this article are also gratefully acknowledged

When subjects switch between a pair of stimulus–response tasks, reaction time is slower on trial N if a different task was performed on trial N � 1. We present a parallel distributed processing (PDP) model that simulates this effect when subjects switch between word reading and color naming in response to Stroop stimuli. Reaction time on ‘‘switch trials’ ’ can be slowed by an extended response selection process which results from (a) persisting, inappropriate states of activation and inhibition of task-controlling representations; and (b) associative learning, which allows stimuli to evoke tasks sets with which they have recently been associated (as proposed by Allport & Wylie, 2000). The model provides a good fit to a large body of empirical data, including findings which have been seen as problematic for this explanation of switch costs, and shows similar behavior when the parameters are set to random values, supporting Allport and Wylie’s proposal. © 2001 Elsevier Science Key Words: task switching; task set; Stroop effect; parallel distributed processing; executive functions. Atkinson and Shiffrin (1968) proposed a distinction between relatively permanent cognitive structures, such as short- and long-term memory, and control processes which harness those fixed structures in order to attain specific goals. This distinction was elaborated in the following years (e.g.,

WhH subjectsswitch between two tasks, performance is slower after a taskswitch tht after a task repetition. We report five experimentsshperi thp a large part ofth)I "task-sh5S) costs" cannot be attributed to a control operation, needed to configureth cognitive system for th upcoming task (e.g., Rogers & Monsell, 1995). In all experiments subjects switchs between picture-naming and word-reading. We presented di#erent stimulieithl in just one of th two tasks, or inboth ofth9S ShSI#qH(93 were larger for stimuli presented inboth tasks ths forthH3 presented in only one task, even after more the 100 intervening trials between prime and probe events. We suggest (as proposed by Allport & Wylie, 2000)th0 stimuli acquire associationswith th tasks inwh9E th9 occur.Whu th current task activation is weak, as on aswitch of tasks, stimuli can trigger retrieval of th associated, competing task, provoking larger time costs.

"If, in voluntary action properly so-called, the act must be foreseen, it follows that no creature not endowed with divinatory power can perform an act voluntarily for the first time". There is quite a bit of information that William James (1890, p. 487) wanted to communicate to the reader with this sentence. First, he incidentally introduces the probably most common

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,...

ABSTRACT—This study examined the role of verbal labeling in 4-year-old children’s acquisition of action-effect learning. The acquisition of action-effect associations was tested by having children first perform a two-choice key-pressing task in which each key press was followed by an effect (i.e., a particular sound) and then respond to the previously perceived effects under either consistent or inconsistent key-sound mappings. During acquisition, the children overtly described the actions, the effects, both the actions and the effects, or, in a control condition, something irrelevant to the actions and effects. Action-effect learning was reliable only if the description related actions to effects, even though some evidence of learning was also obtained in the control condition. In contrast, learning was prevented if only the actions or only the effects were described. The results suggest that verbal labeling plays an important role in integrating and isolating event representations. Vygotsky (1934/1962) was probably one of the first to assume a central role of language in the emergence of voluntary action in humans. In particular, he claimed that the dynamic interplay between language and action regulation undergoes a transition in early development: In the young child, action comes first. Imagine a child painting something. He or she is likely to first finish the picture and then say what he or she has painted. In the next phase, action and speech go together, so that the child will talk while painting an object. In the final stage, speech commonly precedes action: The older child will say what he or she intends to paint before actually starting to paint. Apparently, by this point, speech has taken on a self-regulatory function in specifying the action goal. Considering this example, one can envision at least two functions of language in the development of action control. First, Address correspondence to Jutta Kray, Department of Psychology,

this article. We also thank Phil Allen, Jim Johnston, Joel Lachter, and Roger Remington for their insight and valuable discussions

The authors argue that human sequential learning is often but not always characterized by a shift from stimulus- to plan-based action control. To diagnose this shift, they manipulated the frequency of 1st-order transitions in a repeated manual left–right sequence, assuming that performance is sensitive to frequencyinduced biases under stimulus- but not plan-based control. Indeed, frequency biases tended to disappear with practice, but only for explicit learners. This tendency was facilitated by visual–verbal target stimuli, response-contingent sounds, and intentional instructions and hampered by auditory (but not visual) noise. Findings are interpreted within an event-coding model of action control, which holds that plans for sequences of discrete actions are coded phonetically, integrating order and relative timing. The model distinguishes between plan acquisition, linked to explicit knowledge, and plan execution, linked to the action control mode.

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this article without authors' permission) The Absence of A Switch Cost When Preparing for Multiple Tasks: Interactions Between Element- and Ensemble-Level Effects Mei-Ching Lien & Eric Ruthruff NASA Ames Research Center Six experiments examined an intriguing result from a dual-task study by De Jong (1995) where no task-switch cost was found. We investigated whether this phenomenon is due to the formation of task ensembles - a control structure covering more than one task element (e.g., prepare Task 1 and the switch to Task 2). Experiment 1, where tasks were performed individually, showed the usual large switch cost (182 ms). This cost disappeared and even reversed in Experiments 2-5, where the temporal and/or spatial contiguity between adjacent task elements was increased to encourage ensemble formation. In Experiment 6, the switch cost between elements was large within an ensemble, but small or nonexistent between ensembles. These data suggest that the element-level effect is fragile and can be reduced or eliminated when a higher-level control structure is formed. A dual-route model of task switching is proposed