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
>
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>
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--
Shahin Nasr
PhD in Cognitive Neuroscience
Martinos Imaging Center, MGH
Harvard Medical School
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