 |
 |
Again, thank you for your response. One last question, given a convolved HRF duration of 25s (stimulus duration 18s), and a TR of 2s, would it be more ideal to specify a window length of 24s with 12 bins or 26s with 13 bins? Or perhaps, in this situation, is it not best to have a number of bins corresponding to window length/TR? Thanks, Drew On 5/13/14 10:54 AM, "Helmut Nebl" <[log in to unmask]> wrote: >Well, actually you just have take the block length and add about 30 s, >this would be a reasonable window length then. Assume the canonical HRF >and a brief stimulus, then it takes about 30 s till baseline has reached >again. The same holds for longer durations. > >If you want to check and look at the expected time course, specify a >model with the canonical HRF as basis funtion, click on "Review", select >the SPM.mat, go on Design in the lower left window, then Explore, Session >1, select the condition of interest. The upper left plot shows you the >expected overall time course for that particular condition (note, this >ALWAYS corresponds to the unfiltered time course, so no high-pass filter >applied). If trials are relatively close together, it might be difficult >to detect when the expected time course reaches baseline again though. >Then simply set up an arbitrary model with a single event/block and the >corresponding block length. >