Re: [Marsbar-users] fitted event responses

[dsridhar <sri...@gm...>]

Sorry for the confusion. Here are some clarifications: 
a) The events are highly non-overlapping (separated by ~60s), so I don't
think that is a problem
b) Again, I am fitting the response with a Fourier model (6 basis
functions). So this makes no apriori assumptions about the shape of the HRF.

I think the problem is that I am using the 'Scaling' option (global
normalization), which creates a different fitted time-course compared to the
raw-event averaged BOLD response. I was wondering where I could find the
"scaled" time-course in the marsbar design object, D.

Also, I was wondering if the ROI time-series that MarsBar uses to fit the
model would be accessible from anywhere within the marsBar design object D
(this is the time-course that should be available inside D to create the fit
when the event_fitted function is called). That way I could just sweep all
adjustments SPM makes to the raw timecourse under the rug!

Many thanks,
Sridhar


Matthew Brett wrote:
> 
> Hi,
> 
>> This works great. However, when I extract raw time-courses with MarsBar
>> and
>> average the raw response across events and subjects, the raw and fitted
>> waveforms seem to differ by quite a bit.
> 
> Sorry, I am not quite sure what you mean.  If the events overlap, then
> the SPM model will attempt to estimate the effect of this overlap and
> adjust for it, in which case you'd expect some difference between the
> fitted events and the raw averaging.  Also, if you model for the event
> (such as HRF) is different from the actual response, SPM can't pick
> this up and the averaging and fitted responses will look different.
> 
> Is that what you meant?
> 
> Matthew
> 
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