& The abrupt onset of a novel event captures attention away from, and disrupts, ongoing task performance. Less obvious is that intentional task switching compares with novelty-induced behavioral distraction. Here we explore the hypothesis that intentional task switching and attentional capture by a novel distracter both activate a common neural network involved in processing contextual novelty [Barcelo, F., Periáñez, J. A., & Knight, R. T. Think differently: A brain orienting response to task novelty. NeuroReport, 13, 1887–1892, 2002.]. Eventrelated potentials were recorded in two task-cueing paradigms while 16 subjects sorted cards following either two (color or shape; two-task condition) or three (color, shape, or number; three-task condition) rules of action. Each card was preceded by a familiar tone cueing the subject either to switch or to

& Using event-related potentials (ERPs), we investigated the neural response associated with preparing to switch from one task to another. We used a cued task-switching paradigm in which the interval between the cue and the imperative stim-ulus was varied. The difference between response time (RT) to trials on which the task switched and trials on which the task repeated (switch cost) decreased as the interval between cue and target (CTI) was increased, demonstrating that sub-jects used the CTI to prepare for the forthcoming task. How-ever, the RT on repeated-task trials in blocks during which the task could switch (mixed-task blocks) were never as short as RTs during single-task blocks (mixing cost). This replicates previous research. The ERPs in response to the cue were compared across three conditions: single-task trials, switch trials, and repeat trials. ERP topographic differences were found between single-task trials and mixed-task (switch and repeat) trials at 160 and 310 msec after the cue, indicative of changes in the underlying neural generator configuration as a basis for the mixing cost. In contrast, there were no topographic differences evident between switch and repeat trials during the CTI. Rather, the response of statistically in-distinguishable generator configurations was stronger at 310 msec on switch than on repeat trials. By separating dif-ferences in ERP topography from differences in response strength, these results suggest that a reappraisal of previous research is appropriate. &

Prior research has linked visual perception of tools with plausible motor strategies. Thus, observing a tool activates the putative action-stream, including the left posterior parietal cortex. Observing a hand functionally grasping a tool involves the inferior frontal cortex. However, tool-use movements are performed in a contextual and grasp specific manner, rather than relative isolation. Our prior behavioral data has demonstrated that the context of tool-use (by pairing the tool with different objects) and varying hand grasp postures of the tool can interact to modulate subjects ’ reaction times while evaluating tool-object content. Specifically, perceptual judgment was delayed in the evaluation of functional tool-object pairings (Correct context) when the tool was non-functionally (Manipulative) grasped. Here, we hypothesized that this behavioral interference seen with the Manipulative posture would be due to increased and extended left parietofrontal activity possibly underlying motor simulations when resolving action conflict due to this particular grasp at time scales relevant to the behavioral data. Further, we hypothesized that this neural effect will be restricted to the Correct tool-object context wherein action affordances are at a maximum.

The neural mechanisms of semantic and response conflicts: An fMRI study of practice-related effects in the Stroop task

■ Coordination between networks of brain regions is impor-tant for optimal cognitive performance, especially in attention demanding tasks. With the event-related optical signal (a mea-sure of changes in optical scattering because of neuronal activ-ity) we can characterize rapidly evolving network processes by examining the millisecond-scale temporal correlation of activity in distinct regions during the preparatory period of a response mode switching task. Participants received a precue indicating whether to respond vocally or manually. They then saw or heard the letter “L ” or “R, ” indicating a “left ” or “right ” response to be implemented with the appropriate response modality. We employed lagged cross-correlations to characterize the dynamic connectivity of preparatory processes. Our results confirmed coupling of frontal and parietal cortices and the trial-dependent relationship of the right frontal cortex with response preparation areas. The frontal-to-modality-specific cortex cross-correlations revealed a pattern in which first irrelevant regions were deacti-vated, and then relevant regions were activated. These results provide a window into the subsecond scale network interactions that flexibly tune to task demands. ■

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. *Research Highlights Transition type (switch versus repeat) influences both cue and target processing Task rule (color versus form) influences both cue and target processing Asymmetrical local switch cost originates during target but not cue processing Asymmetrical local switch cost explained by attentional effects

and feedback processing

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