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.     

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.     

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.     

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.     

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.     

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.     

Brief Reports: Anticipating the consequences of action: An fMRI study of intention‐based task preparation

A key component of task preparation may be to anticipate the consequences of task‐appropriate actions. This task switching study examined whether such type of “intentional” preparatory control relies on the presentation of explicit action effects. Preparatory BOLD activation in a condition with task‐specific motion effect feedback was compared to identical task conditions with accuracy feedback only. Switch‐related activation was found selectively in the effect feedback condition in the middle mid‐frontal gyrus and in the anterior intraparietal sulcus. Consistent with research on attentional control, the posterior superior parietal lobule exhibited switch‐related preparatory activation irrespective of feedback type. To conclude, preparatory control can occur via complementary attentional and intentional neural mechanisms depending on whether meaningful task‐specific action effects lead to the formation of explicit effect representations.     

Switch‐specific and general preparation map onto different ERP components in a task‐switching paradigm

We examined whether the cue‐locked centroparietal positivity is associated with switch‐specific or general preparation processes. If this positivity (300–400 ms) indexes switch‐specific preparation, faster switch trials associated with smaller RT switch cost should have a larger positivity as compared to slower switch trials, but no such association should be evident for repeat trials. We extracted ERP waveforms corresponding to semi‐deciles of each participant's RT distribution (i.e., fastest to slowest 5% of trials) for switch and repeat conditions. Consistent with a switch‐specific preparation process, centroparietal positivity amplitude was linked to slower RT and larger RT switch cost for switch but not repeat trials. A later pre‐target negativity (500–600 ms) was inversely correlated with RT for both switch and repeat trials, consistent with a general anticipatory preparation processes.     

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.     

Effects of aging and job demands on cognitive flexibility assessed by task switching

In a cross-sectional, electrophysiological study 91 workers of a big car factory performed a series of switch tasks to assess their cognitive control functions. Four groups of workers participated in the study: 23 young and 23 middle aged assembly line employees and 22 young and 23 middle aged employees with flexible job demands like service and maintenance. Participants performed three digit categorisation tasks. In addition to single task blocks, a cue-based (externally guided) and a memory-based (internally guided) task switch block was administered. Compared to young participants, older ones showed the typical RT-decline. No differences between younger and older participants regarding the local switch costs could be detected despite the source of the current task information. In contrast, whereas the groups did not differ in mixing costs in the cued condition, clear performance decrements in the memory-based mixing block were observed in the group of older employees with repetitive work demands. These findings were corroborated by a number of electrophysiological results showing a reduced CNV suggesting an impairment of task specific preparation, an attenuated P3b suggesting reduced working memory capacity and a decreased Ne suggesting deficits in error monitoring in older participants with repetitive job demands. The results are compatible with the assumption that long lasting, unchallenging job demands may induce several neurocognitive impairments which are already evident in the early fifties. Longitudinal studies are needed to confirm this assumption.     

Signaling a switch: Neural correlates of task switching guided by task cues and transition cues

Event‐related brain potentials were used to examine the neural correlates of task switching directed by task cues and transition cues. Task cues signal both a change of task set and the task to implement; in contrast, transition cues signal a change of task set but do not indicate the required task. The data from two experiments revealed that the frontal P2 and reconfiguration slow wave were elicited by task and transition cues and may reflect processes associated with the change detector and task set configuration. Experiment 2 revealed that the frontal positivity and transition parietal slow wave are associated with the retrieval of the prior task set from memory. These data indicate that distinct neural processes that are related to the change detector, task set configuration, and the retrieval of a recently utilized task set from memory support task switching that is guided by task and transition cues.     

Evaluation of mental task strain based on occipital beta activity and subjective rating of task difficulty

Summary Occipital midline beta-2 (Oz₂) amplitudes and subjective ratings of task difficulty were measured in 24 healthy male students, aged 19–23 years, performing four kinds of mental task (transcribing, cancelling, adding, and calculating) at two grades of self-pace (maximum workload and moderate workload) for 5 min each.Significant differences in Oz₂ amplitudes were observed between the tasks at either workload, except between the adding task and the calculating task. However no significant difference in the subjective ratings was observed between the tasks at either workload, except between the adding task and the calculating task or the cancelling task at maximum workload. Thus the Oz₂ amplitude was more sensitive to differentiation of task strain between the mental tasks, than the subjective rating. In comparison with the critical levels deduced previously, it was estimated from the Oz₂ amplitudes that all the tasks at either workload could induce heavy task strain in the subject, except for the cancelling task at moderate workload. From the subjective ratings, however, it was estimated that no task could induce heavy task strain in the subject.It was, moreover, suggested that the Oz₂ amplitudes reflected the difference in the quality of cortical functions and that the subjective ratings of task difficulty were associated with time pressure rather than the quality of cortical functions.     

Effect of mental fatigue caused by mobile 3D viewing on selective attention: An ERP study

This study investigated behavioral responses to and auditory event-related potential (ERP) correlates of mental fatigue caused by mobile three-dimensional (3D) viewing. Twenty-six participants (14 women) performed a selective attention task in which they were asked to respond to the sounds presented at the attended side while ignoring sounds at the ignored side before and after mobile 3D viewing. Considering different individual susceptibilities to 3D, participants' subjective fatigue data were used to categorize them into two groups: fatigued and unfatigued. The amplitudes of d-ERP components were defined as differences in amplitudes between time-locked brain oscillations of the attended and ignored sounds, and these values were used to calculate the degree to which spatial selective attention was impaired by 3D mental fatigue. The fatigued group showed significantly longer response times after mobile 3D viewing compared to before the viewing. However, response accuracy did not significantly change between the two conditions, implying that the participants used a behavioral strategy to cope with their performance accuracy decrement by increasing their response times. No significant differences were observed for the unfatigued group. Analysis of covariance revealed group differences with significant and trends toward significant decreases in the d-P200 and d-late positive potential (LPP) amplitudes at the occipital electrodes of the fatigued and unfatigued groups. Our findings indicate that mentally fatigued participants did not effectively block out distractors in their information processing mechanism, providing support for the hypothesis that 3D mental fatigue impairs spatial selective attention and is characterized by changes in d-P200 and d-LPP amplitudes.     

Mental fatigue, motivation and action monitoring

In this study we examined whether the effects of mental fatigue on behaviour are due to reduced action monitoring as indexed by the error related negativity (Ne/ERN), N2 and contingent negative variation (CNV) event-related potential (ERP) components. Therefore, we had subjects perform a task, which required a high degree of action monitoring, continuously for 2h. In addition we tried to relate the observed behavioural and electrophysiological changes to motivational processes and individual differences. Changes in task performance due to fatigue were accompanied by a decrease in Ne/ERN and N2 amplitude, reflecting impaired action monitoring, as well as a decrease in CNV amplitude which reflects reduced response preparation with increasing fatigue. Increasing the motivational level of our subjects resulted in changes in behaviour and brain activity that were different for individual subjects. Subjects that increased their performance accuracy displayed an increase in Ne/ERN amplitude, while subjects that increased their response speed displayed an increase in CNV amplitude. We will discuss the effects prolonged task performance on the behavioural and physiological indices of action monitoring, as well as the relationship between fatigue, motivation and individual differences.     

Neural correlates of cue retrieval, task set reconfiguration, and rule mapping in the explicit cue task switching paradigm

Event-related brain potentials (ERPs) were used in two experiments to examine the neural correlates of processes underlying task switching in the information-reduction task switching paradigm. Each experiment included 22 participants. The paradigm included two cues for each task. This element of the design allowed us to differentiate the ERP correlates of cue retrieval, task set reconfiguration, and rule mapping. The ERP data revealed a parietal slow wave that was sensitive to processes associated with cue retrieval and task set reconfiguration and a frontal-polar slow wave that was sensitive to processes associated with rule mapping. These findings further the proposal that an endogenous act of control supporting processes related to task set reconfiguration and rule mapping may facilitate performance of the explicit cue task switching paradigm.     

Mental task demands and cardiovascular response patterns

Though it is well known that solving mental tasks elicits tonic increases in cardiovascular activity, a good theory explaining the specificity of this effect is lacking. It is also unclear why different kinds of mental tasks elicit different response patterns. The aim of the experiment was to compare cardiovascular response patterns during three tasks matched for their duration (8 min) and probability of success (.5): a simple RT task and two numeral tasks. One of them (a RUN task) involved program running (performing basic arithmetical operations), the other (an EDIT task) required searching for a problem solution. Seven cardiovascular variables, measured by a Portapres monitor, were analyzed. The analysis showed, among other findings, that the tonic increase in blood pressure and heart rate was greater during the RUN task than during the RT task. On the other hand, the EDIT task and the RT task produced almost identical response patterns.     

Occipital midline EEG and subjective rating of task difficulty as indices of mental task strain

Summary Three measures of mental task strain, namely performance level, occipital midline beta-2 (Oz₂) amplitude and subjective rating of task difficulty, were taken in 34 healthy male students aged 19–24 years as they performed either a paced or a self-paced calculating task for 4 h.The performance levels were so constant throughout the work periods that they were of no use in evaluating mental task strain. The Oz₂ amplitudes increased significantly with the execution of both tasks, and a significant increase took place during the self-paced task work periods. From this, a critical value of Oz₂ amplitude for a heavy task strain was estimated to be about 3.5 V (the difference between the values at work and at rest). The subjective ratings of task difficulty rose linearly with work time in both tasks. The subjective task strain attributable to work time was found to exceed the critical level long before the objective measure. In addition, other results suggest that the Oz₂ activity attributable to task execution is related to the capacity for achieving the task.     

Effect of dried-bonito broth on mental fatigue and mental task performance in subjects with a high fatigue score

Dried-bonito broth is commonly employed as a soup and sauce base in Japanese cuisine and is considered to be a nutritional supplement that promotes recovery from fatigue. Previous human trials suggest that the ingestion of dried-bonito broth improves several mood states; however, its effect on fatigue has not yet been clarified. The aim of this study was to clarify the effects of daily ingestion of dried-bonito broth on fatigue and cognitive parameters by a placebo-controlled double blind crossover trial. Forty-eight subjects with fatigue symptoms ingested the dried-bonito broth or a placebo solution every day for 4 weeks. Mood states were evaluated by the Profile of Mood States (POMS), and mental task performance was evaluated by the Uchida-Kraepelin psychodiagnostic (UKP) test. Fatigue and total mood disturbance (TMD) scores on the POMS test decreased significantly during the dried-bonito broth ingestion (p<0.05), but did not change significantly during placebo ingestion. The change in vigor score during dried-bonito broth ingestion was significantly higher than that during placebo ingestion at 2 weeks (p<0.05). The results of the UKP test indicate that the numbers of both total answers and correct answers significantly increased during dried-bonito broth ingestion (p<0.05), while no significant changes were observed in the placebo ingestion. These results suggest that the daily ingestion of dried-bonito broth may improve the mood states, may reduce mental fatigue and may increase performance on a simple calculation task.     

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.     

A multifaceted investigation of the link between mental fatigue and task disengagement

Mental fatigue is often characterized by reduced motivation for effortful activity and impaired task performance. We used subjective, behavioral (performance), and psychophysiological (P3, pupil diameter) measures during an n‐back task to investigate the link between mental fatigue and task disengagement. After 2 h, we manipulated the rewards to examine a possible reengagement effect. Analyses showed that, with increasing fatigue and time‐on‐task, performance, P3 amplitude, and pupil diameter decreased. After increasing the rewards, all measures reverted to higher levels. Multilevel analysis revealed positive correlations between the used measures with time‐on‐task. We interpret these results as support for a strong link between task disengagement and mental fatigue.