Reactive and proactive control processes in voluntary task choice.

Deciding which task to perform when multiple tasks are available can be influenced by external influences in the environment. In the present study, we demonstrate that such external biases on task-choice behavior reflect reactive control adjustments instead of a failure in control to internally select a task goal. Specifically, in two experiments we delayed the onset of one of two task stimuli by a short (50 ms), medium (300 ms), or long (1,000 ms) stimulus-onset asynchrony (SOA) within blocks while also varying the relative frequencies of short versus long SOAs across blocks (i.e., short SOA frequent vs. long SOA frequent). Participants' task choices were increasingly biased towards selecting the task associated with the first stimulus with increasing SOAs. Critically, both experiments also revealed that the short-to-medium SOA bias was larger in blocks with more frequent long SOAs when participants had limited time to prepare for an upcoming trial. When time to select an upcoming task was extended in Experiment 2, this interaction was not significant, suggesting that the extent to which people rely on reactive control adjustments is additionally modulated by proactive control processes. Thus, the present findings also suggest that voluntary task choices are jointly guided by both proactive and reactive processes, which are likely to adjust the relative activation of different task goals in working memory.

Integrating cognition in the laboratory with cognition in the real world: the time cognition takes, task fidelity, and finding tasks when they are mixed together.

It is now possible for real-life activities, unfolding over their natural range of temporal and spatial scales, to become the primary targets of cognitive studies. Movement toward this type of research will require an integrated methodological approach currently uncommon in the field. When executed hand in hand with thorough and ecologically valid empirical description, properly developed laboratory tasks can serve as model systems to capture the essentials of a targeted real-life activity. When integrated together, data from these two kinds of studies can facilitate causal analysis and modeling of the mental and neural processes that govern that activity, enabling a fuller account than either method can provide on its own. The resulting account, situated in the activity's natural environmental, social, and motivational context, can then enable effective and efficient development of interventions to support and improve the activity as it actually unfolds in real time. We believe that such an integrated multi-level research program should be common rather than rare and is necessary to achieve scientifically and societally important goals. The time is right to finally abandon the boundaries that separate the laboratory from the outside world.

Assessing the role of reward in task selection using a reward-based voluntary task switching paradigm.

People exhibit a remarkable ability to both maintain controlled focus on executing a single task and flexibly shift between executing several tasks. Researchers studying human multitasking have traditionally focused on the cognitive control mechanisms that allow for such stable and flexible task execution, but there has been a recent interest in how cognitive control mechanisms drive the decision of task selection. The present research operationalizes a foraging analogy to investigate what factors drive the decision to either exploit task repetitions or explore task switches. A novel paradigm-reward-based voluntary task switching-ascribes point values to tasks where the overall goal is to accumulate points as quickly as possible. The reward structure generally rewards switching tasks, thereby juxtaposing the motivation to gain increased reward (by exploring task switches) against the motivation to perform quickly (by exploiting task repetitions). Results suggest that people are highly sensitive to changes in both reward and effort demands when making task selections, and that the task selection process is efficient and flexible. We argue that a cost-benefit mechanism might underlie decisions in multitasking contexts, whereby people compute task selections based on both the reward available for selecting a task and the effort necessary to execute a task.

Task frequency influences stimulus-driven effects on task selection during voluntary task switching.

Task selection during voluntary task switching involves both top-down (goal-directed) and bottom-up (stimulus-driven) mechanisms. The factors that shift the balance between these two mechanisms are not well characterized. In the present research, we studied the role that task frequency plays in determining the extent of stimulus-driven task selection. In two experiments, we used the basic paradigm adapted from Arrington (Memory & Cognition, 38, 991-997, 2008), in which the effect of stimulus availability serves as a marker of stimulus-driven task selection. A number and letter appeared on each trial with varying stimulus onset asynchronies, and participants performed either a consonant/vowel or an even/odd judgment. In Experiment 1, participants were instructed as to the relative frequency with which each task was to be performed (i.e., 50/50, 60/40, or 75/25) and were further instructed to make their transitions between tasks unpredictable. In Experiment 2, participants were given no instructions about how to select tasks, resulting in naturally occurring variation in task frequency. With both instructed (Exp. 1) and naturally occurring (Exp. 2) relative task frequencies, the less frequently performed task showed a greater effect of stimulus availability on task selection, suggestive of a larger influence of stimulus-driven mechanisms during task performance for the less frequent task. When goal-directed mechanisms of task choice are engaged less frequently, the relative influence of the stimulus environment increases.

Encoding and choice in the task span paradigm.

Cognitive control during sequences of planned behaviors requires both plan-level processes such as generating, maintaining, and monitoring the plan, as well as task-level processes such as selecting, establishing and implementing specific task sets. The task span paradigm (Logan in J Exp Psychol Gen 133:218-236, 2004) combines two common cognitive control paradigms, task switching and working memory span, to investigate the integration of plan-level and task-level processes during control of sequential behavior. The current study expands past task span research to include measures of encoding processes and choice behavior with volitional sequence generation, using the standard task span as well as a novel voluntary task span paradigm. In two experiments, we consider how sequence complexity, defined separately for plan-level and task-level complexity, influences sequence encoding (Experiment 1), sequence choice (Experiment 2), sequence memory, and task performance of planned sequences of action. Results indicate that participants were sensitive to sequence complexity, but that different aspects of behavior are most strongly influenced by different types of complexity. Hierarchical complexity at the plan level best predicts voluntary sequence generation and memory; while switch frequency at the task level best predicts encoding of externally defined sequences and task performance. Furthermore, performance RTs were similar for externally and internally defined plans, whereas memory was improved for internally defined sequences. Finally, participants demonstrated a significant sequence choice bias in the voluntary task span. Consistent with past research on choice behavior, volitional selection of plans was markedly influenced by both the ease of memory and performance.

Rethinking volitional control over task choice in multitask environments: use of a stimulus set selection strategy in voluntary task switching.

Under conditions of volitional control in multitask environments, subjects may engage in a variety of strategies to guide task selection. The current research examines whether subjects may sometimes use a top-down control strategy of selecting a task-irrelevant stimulus dimension, such as location, to guide task selection. We term this approach a stimulus set selection strategy. Using a voluntary task switching procedure, subjects voluntarily switched between categorizing letter and number stimuli that appeared in two, four, or eight possible target locations. Effects of stimulus availability, manipulated by varying the stimulus onset asynchrony between the two target stimuli, and location repetition were analysed to assess the use of a stimulus set selection strategy. Considered across position condition, Experiment 1 showed effects of both stimulus availability and location repetition on task choice suggesting that only in the 2-position condition, where selection based on location always results in a target at the selected location, subjects may have been using a stimulus set selection strategy on some trials. Experiment 2 replicated and extended these findings in a visually more cluttered environment. These results indicate that, contrary to current models of task selection in voluntary task switching, the top-down control of task selection may occur in the absence of the formation of an intention to perform a particular task.

Biasing free choices: the role of the rostral cingulate zone in intentional control.

Humans have the ability to choose freely between different alternatives. It is common knowledge, however, that our free choices are influenced by the environment and by past experiences. In the present study we investigated if the involvement of the medial frontal cortex, which is known to be important for intentional control, depends on whether free choices are biased by past experiences. By using fMRI, we observed that the rostral cingulate zone (RCZ) is less activated during biased than during unbiased choices. On the basis of this finding we argue that the RCZ plays a specific role in intentional control of action by evaluating which alternative is most appropriate in a given context. In addition, we observed that free choices were biased more during mind wandering episodes than during on-task episodes. This finding suggests that during periods of mind wandering, attention is shifted away from the primary task and external factors can influence the choice process more easily.

The effect of hierarchical task representations on task selection in voluntary task switching.

The current study explored the potential for hierarchical representations to influence action selection during voluntary task switching. Participants switched between 4 individual task elements. In Experiment 1, participants were encouraged to represent the task elements as grouped within a hierarchy based on experimental manipulations of varying complexity. Manipulations implemented only during the practice phase of the experiment failed to influence action selection; however, manipulations that persisted throughout the experiment influenced action selection in a manner suggestive of a hierarchical task representation. Experiment 2 demonstrated that, once established, the influences of hierarchical representations appear to persist, regardless of whether they are required. The results suggest that hierarchical representations may play a functional role of goal shielding in action selection.

A thalamocorticostriatal dopamine network for psychostimulant-enhanced human cognitive flexibility.

BACKGROUND: Everyday life demands continuous flexibility in thought and behavior. We examined whether individual differences in dopamine function are related to variability in the effects of amphetamine on one aspect of flexibility: task switching. METHODS: Forty healthy human participants performed a task-switching paradigm following placebo and oral amphetamine administration. [(18)F]fallypride was used to measure D2/D3 baseline receptor availability and amphetamine-stimulated dopamine release. RESULTS: The majority of the participants showed amphetamine-induced benefits through reductions in switch costs. However, such benefits were variable. Individuals with higher baseline thalamic and cortical receptor availability and striatal dopamine release showed greater reductions in switch costs following amphetamine than individuals with lower levels. The relationship between dopamine receptors and stimulant-enhanced flexibility was partially mediated by striatal dopamine release. CONCLUSIONS: These data indicate that the impact of the psychostimulant on cognitive flexibility is influenced by the status of dopamine within a thalamocorticostriatal network. Beyond demonstrating a link between this dopaminergic network and the enhancement in task switching, these neural measures accounted for unique variance in predicting the psychostimulant-induced cognitive enhancement. These results suggest that there may be measurable aspects of variability in the dopamine system that predispose certain individuals to benefit from and hence use psychostimulants for cognitive enhancement.

Working memory capacity modulates task performance but has little influence on task choice.

Variation in the ability to maintain internal goals while resolving competition from multiple information streams has been related to individual differences in working memory capacity (WMC). In a multitask environment, task choice and task performance are influenced by internal goals, prior behavior within the environment, and the availability of relevant and irrelevant information in the environment. Using the voluntary task-switching procedure, task performance, as measured by switch costs, was related to WMC, but only at short preparation intervals. Task choice processes were only weakly related to WMC. These findings are consistent with models of cognitive control that separate task choice processes from the processes of activating and maintaining task readiness. WMC is related to regulation of specific task parameters but not to choice processes integral to the coordination of multiple sources of information.

Stimulus-based priming of task choice during voluntary task switching.

Two voluntary task-switching experiments probed the influence of previous exposures to stimuli and categorizations of these stimuli on task choice during subsequent exposures to the same stimuli. Subjects performed origin and size judgments under standard voluntary task-switching instructions to perform the tasks equally often in a random order. Both when subjects voluntarily selected the task on the first exposure (Experiment 1) and when the experimenter manipulated the task on the first exposure (Experiment 2), subjects chose to perform the same task on subsequent exposures significantly more often than would be expected on the basis of the instructions to perform tasks in a random order. Presentation of a previously encountered stimulus may result in the retrieval of a stimulus-task binding or event file that biases task selection as well as task readiness. The pattern of data across the 2 experiments suggests that stimulus-based priming influences task choice through both retrieval of episodes within the context of the experiment and semantic memory mechanisms.

What's on your mind: the influence of the contents of working memory on choice.

Information maintained in working memory (WM) has the potential to bias selective attention and limit executive attention. The current study assessed the influence of information in WM on the tasks one chooses to perform in a multitasking environment. Participants held either identities or locations in WM while performing voluntary task-switching trials on stimuli that did or did not match the information they were attempting to maintain. A bias toward performing the task associated with stimuli that had recently been encoded into WM was found. The results suggest that information in WM can influence choice within a multitasking environment.

Perceptual asymmetries influence task choice: the effect of lateralised presentation of hierarchical stimuli.

The current study examined how hemispheric asymmetries in perceptual processing affect control processes associated with voluntary task choice during multitask behaviour. In a voluntary task-switching paradigm, where participants are free to choose which task to perform on each trial, participants identified either the global-or local-level features of hierarchical stimuli presented to either the left or right visual field. Hemispheric asymmetries in perception of lateralised hierarchical stimuli were evident in reaction times. Importantly, participants were more likely to categorize the stimulus in line with the processing efficiency of the hemisphere to which it was initially presented: the global task for left visual field presentation and the local task for right visual field presentation. Perceptual processing characteristics influence control processes associated with task choice in multitask environments.

The role of attentional networks in voluntary task switching.

Coordination of task choice and performance in multitask environments likely involves attentional processes. Subjects completed the Attention Network Test (ANT) and a voluntary task-switching procedure. Task choice, but not task performance, was correlated with the executive score from the ANT, with higher switch probabilities for subjects with more efficient executive control networks. Task performance was correlated with the alerting score, with larger response time switch costs for subjects with larger alerting scores. The dissociation of task choice and task performance measures in terms of the pattern of correlations with attentional networks suggests that these two measures may reflect different cognitive processes engaged in voluntary task switching.

The effect of stimulus availability on task choice in voluntary task switching.

The voluntary task switching paradigm allows subjects to choose which task to perform on each trial in a stimulus environment affording multiple tasks. The present study examined the effect of stimulus availability on task choice. Subjects viewed displays containing a digit and a letter and performed either an even/odd or a consonant/vowel judgment on each trial. The target stimuli appeared with a stimulus onset asynchrony (SOA) of 0, 50, 100, or 150 msec. The probability of performing the task associated with Stimulus 1 increased as SOA increased, indicating an effect of external or stimulus-driven factors on task choice. This effect of stimulus availability on task choice was greater when the response-stimulus interval was 400 msec than when it was 2,000 msec. This interaction of preparation interval and stimulus availability is explained within a model of task choice that includes both internal processes and external influences.

Separating cue encoding from target processing in the explicit task-cuing procedure: are there "true" task switch effects?

Six experiments were conducted to separate cue encoding from target processing in explicitly cued task switching to determine whether task switch effects could be separated from cue encoding effects and to determine the nature of the representations produced by cue encoding. Subjects were required to respond to the cue, indicating which cue was presented (Experiments 1, 3a, and 4a) or which task was cued (Experiments 2, 3b, and 4b), before performing the cued task on the target. Cue encoding was successfully separated from target processing when the cue response indicated which task was cued but not when it indicated which cue was presented. Task switch effects were found when this separation was successful, suggesting that there are "true" task switch effects independent of cue encoding. Analysis of the conditions required for successful separation suggested that cue encoding results in a semantic categorical representation of the task to be performed rather than verbal or phonological representations of individual cues. Implications for the authors' past modeling of task-switching performance are discussed.

Voluntary task switching: chasing the elusive homunculus.

In the voluntary task switching procedure, subjects choose the task to perform on a series of bivalent stimuli, requiring top-down control of task switching. Experiments 1-3 contrasted voluntary task switching and explicit task cuing. Choice behavior showed small, inconsistent effects of external stimulus characteristics, supporting the assumption of top-down control of task choice. Switch costs were smaller when subjects chose to switch tasks than when instructed by an external cue. Experiments 4-6 separated choice costs from switch costs. These findings support models of task switching that incorporate top-down processes in accounts of switch costs. The degree to which task switching procedures capture top-down versus bottom-up processes may depend on the extent of environmental support provided by the procedure.

The cost of a voluntary task switch.

Task-switching paradigms are widely used to study executive control. However, standard paradigms may not require active control to switch tasks. We examined voluntary task switching by having subjects choose which task to perform on a series of bivalent stimuli. Subjects performed parity or magnitude judgments on single digits. Instructions were to perform the two tasks equally often and in a random order. The response-to-stimulus interval (RSI) was either 100 or 1,000 ms, manipulated between blocks. Task alternations were slower than task repetitions, and this switch cost was greater at the short RSI than at the long RSI (310 and 94 ms, respectively). Additionally, subjects produced more task repetitions than expected if the tasks were performed in a random sequence. These results show costs associated with a voluntary task switch, when subjects must actively control the choice of the task to be performed.

Episodic and semantic components of the compound-stimulus strategy in the explicit task-cuing procedure.

The explicit task-cuing procedure is commonly used to study executive control processes involved in set switching, but performance in this task-switching procedure may be accomplished without switching tasks. Subjects may perform both tasks by using a compound-stimulus strategy, in which subjects encode the cue, encode the target, and use the combination as a compound retrieval cue to choose the appropriate response. We manipulated the number of targets (8, 16,32, or 640) that subjects experienced in a four-cue/two-task procedure to separate episodic and semantic memory retrieval components of the compound-stimulus strategy. Cue repetitions were faster than task repetitions, and task repetitions were only slightly faster than task alternations, suggesting that cue repetition effects account for the bulk of the difference between repetitions and alternations. We found the same effects with all target set sizes. The results are consistent with use of a semantic compound-stimulus strategy.

Tasks of a feather flock together: similarity effects in task switching.

Recent research on task switching has paid little attention to how tasks are represented and how the relations between task representations might affect the executive processes engaged to achieve a task switch. Two experiments investigated the effect of task similarity on task switching. Similarity was defined in terms of shared component operations--attentional control settings in Experiment 1 and response modality in Experiment 2--with tasks sharing more component operations said to be more similar to each other than tasks sharing fewer component operations. Across both experiments, task similarity facilitated task switching, seen in reduced switch costs for switching between similar tasks as opposed to dissimilar tasks. These results indicate that task similarity defined in terms of component operations can be used to define a multidimensional task space in which the executive processes of task selection and implementation are active.