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A new theoretical framework, the EPIC (Executive-Process/Interactive-Control) architecture, provides the basis for accurate detailed computational models of human multipletask performance. Contrary to the traditional response-selection bottleneck hypothesis, EPIC's cognitive processor can select responses and do other procedural operations simultaneously for multiple concurrent tasks. Using this capacity together with flexible executive control of peripheral perceptual-motor components, EPIC computational models account well for various patterns of mean reaction times,. systematic individual differences in multiple-task performance, and influences of special training on people's task-coordination strategies. These diverse phenomena, and EPIC's success at modeling them, raise strong doubts about the existence of a pervasive immutable response-selection bottleneck in the human information-processing system. The present research therefore helps further characterize the nature of discrete versus continuous information processing.

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Humans perform actions to reach particular goals, that is, to intentionally create or modify personally relevant events---we move our eyes to learn more about a novel event, reach for a cup to quench our thirst, and move our lips to share our thoughts with someone else. Accordingly, even primitive actions must involve some kind of planning, some sort of anticipatory control. Indeed, there are at least three defining features that the simplest behavioral acts share with more complex ones. First, all of them are planned in terms of anticipated goal events. In particular, the first step of action planning consists in specifying the features the action is intended to possess; this is achieved by activating the appropriate action-effect codes, i.e., sensory-motor assemblies controlling the production of those features. Action-effect codes emerge through the perception of movement-effect contingencies, and they are acquired from the first months in life on. Besides action planning they are involved in the perception of both one's own actions and actions of others. Second, selected features of an intended action need to be integrated into a coherent, durable action plan, which is achieved by temporarily "binding" distributed feature codes. Third, planning an action turns the cognitive system into a kind of reflex machinery, which facilitates the proper execution of the plan under appropriate circumstances. This involves the implementation of automatic stimulus-response associations and the increase of the salience of action-related situational information, thereby delegating action control to the environment.

This paper reviews recent approaches to human action planning and the cognitive representation of intentional actions. Evidence suggests that action planning takes place in terms of anticipated features of the intended goal, that is, in terms of action effects. These effects are acquired from early infancy on by registering contingencies between movements and perceptual movement outcomes. Co-occurrence of movements and effects leads to the creation of bidirectional associations between the underlying internal codes, thus establishing distributed perception-action networks subserving both perceiving external events and intentionally producing them. Action plans determine only the general, goal-relevant features of intended actions, while the fine-tuning is left to on-line sensory-motor processing. Action plans emerge from competition for action control between several factors: overlearned habits, perceptual events, and emotional influences, among others. Accordingly, action control represents a balance between personal intentions and wishes on the one hand and environmental affordances and demands on the other. KEYWORDS: action planning, intentional action, goal, perception and action, feedback, action effects, action control, will, priming, imitation, mirror neurons, emotion and action DOMAINS: behavioral psychology, cognition, development, learning and memory, motor processes, sensation and perception, neuroscience, behavior PLANNING AN ACTION Humans perform actions to reach goals, that is, to create or modify some event or state of affairs according to their intentions --- otherwise we would talk of movement but not action. Logically, then, intentional, goal-directed action presupposes some sort of (conscious or unconscious) anticipation of the intended goal event,...

The article describes the general methods and some of the results obtained in the

this article should be addressed to E. Ruthruff, Department of Psychology, University of California--San Diego, La Jolla, CA 92093-0109, or to J. Miller, Department of Psychology, University of Otago, P.O. Box 56, Dunedin, New Zealand

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