Cue-independent task-specific representations in task switching: evidence from backward inhibition

The compound-cue model of cognitive control in task switching explains switch cost in terms of a switch of task cues rather than of a switch of tasks. The present study asked whether the model generalizes to Lag 2 repetition cost (also known as backward inhibition), a related effect in which the switch from B to A in ABA task sequences is costlier than is the same switch in CBA task sequences. The model suggests that Lag 2 repetition cost should be absent from A'BA task sequences, in which A' and A are different cues for the same task. The cost is robust on such sequences, which suggests that cue-independent, task-specific representations are necessary for explaining task-switching performance and that the compound-cue model has limited explanatory power.     

Space-time compatibility effects in the auditory modality

Previous research suggests that past and future temporal concepts are spatially represented from left to right along a mental line. And these concepts can both prime motor responses to left or right space and direct visual spatial attention. The present study aimed at investigating the nature of this space-time conceptual metaphor in different auditory tasks. In the first experiment, subjects categorized time-related words (past or future) that were presented binaurally. In the second experiment, subjects detected left-ear or right-ear targets following time-related words. The similar space-time compatibility effects were found in these two experiments. Our results demonstrate that the activation of temporal concepts can both prime motor responses to left or right space and influence the orientation of auditory spatial attention, suggesting that the modality of the stimulus input is unimportant for the left-right mapping of time. These results are explained by the "intermediate coding" account.     

Instruction effects in task switching

The present study examined the effect of instructions on sequential task preparation using a cuing paradigm with three tasks. All task transitions were predictable, whereas task identity was unpredictable in switches but predictable in repetitions. In Experiment 1, predictability (predictable vs. random) was manipulated while preparation time (i.e., the cue-stimulus interval, or CSI) remained constantly short. In Experiment 2, CSI was manipulated for predictable task transitions. Both experiments showed clear instruction effects, but these were restricted to predictable task repetitions, for which predictability determined the identity of the upcoming task. Predictability effects were small in task switches and were not modulated by instruction, suggesting that preparation is mainly task-specific rather than switch-specific. Together, these results suggest that intentional processes contribute to predictability benefits in task repetitions, probably by enhancing the monitoring of sequential transitions in working memory in order to maintain activation in task repetitions.     

On the representation of task information in task switching: Evidence from task and dimension switching

Task switching research has revealed that task changes lead to a performance switch cost. The present study focuses on the organization of task components in the task set. Three different views of task set organization have been distinguished and evidence in favor of each of these has been reported in the literature. In four experiments, we orthogonally varied the categorization task (magnitude and parity) and the stimulus dimension on which the categorization was to be made. Experiments 1, 2, and 4 used Stroop-like number stimuli, whereas Experiment 3 used global-local stimuli to define the stimulus dimension. In Experiments 2-4, the cue-stimulus interval was also varied. The findings showed that a change of any component resulted in a cost, without any reliable difference in the size of these costs. These results are consistent with the flat view on task-set organization, which assumes that the task set binds all elements in an unstructured representation, which is completely reconfigured each time a change to the task set is required. The implications of these findings are discussed in relation to other findings and the different views on task-set organization.     

Constrained motor-perceptual task in infancy: effects of sensory modality

The authors examined the relative success of varying sensory stimulation modalities that they presented via a mobile reinforcement procedure for promoting left-knee extensions in 3-month-old infants. They separated 53 infants into 5 groups. Four groups received contingent unimodal auditory, enhanced auditory, or visual reinforcement or contingent bimodal auditory plus visual (aud + vis) reinforcement. One group (controls) received aud + vis noncontingent reinforcement. The group that received aud + vis contingent reinforcement was most successful in learning the motor task and maintained the highest attention levels. The authors observed few differences in learning and attention within the unimodal groups. The present findings confirm the effectiveness of contingent multisensory stimulation for promoting perception-action coupling in infancy.     

Response selection and response execution in task switching: evidence from a go-signal paradigm

The present study used a go/no-go signal delay (GSD) to explore the role of response-related processes in task switching. A go/no-go signal was presented at either 100 ms or 1,500 ms after the stimulus. Participants were encouraged to use the GSD for response selection and preparation. The data indicate that the opportunity to select and prepare a response (i.e., long GSD) resulted in a substantial reduction of task-shift costs (Experiment 1) and n-2 task-repetition costs (i.e., backward inhibition; Experiment 2) in the current trial. These results suggest that interference from the preceding trial can be resolved during response selection and preparation. Furthermore, the shift costs and the n-2 repetition costs after no-go trials with long GSD (i.e., response selection but no execution) were markedly smaller than after go trials. These findings suggest that the interference that gives rise to shift costs and n-2 repetition costs is related not solely to response selection but also to response execution. Thus, the present study demonstrates dissociable contributions of response selection and response execution to interference effects in task switching.     

Working memory and the control of action: evidence from task switching.

A series of 7 experiments used dual-task methodology to investigate the role of working memory in the operation of a simple action-control plan or program involving regular switching between addition and subtraction. Lists requiring switching were slower than blocked lists and showed 2 concurrent task effects. Demanding executive tasks impaired performance on both blocked and switched lists, whereas articulatory suppression impaired principally the switched condition. Implications for models of task switching and working memory and for the Vygotskian concept of verbal control of action are discussed.     

Inner speech sustains predictable task switching: direct evidence in adults

It has been proposed that inner speech supports task selection in task-switching studies, especially when the need for endogenous control is increased. This has been established through the suppression of inner speech in cognitive-flexibility tasks that leads to poorer performance. The aim of this study is to quantify the role of inner speech in a flexibility task by using surface laryngeal electromyography, which, contrary to previous studies, enables participants to freely verbalise the tasks. We manipulated endogenous and exogenous flexibility in a mathematical switching task paradigm. Experiment 1 shows that inner speech acts as a support for switching and is recruited more often when the tasks are of an endogenous type. The main result of Experiment 2 that language is recruited more for the mixing cost than for the switch cost (regardless of the endogenous factor) extends past findings obtained through articulatory suppression.     

Training and transfer effects in task switching

Performance on task switching, a paradigm commonly used to measure executive function, has been shown to improve with practice. However, no study has tested whether these benefits are specific to the tasks learned or are transferable to new situations. We report evidence of transferable improvement in a cued, randomly switching paradigm as measured by mixing cost, but we report no consistent improvement for switch cost. Improvement in mixing costs arises from a relative reduction in time to perform both switch and nonswitch trials that immediately follow switch trials, implicating the ability to recover from unexpected switches as the source of improvement. These results add to a growing number of studies demonstrating generalizable improvement with training on executive processing.     

The effects of recent practice on task switching

Four experiments investigated the effect of recent selective practice on the cost of switching between 2 tasks afforded by letter-digit pairs: alphabet arithmetic and shape comparison. Experiments 1 and 2 found a greater cost associated with switching to the more recently practiced task: evidence that task-set inertia contributes to switching costs. Experiment 3 found this effect to be limited to trials on which a recently trained stimulus followed another such stimulus: a result problematic for all current theories of task-set priming. Experiment 4 showed that the effect of recent practice was eliminated by active preparation for a task switch: It appears that endogenous task-set preparation reduces the effects of task-set inertia. ((c) 2003 APA, all rights reserved)     

Probe-specific proportion task repetition effects on switching costs

In two experiments, participants were presented with successive presentations of animal names (e.g., GORILLA, WHALE)--a prime display followed by a probe display. In response to each display, participants judged either the typical habitat or the relative size of those animals, repeating the same task in response to both displays on half of the experimental trials and switching from one task to the other on the other half of trials. Our results demonstrate that switch costs can be reduced when either the probe's identity or its location is predictive of a change in task. This result establishes that the presentation of a stimulus can serve as a rapid cue for facilitating a switch in task, independent of processes occurring both at the time of the prime task and during the intervening period between the prime and probe tasks. We discuss the implications of these results for prevailing explanations of task switching costs.     

Effects of anxiety on task switching: Evidence from the mixed antisaccade task

According to the attentional control theory of anxiety (Eysenck, Derakshan, Santos, & Calvo, 2007), anxiety impairs performance on cognitive tasks that involve the shifting function of working memory. This hypothesis was tested using a mixed antisaccade paradigm, in which participants performed single-task and mixed-task versions of the paradigm. The single task involved the completion of separate blocks of anti- and prosaccade trials, whereas in the mixed task, participants completed anti- and prosaccade trials in a random order within blocks. Analysis of switch costs showed that high-anxious individuals did not exhibit the commonly reported paradoxical improvement in saccade latency, whereas low-anxious individuals did. The findings are discussed within the framework of attentional control theory.     

Effects of stimulus features and instruction on response coding, selection, and inhibition: evidence from repetition effects under task switching

The coding of stimuli and responses is crucial for human behaviour. Here, we focused primarily on the response codes (or response categories). As a method, we applied a combined dual-task and task-switch paradigm with a fixed task-to-hand mapping. Usually, negative effects (i.e., costs) are observed for response category repetitions under task switching. However, in several previous studies it has been proposed that such repetition effects do not occur, if the stimulus categories (e.g., "odd" if digits have to be classified according to their parity feature) are unequivocally mapped to specific responses. Our aim was to test this hypothesis. In the present experiments, we were able to distinguish between three different types of possible response codes. The results show that the participants generally code their responses according to abstract response features (left/right, or index/middle finger). Moreover, the spatial codes were preferred over the finger-type codes even if the instructions stressed the latter. This preference, though, seemed to result from a stimulus-response feature overlap, so that the spatial response categories were primed by the respective stimulus features. If there was no such overlap, the instructions determined which type of response code was involved in response selection and inhibition.     

Spatial S-R compatibility effects in an intentional imitation task

The active intermodal mapping hypothesis suggests that intentional imitation is mediated by a highly efficient, special-purpose mechanism of actor-centered movement encoding. In the present study, using methods from stimulus-response (S-R) compatibility research, we found no evidence to support this hypothesis. In two experiments, the performance of adult participants instructed to imitate actorcentered spatial properties of head, arm, and leg movements was affected by task-irrelevant, egocentric spatial cues. In Experiment 1, participants imitated using the same side of their bodies as did the model, and performance was less accurate when egocentric stimulus location was response incompatible than when it was response compatible. This effect was reversed in Experiment 2 when participants imitated using the opposite side of their bodies. These findings, in line with general process theories of imitation, imply that intentional imitation is mediated by the same processes that mediate responding to inanimate stimuli on the basis of arbitrary S-R mappings.     

Modeling graded response congruency effects in task switching

Compound cue retrieval is a computational model of a mediated route for response selection in task-switching situations. In previous studies, the model has been shown to account for response congruency effects when switching between two tasks, where response congruency reflects the degree of match between relevant and irrelevant task responses associated with a target stimulus. In the present study, the author derived a model prediction of graded response congruency effects in situations involving three tasks. The predicted pattern was observed for both response time and error rate in an experiment in which numerical categorization tasks were performed on single-digit targets. Implications for understanding response congruency effects and for developing models of task-switching performance are discussed.     

Cognitive control in number processing: new evidence from number compatibility effects in task-switching

Cognitive Processing - A growing body of research suggests that basic numerical abilities such as number magnitude processing are influenced by cognitive control processes. So far, evidence for...     

Differential effects of aging on processes underlying task switching

In this study, we used event-related brain potentials (ERPs) to examine the effects of aging on processes underlying task switching. The response time data revealed an age-related increase in mixing costs before controlling for general slowing and no effect of aging on switching costs. In the cue-locked epoch, the ERP data revealed little effect of age on the parietal P3 related to cue encoding, an age-related decrease in parietal activity related to cue retrieval, and an age-related increase in the amplitude of the parietal and frontal activity related to task set configuration and rule mapping. In the target-locked epoch, there was differential neural recruitment in younger and older adults in response to task mixing. These data are consistent with the idea that older adults may not fully implement task set before onset of the target stimulus.     

Aging, focus switching, and task switching in a continuous calculation task: evidence toward a new working memory control process

This study examined switching of the focus of attention in working memory in relation to global task switching in a continuous calculation task using two rules (midpoint and up-and-down) in a group of 25 younger adults and a group of 23 older adults. Age differences emerged in accuracy when participants worked on two strings simultaneously (necessitating a focus switch); focus switching did not interact with age in the response time domain. No age differences were obtained for global task switching. Ex-Gaussian decomposition showed a shift due to focus switching in all parameters, but a shift in leading edge only for task switching. The results suggest that task switching and focus switching rely on different processes, and that there is a specific age-related deficit in focus switching.     

Task switching in a hierarchical task structure: evidence for the fragility of the task repetition benefit

This study examined how task switching is affected by hierarchical task organization. Traditional task-switching studies, which use a constant temporal and spatial distance between each task element (defined as a stimulus requiring a response), promote a flat task structure. Using this approach, Experiment 1 revealed a large switch cost of 238 ms. In Experiments 2-5, adjacent task elements were grouped temporally and/or spatially (forming an ensemble) to create a hierarchical task organization. Results indicate that the effect of switching at the ensemble level dominated the effect of switching at the element level. Experiments 6 and 7, using an ensemble of 3 task elements, revealed that the element-level switch cost was virtually absent between ensembles but was large within an ensemble. The authors conclude that the element-level task repetition benefit is fragile and can be eliminated in a hierarchical task organization.