Electrophysiological studies in monkeys and neuroimaging studies of humans have shown that action execution and action observation share neural processing sites traditionally thought to be responsible for motor execution alone. This experiment investigates a behavioral phenomenon in which a visual discrimination task is influenced by concurrent motor performance. Functional magnetic resonance imaging (fMRI) was used to determine whether this discrimination task uses components of the motor system. Participants viewed and responded to an animated hand while performing either congruent or incongruent right hand actions; the visual presentation was either a sequence showing a hand opening and closing, or randomly ordered frames from this series. The participant responded to onscreen target hand postures on a left footpedal. Previous behavioral results have shown a reaction time advantage on this discrimination task when performing congruent compared to incongruent hand actions, but only for sequential visual presentation. Left superior parietal lobule (SPL) and dorsal premotor cortex were more strongly activated when visual series and hand action did not match, as were dorsal premotor cortex and primary visual cortex. These results suggest that mismatches between performed action and visual feedback produce an inaccurate neural representation of limb state, which we suggest causes the contralateral SPL activation. This representation could not be used in the visual discrimination task, requiring increased reliance on direct visual inputs in order to perform the discrimination task accurately.