.D. > MGH-NMR Center > gr...@nmr.mgh.harvard.edu <mailto:gr...@nmr.mgh.harvard.edu> > Phone Number: 617-724-2358 > Fax: 617-726-7422 > > In order to help us help you, please follow the steps in: > surfer.nmr.mgh.harvard.edu/fswiki/BugReporting > > > > ------------------------------------------------------------------------ > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer -- Douglas N. Greve, Ph.D. MGH-NMR Center gr...@nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422 In order to help us help you, please follow the steps in: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
