From: Marek Meier <marekmeier@gm...>  20130711 09:46:29

<html><head></head><body><div style="fontfamily: Verdana;fontsize: 12.0px;"><div> <div>Dear MarsBar experts,</div> <div> </div> <div>I hope that someone will find the time to help me with my questions. I used an HRF function in my model and I have two different conditions (each 4 s) and the mean duration of my jittered ISI is 5 s. I want to extract times course and I'm not sure whether I have to use the fitted event time course or FIR event time course.</div> <div> </div> <div>1. Can I use the FIR event time course function or would that be wrong given that I used an HRF function in my model?</div> <div> </div> <div>2. What is the meaning of the numerical values in the "time_course" variable if I use "fitted event time course"? With an event duration of 4 s I get 191 values. How can I use these values to calculate the time course for a certain time, e.g. 12 seconds?</div> <div> </div> <div>Any help is greatly appreciated.</div> <div> </div> <div>Best wishes</div> <div>Marek</div> <div> </div> <div> </div> </div></div></body></html> 
From: Matthew Brett <matthew.brett@gm...>  20130803 00:22:22

Hi, Sorry to be slow to reply. On Thu, Jul 11, 2013 at 2:46 AM, Marek Meier <marekmeier@...> wrote: > Dear MarsBar experts, > > I hope that someone will find the time to help me with my questions. I used > an HRF function in my model and I have two different conditions (each 4 s) > and the mean duration of my jittered ISI is 5 s. I want to extract times > course and I'm not sure whether I have to use the fitted event time course > or FIR event time course. > > 1. Can I use the FIR event time course function or would that be wrong given > that I used an HRF function in my model? It would not be wrong, but I recommend you use the FIR model, and then use the fitted time course in Marsbar. The FIR event time course fits a new FIR model just to the event of interest (not the other events, which continue to have HRF models). That makes it a little hard to think about what might have happened because one event has a richer model than the others. That's way I personally prefer FIR modeling in the first place. > 2. What is the meaning of the numerical values in the "time_course" variable > if I use "fitted event time course"? With an event duration of 4 s I get 191 > values. How can I use these values to calculate the time course for a > certain time, e.g. 12 seconds? You mean why are there 191 values? SPM, when it generates its model, uses what it calls a 'supersampled' time series to generate the regressors, which are then downsampled to the TR. The supersampled series has time deltas of TR / 16. The standard length in time for the event basis functions is 34ish seconds. So, say your TR was around 2.5, then the time course would have; dt = 2.5 / 16; 34 / dt = 217 time points. What do you mean by 'time course for a certain time? Sorry if I'm missing something, Best, Matthew 