In 3 experiments, participants memorized 8 examples, each exemplifying a different rule. Participants were asked to extend these rules to new examples. They practiced applications of the rules to examples over a period of 4 days (Experiment 1) or 5 days (Experiments 2 and 3). Although these rules were bidirectional, an asymmetry gradually built up such that participants became more facile in using the rules in the practiced direction. Participants also showed an advantage when the initial study example was repeated or when test examples were repeated. It is argued that skill acquisition involves development of a complex set of strategies based on use of rules and retrieval of examples. Four overlapping stages of skill acquisition are described.

The methodologies of cognitive architectures and functional magnetic resonance imaging can mutually inform each other. For example, four modules of the ACT-R (adaptive control of thought - rational) cognitive architecture have been associated with four brain regions that are active in complex tasks. Activity in a lateral inferior prefrontal region reflects retrieval of information in a declarative module; activity in a posterior parietal region reflects changes to problem representations in an imaginal module; activity in the anterior cingulate cortex reflects the updates of control information in a goal module; and activity in the caudate nucleus reflects execution of productions in a procedural module. Differential patterns of activation in such central regions can reveal the time course of different components of complex cognition.

To investigate the neural mechanisms of planning, we used a novel adaptation of the Tower of Hanoi (TOH) task and event-related functional MRI. Participants were trained in applying a specific strategy to an isomorph of the five-disk TOH task. After training, participants solved novel problems during event-related functional MRI. A computational cognitive model of the task was used to generate a reference time series representing the expected blood oxygen level-dependent response in brain areas involved in the manipulation and planning of goals. This time series was used as one term within a general linear modeling framework to identify brain areas in which the time course of activity varied as a function of goal-processing events. Two distinct time courses of activation were identified, one in which activation varied parametrically with goal-processing operations, and the other in which activation became pronounced only during goal-processing intensive trials.Regions showing the parametric relationship comprised a frontoparietal system and include right dorsolateral prefrontal cortex [Brodmann's area (BA 9)], bilateral parietal (BA 40͞7), and bilateral premotor (BA 6) areas. Regions preferentially engaged only during goal-intensive processing include left inferior frontal gyrus (BA 44). The implications of these results for the current model, as well as for our understanding of the neural mechanisms of planning and functional specialization of the prefrontal cortex, are discussed. P lanning is ubiquitous in our daily lives: we plan our workday, our child's birthday party, the most efficient route through the grocery store, and the organization of a manuscript such as this one. At a finer time scale, planning occurs when we solve multicolumn addition problems or puzzles such as the Tower of London (TOL) or Tower of Hanoi (TOH). It is at this time scale that we investigate the neural circuitry involved in the planning process.Since its introduction as a task to study planning from the information-processing perspective by Simon in 1975 (1), the TOH has been a prototype task in the study of high-level cognition and problem-solving behavior (2-4). TOH and TOL have been widely used in studies of patient populations as well (5-6), whereas recent neuroimaging studies have used TOL to map planning behavior onto brain activity (7-9).Recent research has investigated the role of brain areas such as the prefrontal cortex in the service of planning. However, Goel and Grafman (10) have suggested that, whereas patient populations (5, 6) and frontal patients (11,12) show deficits in performing planning tasks, a more precise analysis in terms of information-processing mechanisms is necessary to map functionality onto explicit cognitive mechanisms. By analyzing strategy use of their patient data in terms of formally specified information-processing models as described by Simon (1), these investigators identified the focal points of difficulty in TOH in frontal patients as deficiencies in short-term memory as well as difficulties...

Three experiments were run in which Ss first memorized examples of input-output pairs and then generated the outputs for a series of new inputs by analogy to the original examples. Ss first performed these mappings by explicit analogy to an example, but with practice they learned to make these input-output mappings directly without reference to the examples. Ss sped up as a power function of practice over a day (Experiment 1) or days (Experiments 2 and 3). Ss developed a directional asymmetry such that they were slower to calculate the input from the output than the output from the input (whereas initially they had not been). Ss showed similar speed up in their ability to recall the original examples but did not show the same directional asymmetry. Initially, there was some transfer from practicing the procedure to recalling the examples, but this diminished over days.