Setting it to 0 convolves the HRF with a delta function. Setting it to something longer convolves it with a boxcar. If your stimulus is 4-5 seconds, then you should put that down as the duration.
Chris
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From: SPM (Statistical Parametric Mapping) [[log in to unmask]] On Behalf Of Chaleece Sandberg [[log in to unmask]]
Sent: Tuesday, August 16, 2011 2:08 PM
To: [log in to unmask]
Subject: [SPM] event duration 0
In the model specification, what is considered an instantaneous event? What is setting the durations to 0 doing with the hemodynamic response curve- is it taking the whole potential curve into account or only the first instantaneous response and binning the time according to the dt, or something else?
For context, we are running an E-Prime experiment with a picture stimulus displayed for 4 or 5 seconds, followed by a fixation for 2 or 4 seconds, and we want to know what is the most effective way to model the response curve for viewing the picture stimulus.
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