A carry-over task rule in task switching: An ERP investigation using a Go/Nogo paradigm

Investigations of executive control using a task-switching paradigm have consistently found longer reaction times for task-switch trials than task-repetition trials. This switch cost may result from interference by a stimulus-response (SR) rule carried over from the preceding alternative task. We examined event-related brain potential (ERP) evidence for such carry-over effects using a combined paradigm of task switching with Go/Nogo; Nogo trials, which require no response execution, should expose carry-over effects from preceding trials. On Go trials, twelve participants performed a button-pressing task in compatible (hand and signal direction consistent) and incompatible conditions, which switched predictably every three trials. Reaction times were longer on switch than on repetition trials. On compatible switch trials, a stimulus-locked lateralized readiness potential (sLRP) for Nogo stimuli revealed a positive dip, suggesting incorrect response activation in the early automatic process that was induced by a SR rule carried over from the preceding task.     

The effect of task preparation in task switching as reflected on lateralized readiness potential.

The present study examined whether task preparation had an equivalent beneficial effect for both switch and repeat trials in the context of a task switching paradigm. A pair-wise task-switching paradigm was used where each trial was comprised of two tasks that were either the same (task repeat) or different (task switch). The effect of preparation was manipulated so that participants either performed pure repeat trials or pure switch trials in separate blocks (foreknowledge conditions) or performed both switch and repeat trials within the same block (non-foreknowledge conditions). In addition, the time interval between the response to the first task and the onset of the next task's stimulus (response-stimulus interval, RSI) was set at either 300 ms or 600 ms. Both stimulus-locked and response-locked lateralized readiness potentials were measured to examine at what stage in time that task preparation affects the task performance. The results showed that task preparation had the same amount of beneficial effect on the stage of response selection for both switch and repeat trials, regardless of whether the RSI was short or long.     

Task set switching in schizophrenia

The authors used a task-switching paradigm to investigate set shifting ability in schizophrenia. This paradigm included 2 choice reaction time (RT) tasks: up-down and right-left. Switching tasks were associated with costs (i.e., longer RT in task-switch trials than in task-repetition trials); patients responded more slowly than controls and suffered greater switching costs, were as efficient as controls in engaging in an upcoming task set, and were faster than controls in disengaging from the previous task set. There were indications that patients quickly forgot what each keypress indicated, making it necessary for them to acquire response meaning information anew in each trial. To test this notion, the authors subsequently tested normal participants in conditions in which response meaning information needed to be acquired anew in each trial. These participants produced a pattern of switching costs resembling that of patients. Results suggest that set switching difficulties in schizophrenia, as exhibited in the present paradigm, reflect poor memory for task context information.     

The lateralized readiness potential and P300 of stimulus-set switching

The present study aimed at investigating whether stimulus-set switching involves the same stages of information processing as response-set switching. A pair-wise task switching paradigm in which the trial sequences comprised only two tasks was used. The effect of preparation was manipulated so that the participants performed only the repeat trials in some blocks and only the switch trials in other blocks, or both the repeat and switch trials were randomly mixed within a single block. P300 peak latency and stimulus- and response-locked lateralized readiness potential intervals were used to indicate the processing stage of stimulus identification, response selection and motor execution, respectively. The results demonstrated that the stimulus-set switching involves stages of information processing following stimulus identification and before motor execution.     

Sequence effects in cued task switching modulate response preparedness and repetition priming processes

In task‐switching paradigms, reaction time (RT) switch cost is eliminated on trials after a no‐go trial (no‐go/go sequence effect). We examined the locus of no‐go interference on task‐switching performance by comparing the event‐related potential (ERP) time course of go/go and no‐go/go sequences from cue onset to response execution. We also examined whether noninformative trials (i.e., delayed reconfiguration, no response inhibition) produce similar sequence effects. Participants switched using informative and noninformative cues ( Experiment 2 ) intermixed with no‐go trials ( Experiment 1 ). Repeat RT was slower for both no‐go/informative (pNG/I) and noninformative/informative (pNI/I) than informative/informative sequences. ERPs linked to anticipatory preparation showed no effect of trial sequence. ERPs indicated that pNG/I sequences reduce response readiness whereas pNI/I sequences reduce repetition benefit for repeat trials. Implications for task‐switching models are discussed.     

Brain oscillatory activity associated with switch and mixing costs during reactive control

Task-switching paradigms, which involve task repetitions and between-task switches, have long been used as a benchmark of cognitive control processes. When mixed and single-task blocks are presented, two types of costs usually occur: the switch cost, measured by contrasting performance on switch and repeat trials during the mixed-task blocks, and the mixing cost, calculated as the performance difference between the all-repeat trials from the single-task blocks and the repeat trials from the mixed-task blocks. Both costs can be mitigated by informational cues that signal the upcoming task switch beforehand. Recent electroencephalographic studies have started unveiling the brain oscillatory activity underlying the switch cost during the preparatory cue-target interval, thus, targeting proactive control processes. Less attention has instead been paid to the mixing cost and, importantly, to the oscillatory dynamics involved in switch and mixing costs during reactive control. To fill this gap, here, we analyzed the time-frequency data obtained during a task-switching paradigm wherein the simultaneous presentation of task cues and targets increased the need for reactive control. Results showed that while alpha and beta bands were modulated by switch and mixing costs in a similar gradual fashion, with greater suppression going from switch to repeat and all-repeat trials, theta power was sensitive to the switch cost with increased power for switch than repeat trials. Together, our findings join previous studies underlining the importance of theta, alpha and beta oscillations in task-switching and extend them by depicting the oscillations involved in switch and mixing costs during reactive control processes.     

Age differences in task switching and response monitoring: evidence from ERPs

This study investigates age differences in the flexible adaptation to changing demands on task switching and conflict processing. We applied a cued task-switching version of the Stroop task and manipulated the ratio of conflict trials. During task preparation, the P300 varied as a function of conflict ratio and a later positive component was larger for switch than non-switch trials. Stimulus-related conflict processing as indicated by a negativity for incompatible trials (Ni) was delayed for older adults. Moreover, the Ni varied as a function of conflict ratio and was larger for switch than for non-switch trials. Age differences were also obtained in the correct response negativity (CRN). CRN was larger on incompatible trials and this CRN-compatibility effect was enhanced when incompatible trials were infrequent in younger, but not in older adults. Our findings suggest impairments of older adults primarily in response-related conflict processing and in the flexible adaptation to changing task contexts.     

A new account of the effect of probability on task switching: ERP evidence following the manipulation of switch probability, cue informativeness and predictability

This task-switching ERP study of 16 young participants investigated whether increased RT slowing on stay trials and faster RTs on switch trials for frequent than infrequent switching are explained by an activation or preparation account. The activation account proposes that task sets are maintained at a higher baseline activation level for frequent switching, necessitating increased task-set updating, as reflected by a larger and/or longer lasting early parietal positivity. The preparation account assumes advance (pre-cue) switch preparation (i.e., task-set reconfiguration), preceding stay and switch trials for frequent switching, as reflected by pre-cue and post-cue late parietal positivities. By and large, the data support the activation account. However, we also found increased, pre-cue task-set updating on frequent stay trials and pre-cue, task-set reconfiguration prior to predictable, frequent switches. These results lead us to propose an extended activation account to explain the effects of switch probability on the executive processes underlying task-switching behavior.     

Age-related differences in the timing of stimulus and response processes during visual selective attention: Performance and psychophysiological analyses

In this study, age-related differences in the selection of visual information were investigated. Two groups of younger and older subjects performed focused- and divided-attention (i.e., visual search) tasks. In the focused-attention task, centrally presented target letters could be flanked by compatible or incompatible noise letters. In the visual search task, targets could be cued or uncued, and target locations could be spatially compatible or incompatible with the responding hand. P3 latency, lateralized readiness potentials, the electromyogram, and reaction times were used to detect possible age-related differences in the timing of stimulus- and response-related processes during selective processing of information. In the focused-attention task, performance of older subjects showed greater interference by incompatible flankers than did that of younger subjects because of stronger response competition caused by partial activation of the incorrect response channel by the incompatible flankers. No evidence was found of specific age-related differences in the efficiency of visual search in a divided-attention task. Furthermore, in both tasks, younger subjects showed an earlier start of response execution (in the electromyogram) relative to the onset of response preparation (lateralized readiness potential) and a higher percentage of incorrect electromyographic activity than did older subjects.     

Cue- versus response-locked processes in backward inhibition: evidence from ERPs

A task set may need to be inhibited to facilitate the switch to another task. This event-related potential (ERP) study determined (1) whether backward inhibition (BI) is exerted preferentially in high interference environments, and (2) whether ERPs locked to critical time points reflect BI during cue preparation and/or response stages. High interference (HI) and low interference (LI) were created by manipulating task difficulty. A reaction time (RT) BI effect (i.e., BI>control trials) was shown only during HI tasks. Cue-locked ERPs on LI tasks suggest increased attentional resources were allocated during the reactivation of a recently inhibited task. For HI tasks, BI versus control trial differences were reflected in a response-locked ERP negativity only after response selection (indexed by the response-locked lateralized readiness potential), indicating that BI is a lateral inhibition mechanism exerted during response preparation.     

The influence of rTMS over the right dorsolateral prefrontal cortex on intentional set switching

High frequency (HF) repetitive transcranial magnetic stimulation (rTMS) has an excitatory effect on neurons of a specific brain area. The dorsolateral prefrontal cortex (DLPFC) has been associated with executive functions, such as task set switching. One important experimental paradigm for investigating such higher order cognitive control is the task-switching (TS) paradigm. A TS paradigm requires switching between two conditional response tasks with mutually incompatible response–selection rules. In the present study, the influence of HF rTMS over the right DLPFC in healthy female volunteers on a modified TS paradigm was investigated. As expected, reaction time on cued switching trials decreased significant after rTMS, as compared to non-cued switch trials. No changes emerged after the placebo sham condition. Mood remained unchanged after rTMS. These findings demonstrate the role of the right DLPFC in cued intentional set switch initiation.     

Bimanual coordination affects motor task switching

Task-switching paradigms have generally been used to investigate cognitive processes involved in decision making or allocating attention. This work extended the task-switching paradigm into the motor domain in order to investigate the consequences of an unexpected environmental perturbation on reaction time and movement time. Typically, task-switching paradigms have investigated consequences of rearranging task sets from one trial to the next; this work explored rearranging planned movements within the context of a single trial. Of particular interest was how the motor system reorganizes coordination patterns when reaching amplitude congruency is manipulated between the two hands. Results for Experiment 1 and the far distance in Experiment 2 indicated that reaction time switch costs were the smallest during congruent task-switch trials, where reaching amplitudes between the two hands were the same. This implies that a planned movement parameter for one hand is accessible for the other hand in the circumstance of an unexpected task switch. However, the reversed congruency effects found for the near distance in Experiment 2 suggest that the ability to capitalize on stored parameter information to decrease reaction time is dependent on environmental factors and task instructions. Movement time results showed that even if a movement with one hand is aborted in mid-execution, it can still influence the performance of the other hand during a task switch. This suggests that bimanual coordination can affect prehensile performance even though only one hand has a goal to achieve.     

Caffeine improves anticipatory processes in task switching

We studied the effects of moderate amounts of caffeine on task switching and task maintenance using mixed-task (AABB) blocks, in which participants alternated predictably between two tasks, and single-task (AAAA, BBBB) blocks. Switch costs refer to longer reaction times (RT) on task switch trials (e.g. AB) compared to task-repeat trials (e.g. BB); mixing costs refer to longer RTs in task-repeat trials compared to single-task trials. In a double-blind, within-subjects experiment, two caffeine doses (3 and 5mg/kg body weight) and a placebo were administered to 18 coffee drinkers. Both caffeine doses reduced switch costs compared to placebo. Event-related brain potentials revealed a negative deflection developing within the preparatory interval, which was larger for switch than for repeat trials. Caffeine increased this switch-related difference. These results suggest that coffee consumption improves task-switching performance by enhancing anticipatory processing such as task set updating, presumably through the neurochemical effects of caffeine on the dopamine system.     

Asymmetric switch cost: an investigation using lateralized readiness potentials

Switching to a dominant task incurs larger costs than switching to a non-dominant task. This study investigated whether this cost asymmetry derives from the inhibition of the dominant task rule that occurred during the previous trial. Participants were presented with a five-letter array consisting of (left) and (right), and asked to respond to the central target letter after being informed about the task rule with a pre-cue. The rule was switched between dominant (left-hand to, right-hand to) and non-dominant tasks (right-hand to, left-hand to) every two trials. Reaction times revealed the asymmetrical switch cost and the effect of target-flanker congruency. Stimulus-locked lateralized readiness potentials showed that the dominant task rule was inhibited during the non-dominant task, whereas this inhibition was not carried over to the dominant task trial.     

On the automaticity of ipsilateral response activation in the Simon effect

The effects on performance of unattended stimulus–response spatial relationships in choice reaction time tasks (i.e., the Simon effect) have been attributed to automatic activation of the response ipsilateral to stimulus location. We tested this assumption using the lateralized readiness potential (LRP). The response key labels changed randomly from trial to trial and were presented either 400 ms before (immediate-reaction trials) or 400 ms after (delayed-reaction trials) stimulus. The critical test for the automatic activation hypothesis was on delayed-reaction trials, in which LRP deflections were expected in the interval between stimulus and response-key labels. Contrary to this prediction, there were no LRP signs of response activation within that interval.     

Electrophysiological correlates of anticipatory and poststimulus components of task switching

Task-switching paradigms can shed light on cognitive and neural processes underlying attentional control mechanisms. An alternating runs task-switching paradigm (R. D. Rogers & S. Monsell, 1995) is used to identify ERP components associated with anticipatory and poststimulus components of task-switching processes. Subjects alternated between two tasks in a predictable series (AABB). Reaction time (RT) switch cost reduced with increasing response-stimulus (R-S) interval and a residual switch cost remained at the longest R-S interval. A switch-related positivity (D-Pos) developed in the R-S interval. D-Pos was time-locked to response onset, peaked around 400 ms post-response onset, and was unaffected by task-set interference. A switch-related negativity (D-Neg) emerged after stimulus onset. D-Neg peaked earlier with increasing R-S interval and its amplitude and latency were affected by task-set interference. D-Pos and D-Neg were interpreted within current models of task-switching.     

Effects of switching between leftward and rightward pro- and antisaccades

Previous studies suggested that random switching between pro- and antisaccades increases errors in both tasks. However, little is known about the effects of switching between leftward and rightward saccades (response switching). The present study investigated task and response switching using an alternating runs procedure. Tasks (i.e., prosaccades versus antisaccades) were switched every second trial. Response switches (i.e., leftward saccades versus rightward saccades) were counterbalanced across tasks and task-switching conditions. Task switching increased errors in both tasks. Response switching increased errors when antisaccades were preceded by antisaccades but not when antisaccades were preceded by prosaccades or for prosaccades regardless of the preceding saccade type. The task-switch effects suggest that both pro- and antisaccade trials activate specific production rules that can persist in a subsequent trial. The differential response-switch effects may reflect different modes of response activation in pro- and antisaccades (sensorimotor transformation of visual information versus selection of motor programs).     

Anticipatory cortico-cortical interactions: switching the task configuration between effectors

Cognitive regulation enables a subject to plan actions according to context and to respond in a flexible manner to environmental conditions. This implies that foreknowledge about a change in system configuration will trigger preparatory activity in anticipation of the impending transformation. In the present study, we evaluate a unimanual task under two performance conditions that affected the cognitive context, and examine modulations in cortico-cortical interactions as determined by EEG coherence. The right hand movement was performed in an experimental paradigm that necessitated in some trials a voluntary and predictable switch towards a left hand movement, whereas in other trials no switch was required and movement of the right hand continued. The data showed that execution of the right hand movement was associated with an increased degree of task-related coherence in the alpha frequency band (8–12 Hz) in the switching as compared to the no switching condition, and this was most apparent for fronto-parietal connections of the movement-driving (left) as well as for the primed (right) hemisphere. For the primed hemisphere, we observed that the information flow was driven from the F4 electrode overlying the prefrontal area, which suggests that anticipatory preplanning occurred. These data indicate that higher-order cognitive operations bias cortico-cortical interactions in respect of an upcoming switch of the task settings between effectors by recruiting neural resources proactively. Dynamic adjustments in the alpha band suggest that low frequency activity is a characteristic of distributed information processing related to movement planning.     

The effect of 40 h constant wakefulness on task-switching efficiency

This study investigated efficiency of switching between different tasks in 12 male participants (19–30 years) during 40 h of constant wakefulness. As index of task-switching efficiency, switch costs in reaction time were assessed every 3 h under controlled behavioural and environmental conditions. Overall reaction times and switch costs showed a temporal pattern consistent with the assumption of a combined influence of a sleep homeostatic and a circadian process. An additional analysis indicated that the variation in switch costs could not be attributed to interference of the current task with persisting activation from preceding tasks. We therefore conclude that sleep loss and the circadian system affect the ability to prepare the current task rather than automatic processing of irrelevant stimulus information.     

Event-related potential correlates of task switching and switch costs

Studies of task switching demonstrate that task switches are associated with response costs and that these costs are reduced when a cue is presented in advance of a switch. The present study examined cortical event-related potential correlates of task switching and switch costs in 39 participants during a cued match/mismatch discrimination task. Compared with non-switch trials, switch trials were associated with a larger cue-related, anticipatory P3b-like waveform. Switch trials were also associated with smaller target-related, stimulus-dependent P2 and P3-like components. Moreover, the switch-related amplitude variability in the P3b to the cue and the P2 to the target were associated with unique components of the residual switch costs. The results support an integrated model of task switching with complementary yet distinct roles for anticipatory and stimulus-dependent processes in task switching and switch costs.