Dear SPM experts,
I have questions about 'contrasts' in SPM99b.
Question 1,
I acquired a blocked-designed fMRI dataset which comprises three task
conditions, A, B and C, repeated in this order in a session. The dataset
has no rest or control conditions. I would like to know the brain regions
which are responsible for each of the three tasks (that is, regions for
A, regions for B and regions for C). I suppose one of the following
procedures would do for this purpose.
(1) In the 'fMRI models' specification, 'number of conditions or trials'
should be specified as "3". In the 'Select contrasts...' section of the
'Results' specification, contrasts should be defined as "1 0 0" for task
A, "0 1 0" for task B and "0 0 1" for task C.
(2) Statistics should be performed separately for each of the three
tasks. In the 'fMRI models' specification, 'number of conditions or
trials' should be specified as "1" for a task and the other conditions
should not be mentioned. In the 'Select contrasts...' section of the
'Results' specification, a contrast should be defined as "1". This
procedure would be repeated for three times, for task A, B and C.
Which, or the other, procedure is appropriate ?
Question 2,
When analyzing fMRI datasets which comprise multiple task conditions (A,
B, C for example) and a control (rest) condition (R), which of the below,
or the other, procedures is followed in SPM99b ?
(1) In SPM99b, the control (rest) condition is unspecified by users.
Instead, 'SOA' and 'epoch length' for the control are calculated by those
inputted for tasks. Thus, contrasts such as 'A - R', 'B - R' and 'C - R'
can be defined in addition to 'A - B', 'B - C' and so on.
(2) When analyzing for task A, the other tasks (B, C) and rest (R) are
handled together as 'control', compared with task A. Thus, activation
maps are generated by contrasts such as 'A - BCR', 'B - ACR' or 'C - ABR'.
Thank you in advance,
Kayako Matsuo
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Kayako MATSUO [log in to unmask]
Life Electronics Research Center
Electrotechnical Laboratories,
1497-1 Teragu, Tsukuba, 300-4201 Japan
tel) +81-298-69-1916
fax) +81-298-69-2152
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