DescriptionDual system hypothesis suggests that there are two distinct memory systems, the instrumental system and the habit system. Our experiment is trying to demonstrate whether the dual system hypothesis is correct and under what circumstance we use each system. We used a same-different matching task. An observer had to respond rapidly whether a test consonant had just appeared in the study string by pressing one of two response keys, labeled same and different. When the same response was assigned to the right response key, there was no effect of study-string position on target RT, indicating that test item was not compared with the study string. When the different response was assigned to the right response key, same RT was an increasing function of the left-to-right position of a target in the study string and different RT was slower than same RT, indicating that during test the study string was serially generated and compared with the test item. fMRI confirmed that caudate and CA1 of hippocampus (habit system) were active when different was assigned to the right location and CA3 of hippocampus (instrumental system) was active when different was assigned to the left location.