The development of anticipatory cognitive control processes in task-switching: an ERP study in children, adolescents, and young adults

To investigate the development of advance task-set updating and reconfiguration, behavioral and event-related potential (ERP) data were recorded in children (9-10 years), adolescents (13-14 years), and young adults (20-27 years) in a cued task-switching paradigm. In pure blocks, the same task was repeated. In mixed blocks, comprised of stay and switch trials, two tasks were intermixed. Age differences were found for stay-pure performance (mixing costs) in the 600-ms but not in the 1200-ms cue-target interval (CTI). Children showed larger reaction time mixing costs than adults. The ERPs suggested that the larger costs were due to delayed anticipatory task-set updating in children. Switch-stay performance decrements (switch costs) were age-invariant in both CTIs. However, ERP data suggested that children reconfigured the task-set on some stay trials, rather than only on switch trials, suggesting the continued maturation of task-set reconfiguration processes.     

Electrophysiological correlates of anticipatory task-switching processes

Recent studies show a differential switch-related positivity emerging before a switch trial and reflecting anticipatory task-set reconfiguration processes. In this study, the switch-related positivity was examined in a cued task-switching paradigm. Cue-stimulus and response-stimulus intervals were independently manipulated to dissociate between the effects of anticipatory preparation and passive dissipation of task-set interference. Reaction time switch cost declined with increasing cue-stimulus and response-stimulus intervals, suggesting a contribution from both active preparation and passive interference processes. In cue-related difference waveforms, a switch positivity peaked around 350-400 ms and is interpreted as reflecting differential activation of task-set reconfiguration. In stimulus-related difference waveforms, a switch-related negativity is believed to indicate the role of S-R priming and response interference in task-switching.     

Switching, plasticity, and prediction in a saccadic task-switch paradigm

Several cognitive processes are involved in task-switching. Using a prosaccade/antisaccade paradigm, we manipulated both the interval available for preparation between the cue and the target and the predictability of trial sequences, to isolate the contributions of foreknowledge, an active switching (reconfiguration) process, and passive inhibitory effects persisting from the prior trial. We tested 15 subjects with both a random and a regularly alternating trial sequence. Half of the trials had a short cue–target interval of 200 ms, and half a longer cue–target interval of 2,000 ms. When there was only a short preparatory interval, switching increased the latencies for both prosaccades and antisaccades. With a long preparatory interval, switching was associated with a smaller latency increase for prosaccades and, importantly, a paradoxical reduction in latency for antisaccades. Foreknowledge of a predictable sequence did not allow subjects to reduce switch costs in the manner that a long preparatory cue–target interval did. In the trials with short preparatory intervals, the effects on latency attributable to active reconfiguration processes were similar for prosaccades and antisaccades. We propose a model in which the passive inhibitory effects that persist from the prior saccadic trial are due not to task-set inertia, in which one task-set inhibits the opposite task-set, but to inhibition of the saccadic response-system by the antisaccade task, to account for the paradoxical set-switch benefit for antisaccades at long cue–target intervals. Our findings regarding foreknowledge show that previous studies used to support task-set inertia may have conflated the effects of both active reconfiguration and passive inhibitory processes on latency. While our model of response-system plasticity can explain a number of effects of dominance asymmetry in switching, other models fail to account for the paradoxical set-switch benefit for antisaccades.     

Effects of caffeine on anticipatory control processes: evidence from a cued task-switch paradigm

Effects of caffeine on task switching were studied using ERPs in a cued task-switch paradigm. The need for advance preparation was manipulated by varying the number of task-set aspects that required switching. In a double-blind, within-subjects experiment, caffeine reduced shift costs compared to placebo. ERPs revealed a negative deflection developing within the preparatory interval, which was larger for shift than for repeat trials. Caffeine increased this shift-induced difference. Furthermore, shift costs increased as a function of the number of task-set features to be switched, but this pattern was not modulated by caffeine. The results suggest that caffeine improves task-switching performance by increasing general effects on task switching, related to task-nonspecific (rather than task-specific) anticipatory processes. Caffeine's actions may be mediated by dopaminergic changes in the striatum or anterior cingulate cortex.     

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.     

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.     

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.     

Mental fatigue and task control: planning and preparation

The effects of mental fatigue on planning and preparation for future actions were examined, using a task switching paradigm. Fatigue was induced by "time on task," with subjects performing a switch task continuously for 2 hr. Subjects had to alternate between tasks on every second trial, so that a new task set was required on every second trial. Manipulations of response-stimulus intervals (RSIs) were used to examine whether subjects prepared themselves for the task change. Behavioral measurements, event-related potentials (ERPs), and mood questionnaires were used to assess the effects of mental fatigue. Reaction times (RTs) were faster on trials in which no change in task set was required in comparison with switch trials, requiring a new task set. Long RSIs were used efficiently to prepare for the processing of subsequent stimuli. With increasing mental fatigue, preparation processes seemed to become less adequate and the number of errors increased. A clear poststimulus parietal negativity was observed on repetition trials, which reduced with time on task. This attention-related component was less pronounced in switch trials; instead, ERPs elicited in switch trials showed a clear frontal negativity. This negativity was also diminished by time on task. ERP differences between repetition and switch trials became smaller with increasing time on task.     

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.     

Pre-stimulus EEG effects related to response speed, task switching and upcoming response hand

The task-switching paradigm provides an opportunity to study whether oscillatory relations in neuronal activity are involved in switching between and maintaining task sets. The EEG of subjects performing an alternating runs [Rogers, R.D., Monsell, S., 1995. Costs of a predictable switch between simple cognitive tasks. Journal of Experimental Psychology: General 124, 207-231] task-switching task was analyzed using event-related potentials, the lateralized readiness potential, instantaneous amplitude and the phase-locking value [Lachaux, J.P., Rodriguez, E., Martinirie, J., Varela, F.J., 1999. Measuring phase synchrony in brain signals. Human Brain Mapping 8, 194-208]. The two tasks differed in the relevant modality (visual versus auditory) and the hand with which responses were to be given. The mixture model [de Jong, R., 2000. An intention driven account of residual switch costs. In: Monsell, S., Driver, J. (Eds.), Attention and Performance XVII: Cognitive Control. MIT Press, Cambridge] was used to assign pre-stimulus switch probabilities to switch trials based on reaction time; these probabilities were used to create a fast-slow distinction between trials on both switch and hold trials. Results showed both time- and time-frequency-domain effects, during the intervals preceding stimuli, of switching versus maintenance, response speed of the upcoming stimulus, and response hand. Of potential importance for task-switching theory were interactions between reaction time by switch-hold trial type that were found for a frontal slow negative potential and the lateralized readiness potential during the response-stimulus interval, indicating that effective preparation for switch trials involves different anticipatory activity than for hold trials. Theta-band oscillatory activity during the pre-stimulus period was found to be higher when subsequent reaction times were shorter, but this response speed effect did not interact with trial type. The response hand of the upcoming task was associated with lateralization of pre-stimulus mu- and beta-band amplitude and, specifically for switch trials, beta-band phase locking.     

Behavioural and electrophysiological measures of task switching during single and mixed-task conditions

In order to understand how the brain prepares for and executes a switch in task demand, we measured reaction time (RT), accuracy, and event-related brain potentials associated with performance in single and mixed-task blocks using a cued design. Our results show that trials which repeat in a mixed-task block (repeat trials) were more demanding than trials which repeated in a single-task block, as reflected by the presence of a RT mixing cost and by the presence of a smaller target-locked positivity (P3b) on repeat trials. Within a mixed-task block, repeat and switch trials also differed, where repeat trials showed evidence of greater preparation (larger cue-locked negativity), more efficient target processing (larger target-locked P3b), and shorter RTs. In addition, the cue-locked negativity difference remained despite equating repeat and switch trials on RT, suggesting that this negativity difference is specific to the switching process. Our results are discussed in light of existing models of task switching.     

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.     

Impaired semantic processing during task‐set switching: Evidence from the N400 in rapid serial visual presentation

The cognitive system is able to reconfigure mental resources flexibly to adapt to new a task. While task‐set switching is known to be detrimental to behavioral performance, less is known about the precise loci of these effects on stimulus processing. We measured event‐related potentials to explore the neural consequences of task‐set switching on semantic processing. We examined the context‐sensitive N400 component evoked by the second of two target words embedded in a rapid serial visual presentation under conditions that involved either a task‐set switch or no switching. Whereas the N400 was unaffected by the lag separating the targets in the absence of switching, it was delayed and attenuated in the switch condition when the targets were adjacent in the sequence. These findings indicate that task‐set reconfiguration temporarily prevents semantic activation and provide evidence for the nonautomaticity of semantic processing of words.     

Task-switching in schizophrenia: active switching costs and passive carry-over effects in an antisaccade paradigm

It has been hypothesized that impaired task-switching underlies some of the behavioural deficits in schizophrenia. However, task-switching involves many cognitive operations. In this study our goal was to isolate the effects on latency and accuracy that can be attributed to specific task-switch processes, by studying the inter-trial effects in blocks of randomly mixed prosaccades and antisaccades. By varying the preparatory interval between an instructional cue and the target, we assessed the costs of both (1) an active reconfiguration process that was triggered by the cue, and (2) passive carry-over effects persisting from the prior trial. We tested 15 schizophrenic subjects and 14 matched controls. A very short preparatory interval increased error rates and saccadic latencies in both groups, but more so in schizophrenia, suggesting difficulty in rapidly activating saccadic goals. However, the contrast between repeated and switched trials showed that the costs of task switching in schizophrenia were not significantly different from the controls, at either short or long preparatory intervals, for both antisaccades and prosaccades. These results confirm prior observations that passive carry-over effects are normal in schizophrenia, and show that active reconfiguration is also normal in this disorder. Thus problems with executive control in schizophrenia may not affect specific task-switching operations.     

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.     

Impaired preparatory re-mapping of stimulus-response associations and rule-implementation in schizophrenic patients--the role for differences in early processing

An accurate representation of task-set information is needed for successful goal directed behavior. Recent studies point to disturbances in the early processing stages as plausible causes for task-switching deficits in schizophrenia. A task-cueing protocol was administered to a group of schizophrenic patients and compared with a sample of age-matched healthy controls. Patients responded slower and less accurate compared with controls in all conditions. The concurrent recording of event-related brain potentials to contextual cues and target events revealed abnormalities in the early processing of both cue-locked and target-locked N1 potentials. Abnormally enhanced target-locked P2 amplitudes were observed in schizophrenic patients for task-switch trials only, suggesting disrupted stimulus evaluation and memory retrieval processes. The endogenous P3 potentials discriminated between task conditions but without further differences between groups. These results suggest that the observed impairments in task-switching behavior were not specifically related to anticipatory set-shifting, but derived from a deficit in the implementation of task-set representations at target onset in the presence of irrelevant and conflicting information.     

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.     

Bursts of occipital theta and alpha amplitude preceding alternation and repetition trials in a task-switching experiment

The instantaneous amplitude of the theta and alpha bands of the electroencephalogram (EEG) was studied during preparation periods in a task-switching experiment. Subjects had to switch between tasks in which they were to respond to either the visual or the auditory component of the stimulus. 11-13 Hz occipital amplitude increased prior to auditory, relative to visual repetition trials. The effect was transient, ending well before presentation of the stimulus that was being prepared for. Alternation trials were preceded by an increase in occipital theta-band activity, relative to repetition trials, for the visual task. This effect was also transient. The effects suggest tentative hypotheses for the function of transient bursts of alpha- and theta-band oscillations and indicate the possibility of a psychophysiological resolution of theoretical questions concerning the origin of switch costs.     

Cortical activation associated with midtrial change of instruction in a saccade task

The appearance of a visual stimulus in the peripheral visual field can elicit different saccade responses depending on prior instruction. This flexibility is commonly attributed to differences in motor set. Little is known about how the brain switches between one saccade response and another. To investigate the neural processes associated with switches between saccade motor sets, we recorded event-related potentials (ERPs) in 13 subjects, in three tasks that required subjects to generate prosaccades to a visual stimulus on 75% of the trials. On 25% of the trials, the color of the fixation point (FP) changed 300 ms prior to stimulus presentation. In the "ANTI" task, the change of the FP was the instruction to generate an antisaccade; in the "NOGO" task, subjects were instructed to maintain fixation; and in the "PRO" task, subjects were instructed to generate a prosaccade. The switch in motor set from prosaccades to antisaccades in the ANTI task and the cancellation of the prosaccade motor set in the NOGO task modulated frontal and frontocentral channels. Futhermore, the ANTI task but not the NOGO task was associated with differences at central and parietal channels compared with the PRO task. We hypothesize that the frontal activation in the ANTI and NOGO task reflects inhibition and task-switching processes, whereas the parietal activation reflects the preparation of this area for the sensorimotor transformation process that is necessary for the generation of an antisaccade.     

Age differences in attentional control: an event-related potential approach

We examined age differences in event-related potentials (ERPs) associated with attentional control of task-set selection and response interference by means of a cue-based switching paradigm in which participants performed the color or word Stroop task. The results of ERPs in the cue interval indicated that P3 latencies were slowed for older adults, suggesting age-related slowing in updating currently relevant task sets. Older adults also showed a larger CNV under switching than nonswitching conditions, indicating age differences in maintaining task sets over longer periods of time. The results of target-locked ERPs revealed a negativity to incompatible Stroop trials (Ni) that was prolonged for older adults, suggesting age differences in early conflict processing. Response-locked ERPs showed a negative deflection to incompatible Stroop trials (CRN) only for younger adults, suggesting age differences also in response-related conflict processing.