[pymvpa] modifying time_attr and onset when running fit_event_hrf_model with a dataset truncated at the beginning
benjsmith at gmail.com
Fri Jan 25 20:13:42 GMT 2019
I have a dataset with TR=2 where I want to delete the first 10 TRs (first
20 seconds) before running fit_event_hrf_model.
Deleting the first TRs is easy:
ds = ds[10:]
However I am unsure what to do with time coordinates. I understand that if
I adjust the onsets in the event list then I will also need to adjust the
time_attr in the dataset, like:
for e in event_list:
e['onset'] = e['onset']-10*TR
ds = ds.sa.time_coords - 10 * TR
result= fit_event_hrf_model(ds, event_list, time_attr='time_coords',
My intuition is that it shouldn't matter whether you adjust event onset and
ds time coordinates as long as you adjust both or neither - so that they
stay correctly aligned.
But when I run this and test, then I do get slightly different estimates
depending solely on whether I adjust the both time coordinates and event
onsets, or neither (keeping constant the removal of 10 trs).
Mainly I am wanting to know whether or not I should adjust the time
coordinates, but I would be interested to hear from anyone who knows why
estimates actually differ.
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