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Abstract:
This study compared jittered versus constant stimulus
presentation rate in a rapid mixed trial fMRI experiment. Subjects
were instructed to respond to any Pokemon character except
"Meowth". A 75% target frequency was maintained across the study.
In the jittered condition, the interstimulus interval varied from 3
to 5 seconds and averaged 4 seconds while the other condition held
the stimulus presentation rate constant at 4 seconds. The T2* echo
planar images were acquired every two seconds (i.e., on average 2
scans per trial). MR signal increased in left motor cortex and
decreased in right middle and inferior frontal cortex for the
comparison of go versus nogo trials. The most robust changes were
observed for the constant stimulus presentation condition as
evidenced most obviously in the motor cortex. For left motor cortex
the maximum F ratio was 15.26 and number of voxels meeting the
statitical threshlold of .005 with contiguity threshold of 3 voxels
was 7 for the contant stimulus presentation rate and 6.89 and 3
voxels for the jittered condition. The results are discussed in
terms of post processing and analysis and the relevance of
preceding context on experimental design.
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