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If you are simply doing a task design and your ITI is over 1second, then you can use 0 seconds as the duration. Specifying the wrong duration for neural activity less than 2 seconds has little impact on the shape of the response you are trying to detect (for more detail, see http://imaging.mrc-cbu.cam.ac.uk/imaging/DesignEfficiency) If you are doing DCM or PPI or gPPI analyses, the duration will have a much larger impact. If there is any literature on a more direct measure of pain activity, I would try to use that to estimate the length of the neural activity. In my experience, modeling something one way because previous studies have modeled it that way may or may not be a good choice. You need to have a theoretical reason for making your decisions with respect to creating your model including the duration of events. Best Regards, Donald McLaren ================= D.G. McLaren, Ph.D. Research Fellow, Department of Neurology, Massachusetts General Hospital and Harvard Medical School Postdoctoral Research Fellow, GRECC, Bedford VA Website: http://www.martinos.org/~mclaren Office: (773) 406-2464 ===================== This e-mail contains CONFIDENTIAL INFORMATION which may contain PROTECTED HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED and which is intended only for the use of the individual or entity named above. If the reader of the e-mail is not the intended recipient or the employee or agent responsible for delivering it to the intended recipient, you are hereby notified that you are in possession of confidential and privileged information. Any unauthorized use, disclosure, copying or the taking of any action in reliance on the contents of this information is strictly prohibited and may be unlawful. If you have received this e-mail unintentionally, please immediately notify the sender via telephone at (773) 406-2464 or email. On Thu, May 7, 2015 at 9:59 AM, Mark <[log in to unmask]> wrote: > Dear Donald, > > Thanks for your clarification. It makes sense. However, I still don't know > the duration I should input in the GLM..... > > In pain study, hemodynamic responses return to the baseline about several > seconds after the cessation of a painful stimulation. Usually, if pain > stimulus duration lasts for seconds (e.g. 5-second heat pain), people used > to specify 5 seconds as the duration in the GLM, rather than, for example, > 10 seconds. > > Mark > > > >