In information-integration categorization, accuracy is maximized only if information from two or more stimulus components is integrated at some pre-decisional stage. In many cases the optimal strategy is difficult or impossible to describe verbally. Evidence suggests that success in information-integration tasks depends on procedural learning that is mediated largely within the striatum. Although many studies have examined initial information-integration learning, little is known about how automaticity develops in information-integration tasks. To address this issue, each of ten human participants received feedback training on the same information-integration categories for more than 11,000 trials spread over 20 different training sessions. Sessions 2, 4, 10, and 20 were performed inside an MRI scanner. The following results stood out. 1) Automaticity developed between sessions 10 and 20. 2) Pre-automatic performance depended on the putamen, but not on the body and tail of the caudate nucleus. 3) Automatic performance depended only on cortical regions, particularly the supplementary and pre-supplementary motor areas. 4) Feedback processing was mainly associated with deactivations in motor and premotor regions of cortex, and in the ventral lateral prefrontal cortex. 5) The overall effects of practice were consistent with the existing literature on the development of automaticity.