Hi,
Lets say in one experiment, I give single stimulus pulses and want to model the response function for ~15s after each pulse, this is no problem with around 6-8 parameters for the TENT or SPLIN function.

But for a block design of 20s stimulus duration and expecting a fairly long BOLD response after stimulus offset (under- or overshoot..) I would need a huge amount of parameters, and since block design scans have also fewer repetitions than the event-related ones this may lead to problems with degrees of freedom.
(on a side note, is there an option for unequal spacing of the intervals, i.e. to have more beta weights for the interesting first 20s than for the post-stimulus response?)

How can I then compare the outputs (-iresp) of these two experiments and make statements about nonlinearities in scaling etc if they are so unequally spaced/computed?

Lastly, I would like to use the -iresp outputs of the event-related experiment as HRF model for the blocked designs (to convolve with the input function instead of the built-in GAM or SPM models). Since, however, I don't expect the shape of the individual responses to remain constant during repeated stimuli, I would like to use 3dNLfim to add some additional parameters - does this sound like a reasonable approach to you? I am willing to invest any time/effort necessary to adjust and experiment with the code for this attempt. It would also be a help if the actual formula of the modeled hemodynamic response can be extracted, rather than this interpolated data points that -iresp provides, is this possible in 3ddeconvolve?

If you have just any remark to any of these questions, I would very much appreciate it.
Thanks.



Edited 2 time(s). Last edit at 08/05/2013 10:23AM by paranoidandroid.