All together now: when dissociations between knowledge and action disappear

Evaluating the Distinction between Cool and Hot Executive Function during Childhood

This article assesses the cool-hot executive function (EF) framework during childhood. First, conceptual analyses suggest that cool EF (cEF) is generally distinguished from hot EF (hEF). Second, both EFs can be loaded into different factors using confirmatory factor analyses. Third, the cognitive complexity of EF is similar across cEF tasks, and the cognitive complexity of cEF is similar to hEF tasks. Finally, neuroimaging analysis suggests that children activate the lateral prefrontal regions during all EF tasks. Taken together, we propose that the cool-hot framework is a useful, though not definitive way of characterizing differences in EF.

The Development of Learning, Performing, and Controlling Repeated Sequential Actions in Young Children

Our daily lives are composed of several sequential actions that we perform routinely, such as making breakfast, taking a train, and changing clothes. Previous research has demonstrated that a routine system plays a role in performing and controlling repeated sequential actions in familiar situations, and a top-down control system involves the control of the routine system in novel situations. Specifically, most developmental studies have focused on the top-down control system (e.g., executive functions) as a factor enabling the control of goal-directed actions in novel situations. Yet, it has not been thoroughly examined how young children learn, perform, and control repeated sequential actions in familiar contexts. In this review, based on recent computational accounts for adults, we highlight two critical aspects of the routine system from a developmental perspective: (1) automatic flexible changes of contextual representations, which enables humans to select context-dependent actions appropriately; and (2) detection of deviant situations, which signals the need for control to avoid errors. In addition, we propose the developmental mechanism underlying the routine system and its potential driving factors such as statistical regularities and executive functions. Finally, we suggest that an investigation into the interplay between routine and executive functions can form foundations for understanding learning, performing, and controlling repeated sequential actions in young children and discuss future directions in this area.

A Dynamical Reconceptualization of Executive-Function Development

Executive function plays a foundational role in everyday behaviors across the life span. The theoretical understanding of executive-function development, however, is still a work in progress. Doebel proposed that executive-function development reflects skills using control in the service of behavior-using mental content such as knowledge and beliefs to guide behavior in a context-specific fashion. This liberating view contrasts with modular views of executive function. This new view resembles some older dynamic-systems concepts that long ago proposed that behavior reflects the assembly of multiple pieces in context. We dig into this resemblance and evaluate what else dynamic-systems theory adds to the understanding of executive-function development. We describe core dynamic-systems concepts and apply them to executive function-as conceptualized by Doebel-and through this lens explain the multilevel nature of goal-directed behavior and how a capacity to behave in a goal-directed fashion across contexts emerges over development. We then describe a dynamic systems model of goal-directed behavior during childhood and, finally, address broader theoretical implications of dynamic-systems theory and propose new translational implications for fostering children's capacity to behave in a goal-directed fashion across everyday contexts.

Not all labels develop equally: The role of labels in guiding attention to dimensions

The emergence of cognitive flexibility is a central aspect of cognitive development during early childhood. Cognitive flexibility is often probed using verbal rules to instruct behavior. In this study, the types of labels that were provided during instruction were manipulated. In one condition, children were instructed in the standard manner with dimensional labels (e.g., "shape") and featural labels (e.g., "star"). In a second condition, children were provided only with dimensional labels. When switching to color, 4-year-olds performed equally well regardless of the type of instruction. However, when switching to shape, children perseverated at a significantly higher rate when only dimensional labels were provided. These results suggest that children's understanding of labels is a critical aspect of developing cognitive flexibility and that their understanding of the labels "shape" and "color" are different.

The effects of dual language exposure on executive function in Spanish-English bilingual children with different language abilities

The current study examined the effects of dual language exposure on executive function in 5- to 11-year-old Spanish-English bilingual children with different language skills. Dual language exposure was measured via parent report and was operationalized as the proportion of time spent in an environment where both English and Spanish were present. Executive function was measured via the Dimensional Change Card Sort (DCCS) task. Shifting costs, switching costs, and mixing costs were derived to index executive function performance. A significant interaction between extent of dual language exposure and language skills was observed such that children showed smaller shifting and mixing costs with increased dual language input as their language skills increased. The results suggest a graded effect of dual language exposure on executive function, where a robust language system may be required for dual language exposure to influence executive function.

Two-year-olds' executive functioning: The influence of task-specific vocabulary knowledge

Although many executive function (EF) tasks require only nonverbal responses, the language used by experimenters to explain the task may be important for young children's EF task performance. This study investigated how the vocabulary used in explaining an EF task affects 2-year-olds' performance. Experiment 1 used the standard instructions for the Reverse Categorization Task, in which children are asked to sort different-sized blocks into different-sized buckets according to one rule and then switch to a new rule. In Experiment 2, the task remained the same, but different instructions requiring less knowledge of size words were used. Children's productive vocabulary was assessed in both experiments but was only correlated with task performance in Experiment 1. These results suggest that task-specific vocabulary knowledge may play a role in children's performance on tasks designed to measure nonverbal cognitive ability.

Sustained selective attention predicts flexible switching in preschoolers

Stability and flexibility are fundamental to an intelligent cognitive system. Here, we examined the relationship between stability in selective attention and explicit control of flexible attention. Preschoolers were tested on the Dimension Preference (DP) task, which measures the stability of selective attention to an implicitly primed dimension, and the Dimension Change Card Sort (DCCS) task, which measures flexible attention switching between dimensions. Children who successfully switched on the DCCS task were more likely than those who perseverated to sustain attention to the primed dimension on the DP task across trials. We propose that perseverators have less stable attention and distribute their attention between dimensions, whereas switchers can successfully stabilize attention to individual dimensions and, thus, show more enduring priming effects. Flexible attention may emerge, in part, from implicit processes that stabilize attention even in tasks not requiring switching.

Cognitive Control of Sequential Knowledge in 2-Year-Olds

Under incidental instructions, thirty-eight 2-year-olds were trained on a six-element deterministic sequence of spatial locations. Following training, subjects were informed of the presence of a sequence and asked to either reproduce or suppress the learned material. Children's production of the trained sequence was modulated by these instructions. When asked to suppress the trained sequence, the children were able to increase generation of paths that were not from the training sequence. Their performance was thus dependent on active suppression of knowledge, rather than on a random generation strategy. This degree of control in 2-year-olds stands in stark contrast to 3-year-olds∗ failure to control explicitly instructed rule-based knowledge (as measured by the dimensional-change card-sort task). We suggest that the incidental nature of a learning episode enables the acquisition of a more procedural form of knowledge with which this age group has more experience prior to the onset of fluent language.

Seeing conflict and engaging control: Experience with contrastive language benefits executive function in preschoolers

Engaging executive function often requires overriding a prepotent response in favor of a conflicting but adaptive one. Language may play a key role in this ability by supporting integrated representations of conflicting rules. We tested whether experience with contrastive language that could support such representations benefits executive function in 3-year-old children. Children who received brief experience with language highlighting contrast between objects, attributes, and actions showed greater executive function on two of three 'conflict' executive function tasks than children who received experience with contrasting stimuli only and children who read storybooks with the experimenter, controlling for baseline executive function. Experience with contrasting stimuli did not benefit executive function relative to reading books with the experimenter, indicating experience with contrastive language, rather than experience with contrast generally, was key. Experience with contrastive language also boosted spontaneous attention to contrast, consistent with improvements in representing contrast. These findings indicate a role for language in executive function that is consistent with the Cognitive Complexity and Control theory's key claim that coordinating conflicting rules is critical to overcoming perseveration, and suggest new ideas for testing theories of executive function.

A meta-analysis of the Dimensional Change Card Sort: Implications for developmental theories and the measurement of executive function in children

The Dimensional Change Card Sort (DCCS) is a widely used measure of executive function in children. In the standard version, children are shown cards depicting objects that vary on two dimensions (e.g., colored shapes such as red rabbits and blue boats), and are told to sort them first by one set of rules (e.g., shape) and then by another (e.g., color). Most 3-year-olds persist in sorting by the pre-switch rules, whereas 5-year-olds switch flexibly. We conducted a meta-analysis of standard and experimental versions of the task (N = 69 reports, 426 conditions) to examine the influence of diverse task variations on performance. Age, how the test stimuli were labeled for the child, emphasis on conflict in the verbal introduction of the post-switch rules, and the number of pre-switch trials each independently predicted switching on the standard DCCS, whereas pre-switch feedback, practice, and task modality did not. Increasing the relative salience of the post-switch dimension was associated with higher rates of switching, and, conversely, decreasing post-switch salience was associated with lower rates of switching, and under both kinds of manipulation performance continued to be associated with age. Spatially separating the dimensional values was associated with higher rates of switching, and it was confirmed that the degree of spatial separation matters, with children benefiting most when the dimensional values are fully spatially segregated. Switch rates tended to be higher in versions on which children were prompted to label the stimuli compared to when the experimenter provided labels, and lower when reversal instructions were used in conjunction with the standard task stimuli. Theoretical and practical implications for the study and measurement of executive function in early childhood are discussed.

Executive Function Development

Emerging executive function in childhood, one of the main predictors of major life success, is goal-directed in nature. Yet children’s ability to identify goals (i.e., what should be done) has been underresearched, often because of implicit assumptions that it is trivial even in early childhood. In contrast, I review evidence for goal identification as a major force behind developing executive function. Both increasing attention to environmental cues and increased goal inferencing from these cues drive goal-identification improvement with age. This framework has important implications for assessing and supporting executive function in childhood.

The cost of learning: interference effects in memory development

Learning often affects future learning and memory for previously learned information by exerting either facilitation or interference effects. Several theoretical accounts of interference effects have been proposed, each making different developmental predictions. This research examines interference effects across development, with the goal of better understanding mechanisms of interference and of memory development. Preschool-aged children and adults participated in a 3-phased associative learning paradigm containing stimuli that were either unique or repeated across phases. Both age groups demonstrated interference effects, but only for repeated items. Whereas proactive interference effects were comparable across age groups, retroactive interference reached catastrophic-like levels in children. Additionally, retroactive interference increased in adults when contextual differences between phases were minimized (Experiment 2), and decreased in adults who were more successful at encoding repeated pairs of stimuli during a training phase (Experiment 3). These results are discussed with respect to theories of memory and memory development.

Bottom-up and top-down dynamics in young children's executive function: Labels aid 3-year-olds' performance on the Dimensional Change Card Sort

Executive function (EF) improves between the ages of 3 and 5 and has been assessed reliably using the Dimensional Change Card Sort (DCCS), a task in which children first sort bivalent cards by one dimension (e.g., shape) and then are instructed to sort by a different dimension (e.g., color). Three-year-olds typically perseverate on the pre-switch dimension, whereas 5-year-olds switch flexibly. Labeling task stimuli can facilitate EF performance (Jacques & Zelazo, 2005; Kirkham, Cruess, & Diamond, 2003), but the nature of this effect is unclear. In 3 experiments we examined 2 hypotheses deriving from different theoretical perspectives: first, that labels facilitate performance in a more bottom-up fashion, by biasing attention to relevant task rules (Kirkham et al., 2003); and second, that labels aid performance in a more top-down fashion by prompting reflection and an understanding of the hierarchical nature of the task (Zelazo, 2004). Children performed better on the DCCS when labels referred to the relevant sorting dimension (Experiment 1). This was a function of the content of the labels rather than the change in auditory signal across phases (Experiment 2). Furthermore, labeling the opposite dimension only did not have a symmetrically negative effect on performance (Experiment 3). Together, these results suggest external, verbal labels bias children to attend to task-relevant information, likely through interaction with emerging top-down, endogenous control.

Adjusting behavior to changing environmental demands with development

Plasticity refers to changes in the brain that enable an organism to adapt its behavior in the face of changing environmental demands. The evolutionary role of plasticity is to provide the cognitive flexibility to learn from experiences, to monitor the world based on learned predictions, and adjust actions when these predictions are violated. Both progressive (myelination) and regressive (synaptic pruning) brain changes support this type of adaptation. Experience-driven changes in neural connections underlie the ability to learn and update thoughts and behaviors throughout life. Many cognitive and behavioral indices exhibit nonlinear life-span trajectories, suggesting the existence of specific sensitive developmental periods of heightened plasticity. We propose that age-related differences in learning capabilities and behavioral performance reflect the distinct maturational timetable of subcortical learning systems and modulatory prefrontal regions. We focus specifically on the developmental transition of adolescence, during which individuals experience difficulty flexibly adjusting their behavior when confronted with unexpected and emotionally salient events. In this article, we review the findings illustrating this phenomenon and how they vary by individual.

Dual routes to cognitive flexibility: learning and response-conflict resolution in the dimensional change card sort task

Cognitive control, the ability to align our actions with goals or context, is largely absent in children under four. How then are preschoolers able to tailor their behavior to best match the situation? Learning may provide an alternative route to context-sensitive responding. This study investigated this hypothesis in the Dimensional Change Card Sort (DCCS), a classic test of cognitive control that most under-fours fail. A training intervention based on learning theoretic principles proved highly effective: Three-year-olds who learned about DCCS rules and game contexts in a card-labeling task, subsequently transferred this knowledge to sorting in the DCCS, passing at more than 3 times the rate of controls (N = 47). This surprising finding reveals much about the nature of the developing mind.

Why won't you do what I want? The informative failures of children and models

Computational models are powerful tools - too powerful, according to some. We argue that the idea that models can "do anything" is wrong, and describe how their failures have been informative. We present new work showing surprising diversity in the effects of feedback on children's task-switching, such that some children perseverate despite this feedback, other children switch as instructed, and yet others play an "opposites" game without truly switching to the newly-instructed task. We present simulations that demonstrate the failure of an otherwise-successful neural network model to capture this failure of children. Simulating this pattern motivates the inclusion of updating mechanisms that make contact with a growing literature on frontostriatal function, despite their absence in extant theories of the development of cognitive flexibility. We argue from this and other examples that computational models are more constrained than is typically acknowledged, and that their resulting failures can be theoretically illuminating.

Developing Cognitive Control: Three Key Transitions

The ability to flexibly break out of routine behaviors develops gradually and is essential for success in life. We discuss three key developmental transitions toward more flexible behavior. First, children develop an increasing ability to overcome habits by engaging cognitive control in response to environmental signals. Second, children shift from recruiting cognitive control reactively, as needed in the moment, to recruiting cognitive control proactively, in preparation for needing it. Third, children shift from relying on environmental signals for engaging cognitive control to becoming more self-directed. All three transitions can be understood in terms of the development of increasingly active and abstract goal representations in prefrontal cortex.

When seeing is knowing: the role of visual cues in the dissociation between children's rule knowledge and rule use

The Dimensional Change Card Sort (DCCS) task requires children to switch from sorting cards based on shape or color to sorting based on the other dimension. Typically, 3-year-olds perseverate, whereas 4-year-olds flexibly sort by different dimensions. Zelazo and colleagues (1996, Cognitive Development, 11, 37-63) asked children questions about the postswitch rules and found an apparent dissociation between rule knowledge and rule use, namely that 3-year-olds demonstrate accurate knowledge of the postswitch rules despite sorting cards incorrectly. Here, we show that children's success with these questions is grounded in their use of available visual cues; children who fail sorting use the target cards to correctly answer questions, and when the cards are unavailable they guess. This suggests that there might not be a dissociation between children's rule knowledge and rule use in the DCCS.

N2 amplitude as a neural marker of executive function in young children: an ERP study of children who switch versus perseverate on the Dimensional Change Card Sort

To explore the neurocognitive mechanisms underlying individual differences in executive function during the preschool years, high-density electroencephalography (EEG) was used to record event-related potentials (ERPs) from 99 children (between 35 and 54 months of age) during performance on the Dimensional Change Card Sort (DCCS), a widely used measure of executive function in which participants are required to sort bivalent stimuli first by one dimension and then by another. ERP analyses comparing children who switched flexibly (passed) to those who perseverated on post-switch trials (failed) focused on the N2 component, which was maximal over fronto-central sites. N2 amplitude was smaller (less negative) for children who passed the DCCS than for children who failed, suggesting that the N2, often associated with conflict monitoring, may serve as a neural marker of individual differences in executive function. Implications for learning and education are discussed.

Perseveration and the status of 3-year-olds' knowledge in a card-sorting task: evidence from studies involving congruent flankers

Infants and young children often perseverate despite apparent knowledge of the correct response. Two Experiments addressed questions concerning the status of such knowledge in the context of a card-sorting task. In Experiment 1, three groups of 3-year-olds sorted bivalent cards one way and then were instructed to switch and sort the same cards using new rules under varying conditions of support offered by congruent flankers. Although formal aspects of the task such as higher-order rule use, stimulus redescription, and dimensional shifting remained constant across all conditions, use of the new rules increased with parametric increases in environmental support for the use of the new rules. In Experiment 2, 3-year-olds were more likely to switch and use new rules when test stimuli were flanked by congruent flankers rather than neutral flankers, even though both conditions made equivalent demands on attentional inhibition. Thus, in both experiments, children's knowledge of the new rules proved to be adequate under less demanding conditions but inadequate under more demanding conditions. These findings are consistent with the idea that children's knowledge is graded in strength rather than present or absent.

Behavioral assessment of emotion discrimination, emotion regulation, and cognitive control in childhood, adolescence, and adulthood

Emotion discrimination, emotion regulation, and cognitive control are three related, yet separable processes that emerge over the course of development. The current study tested 100 children, adolescents, and adults on an Emotional Go/Nogo task, illustrating the ability of this paradigm to identify the unique developmental patterns for each of these three processes in the context of both positive (happy) and negative emotions (fear, sad, and anger), across three different age groups. Consistent with previous literature, our findings show that emotion discrimination and regulatory abilities (both cognitive control and emotion regulation) improve steadily for each age group, with each age group showing unique patterns of performance. The findings suggest that emotion regulation is constructed from basic cognition control and emotion discrimination skills. The patterns of behavior from the Emotional Go/Nogo task provide normative benchmark data across a wide range of emotions that can be used for future behavioral and neuroimaging studies that examine the developmental construction of emotion regulatory processes.

Braking and Accelerating of the Adolescent Brain

Adolescence is a developmental period often characterized as a time of impulsive and risky choices leading to increased incidence of unintentional injuries and violence, alcohol and drug abuse, unintended pregnancy and sexually transmitted diseases. Traditional neurobiological and cognitive explanations for such suboptimal choices and actions have failed to account for nonlinear changes in behavior observed during adolescence, relative to childhood and adulthood. This review provides a biologically plausible conceptualization of the mechanisms underlying these nonlinear changes in behavior, as an imbalance between a heightened sensitivity to motivational cues and immature cognitive control. Recent human imaging and animal studies provide a biological basis for this view, suggesting differential development of subcortical limbic systems relative to top-down control systems during adolescence relative to childhood and adulthood. This work emphasizes the importance of examining transitions into and out of adolescence and highlights emerging avenues of future research on adolescent brain development.

Moderate vagal withdrawal in 3.5-year-old children is associated with optimal performance on executive function tasks

Vagal tone (measured via respiratory sinus arrhythmia, RSA) and vagal withdrawal (measured by decreases in RSA) have been identified as physiological measures of self-regulation, but little is known how they may relate to the regulation of cognitive activity as measured through executive function (EF) tasks. We expected that baseline measures of vagal tone, thought to be an indicator of attention, would correlate with EF performance. We also predicted that vagal withdrawal would allow for the reorientation of attention that is needed to succeed on EF tasks, but too much withdrawal would be detrimental. RSA measured at baseline was indeed related to EF performance in 220 3.5-year-old children, and those who exhibited a moderate decrease in RSA during the EF tasks outperformed children whose RSA decreased by too little or too much. These findings implicate vagal tone withdrawal as a psychophysiological measure of higher cognitive processes, most likely substantiated through increases in the levels of focused attention.

Selective attention and attention switching: towards a unified developmental approach

We review and relate two literatures on the development of attention in children: one concerning flexible attention switching and the other concerning selective attention. The first is a growing literature on preschool children's performances in an attention-switching task indicating that children become more flexible in their attentional control during the preschool years. The second literature encompasses a large and robust set of phenomena for the same developmental period that indicates a protracted course of development for selective attention in children. We ask whether developmental changes in processes of selective attention may contribute to more flexible attention switching. We consider the two sets of phenomena with respect to this question and propose an empirical agenda for their joint study that may lead ultimately to a unified account of the development of selective attention and attention switching.

When simple things are meaningful: working memory strength predicts children's cognitive flexibility

People often perseverate, repeating outdated behaviors despite correctly answering questions about rules they should be following. Children who perseverate are slower to respond to such questions than children who successfully switch to new rules, even after controlling for age and processing speed. Thus, switchers may have stronger working memory strength than perseverators, with stronger rule representations supporting both flexible switching and faster responses to questions. Alternatively, better inhibitory abilities may support switchers' faster responses by helping to resolve conflict. The current study tested these accounts using a new one-dimensional card sort. Even with all possible sources of conflict removed, switchers still responded faster than perseverators to questions about rules, supporting the graded working memory account.

A hierarchical competing systems model of the emergence and early development of executive function

The hierarchical competing systems model (HCSM) provides a framework for understanding the emergence and early development of executive function--the cognitive processes underlying the conscious control of behavior--in the context of search for hidden objects. According to this model, behavior is determined by the joint influence of a developmentally invariant habit system and a conscious representational system that becomes increasingly influential as children develop. This article describes a computational formalization of the HCSM, reviews behavioral and computational research consistent with the model, and suggests directions for future research on the development of executive function.

A hierarchical competing systems model of the emergence and early development of executive function

The hierarchical competing systems model (HCSM) provides a framework for understanding the emergence and early development of executive function--the cognitive processes underlying the conscious control of behavior--in the context of search for hidden objects. According to this model, behavior is determined by the joint influence of a developmentally invariant habit system and a conscious representational system that becomes increasingly influential as children develop. This article describes a computational formalization of the HCSM, reviews behavioral and computational research consistent with the model, and suggests directions for future research on the development of executive function.

A hierarchical competing systems model of the emergence and early development of executive function

The hierarchical competing systems model (HCSM) provides a framework for understanding the emergence and early development of executive function--the cognitive processes underlying the conscious control of behavior--in the context of search for hidden objects. According to this model, behavior is determined by the joint influence of a developmentally invariant habit system and a conscious representational system that becomes increasingly influential as children develop. This article describes a computational formalization of the HCSM, reviews behavioral and computational research consistent with the model, and suggests directions for future research on the development of executive function.

Cognitive flexibility in preschoolers: the role of representation activation and maintenance

Preschoolers' lack of cognitive flexibility has often been attributed to perseverative processing. This study investigates alternative potential sources of difficulty such as deficits in activating previously ignored information and in maintaining currently relevant information. In Experiment 1, a new task tapping attentional switching was designed to isolate the difficulty of overriding an initial representation, that is, perseverative processing ('Perseveration' version), and the difficulty of activating a previously ignored representation, that is, activation deficit ('Activation-deficit' version). Three-year-olds' performance suggested that inflexibility may primarily stem from an activation deficit. Control experiments confirmed that the difficulty of the 'Activation-deficit' version could not be attributed to the effect of attraction to novelty. In Experiment 2, 'distraction' errors, alleged to reflect a failure to maintain a relevant representation, and 'perseverative' errors were distinguished. The results highlighted the important role of representation maintenance in flexibility. The present study indicates that preschoolers' lack of cognitive flexibility is multi-determined and prompts us to reconsider the role of perseveration.

The adolescent brain

Adolescence is a developmental period characterized by suboptimal decisions and actions that are associated with an increased incidence of unintentional injuries, violence, substance abuse, unintended pregnancy, and sexually transmitted diseases. Traditional neurobiological and cognitive explanations for adolescent behavior have failed to account for the nonlinear changes in behavior observed during adolescence, relative to both childhood and adulthood. This review provides a biologically plausible model of the neural mechanisms underlying these nonlinear changes in behavior. We provide evidence from recent human brain imaging and animal studies that there is a heightened responsiveness to incentives and socioemotional contexts during this time, when impulse control is still relatively immature. These findings suggest differential development of bottom-up limbic systems, implicated in incentive and emotional processing, to top-down control systems during adolescence as compared to childhood and adulthood. This developmental pattern may be exacerbated in those adolescents prone to emotional reactivity, increasing the likelihood of poor outcomes.

Bilingual experience and executive functioning in young children

Advanced inhibitory control skills have been found in bilingual speakers as compared to monolingual controls (Bialystok, 1999). We examined whether this effect is generalized to an unstudied language group (Spanish-English bilingual) and multiple measures of executive function by administering a battery of tasks to 50 kindergarten children drawn from three language groups: native bilinguals, monolinguals (English), and English speakers enrolled in second-language immersion kindergarten. Despite having significantly lower verbal scores and parent education/income level, Spanish-English bilingual children's raw scores did not differ from their peers. After statistically controlling for these factors and age, native bilingual children performed significantly better on the executive function battery than both other groups. Importantly, the relative advantage was significant for tasks that appear to call for managing conflicting attentional demands (Conflict tasks); there was no advantage on impulse-control (Delay tasks). These results advance our understanding of both the generalizability and specificity of the compensatory effects of bilingual experience for children's cognitive development.

Why do children perseverate when they seem to know better: graded working memory, or directed inhibition?

Children sometimes have trouble switching from one task to another, despite demonstrating an awareness of current task demands. This behavior could reflect problems either directly inhibiting previously relevant information or sufficiently activating graded working me mory representations forthe current task. We tested competing predictions from each account, using a computerized card-sorting task in which we assessed children's task switching abilities and their response speed to simple questions about current task demands. All children answered these questions correctly, but children who successfully switched tasks responded more quickly to questions than did children who perseverated on previous tasks, even after factoring out processing speed and age. This reaction time difference supports graded working memory accounts, with stronger representations of current task demands aiding both task-switching and responses to questions. This result poses a challenge for directed inhibition accounts, because nothing needs to be inhibited to answer simple questions that lack conflicting information.

The adolescent brain

Adolescence is a developmental period characterized by suboptimal decisions and actions that give rise to an increased incidence of unintentional injuries and violence, alcohol and drug abuse, unintended pregnancy and sexually transmitted diseases. Traditional neurobiological and cognitive explanations for adolescent behavior have failed to account for the nonlinear changes in behavior observed during adolescence, relative to childhood and adulthood. This review provides a biologically plausible conceptualization of the neural mechanisms underlying these nonlinear changes in behavior, as a heightened responsiveness to incentives while impulse control is still relatively immature during this period. Recent human imaging and animal studies provide a biological basis for this view, suggesting differential development of limbic reward systems relative to top-down control systems during adolescence relative to childhood and adulthood. This developmental pattern may be exacerbated in those adolescents with a predisposition toward risk-taking, increasing the risk for poor outcomes.

Use it or lose it: examining preschoolers' difficulty in maintaining and executing a goal

Individuals with low working memory capacity (e.g. preschoolers) are more prone to goal neglect, or a failure to execute a goal even though it is understood. We examined the role of goal neglect in performance on the Dimensional Change Card Sort by including 'redundant' cards that could be sorted without attending to the rules, as well as the traditional 'conflict' cards that encouraged awareness of the rules. In Experiment 1, 4- and 5-year-old children were administered two card sorts that differed on the proportion of redundant cards presented (20% vs. 80%). Children neglected the goal more often when faced with a preponderance of redundant cards, suggesting that consistent attention to the rules leads to goal maintenance. In Experiment 2, results were replicated even when the post-switch rules were repeated on every trial. Implications for the development of working memory are discussed.