Dear SPMers,
I would like to know if my modification of hrf is suitable for our event
fMRI study analysis.
We did an event related study about sentence comprehension. Our concern is
the relation between the word order in a sentence and cerebral activation.
Event length was 30 seconds and TR=1.
There were two conditions (two types sentences), A and B, in a random order,
12 events for each (then 24 x 30s). The total scan time was 720 second and
the total scan was 720 (actually the total number of the scans was 725 and
the first 5 scan was not used).
The stimuli sentences were consist of 3 words (e.g., John kissed Mary)
presented word by word. Each event was 30s and the first 10s was rest. At
11s, 12s and 13s, the first, the second and the third word was presented.
Then, to test the subjects surely read the stimuli, a question sentence was
presented at 15s and the subjects responded by button press (the response
occured around17-18s). The rest of the event (from 18-19s to 30s) was also
rest (a small fixation was presented).
We would like to see the activation againt the first word. (type A sentence
is more difficult than type B to understand because of its word order)
All our concern is the cerebral activation occured 11, 12, 13s.
Then I changed spf_hrf
delay of undershoot 16 -> 7
length of kernel 32 -> 12
At fMRI models and estimation, I selected all 720 scans.
condition =2
SOA = variable
I set the vector onset for the two conditions as
for condition 1: 11, 101, 131..., 701
for condition 2: 41, 71, 161, ..., 671
Those are the onset time of the first words presentation (at 11s).
For 12s, vector onset was set as, 12, 102, 132, ..., 702,
and For 13s, it was set as, 13, 103, 133, ..., 703 for condition1 and did
the same way for condition 2.
The result seems reasonable. But I am not sure if this process is corect or
not.
Is this way of analyzing is wrong? Or are there any better ways?
I thank everybody for helpful advises.
Shigeki Tanaka, M.D.
Department of Cognitive Neuroscience
Okatani Hospital, Nara, Japan
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