When you say "the length of the stimuli is user defined", do you mean that the stimulus length for each condition is equal to response time?
Have you tried looking at correct vs. incorrect responses for each condition as well?
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From: SPM (Statistical Parametric Mapping) [[log in to unmask]] on behalf of Efrat Sasson [[log in to unmask]]
Sent: Thursday, June 21, 2012 8:23 AM
To: [log in to unmask]
Subject: [SPM] strange fMRI results in methamatical task
I have conditions that are easier and conditions that are more difficult.
When I compare between easier and harder conditions, the easier conditions have much more activated brain regions compared to the harder conditions.
The task is mathematical. The region of activation are interesting regions and related to the task - parietal, frontal, cingulate.
I perform analysis using SPM 8 and it is event related, the length of the stimuli is user defined.
For contrast I use 1 and -1 when I am comparing two (or more) conditions.
Generaly there are 9 conditions. The everage RT for the easiest condition is 2007ms; the everage RT for the hardest condition is 3617.
We had no choice but to use different difficulty since it is "build in" in the task.
Where am I wrong? What could be an explansation for more activated regions in easier conditions?
This is a pilot of 5 subject and we are thinking what to change in the experiment itself.
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