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.     

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.     

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.     

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.     

Visual search irregularities in schizophrenia depend on display size switching

Introduction. In past research it has been demonstrated that when performing a visual search task with either one or multiple (4, 7 or 10) stimuli displayed, patients with schizophrenia demonstrate slow response times (RTs) in the display size of one, target‐absent (one‐absent) condition. The goals of the present investigation were to replicate this effect, and to gain an understanding of the underlying cognitive operations by comparing display‐size switch to display‐size repeat trials.

Methods. In two experiments, patients and controls performed a visual search task with either one or four stimuli displayed. In Experiment 1 (one block with mixed switch and repeat trials), RT for display‐size switch trials was compared to RT from display‐size repeat trials. In Experiment 2, the display‐size one and display‐size four conditions were run in separate, homogeneous blocks.

Results. The results demonstrate that the one‐absent slowing effect was eliminated on repeat trials, regardless of whether the switch and repeat trials were mixed or presented in separate blocks.

Conclusions. This set of results suggests that a combination of cueing and switching effects may underlie the one‐absent slowing observed in patients, such that switching to the one‐absent condition is difficult due to insufficient cueing of the relevant cognitive operations. This visual search paradigm is an excellent candidate for inclusion in the development of a neurocognitive profile specific to schizophrenia.     

Task-switching costs have distinct phase-locked and nonphase-locked EEG power effects

Event-related potentials (ERPs) and total time–frequency power analyses have shown that performance costs during task switching are related to differential preparation to switch tasks (switch cost) and repeat the same task (mixing cost) during both proactive control (cue-to-target interval; CTI) and reactive control (post-target). The time–frequency EEG signal is comprised of both phase-locked activity (associated with stimulus-specific processes) and nonphase-locked activity (represents processes thought to persist over longer timeframes and do not contribute to the average ERP). In the present study, we used a cued task-switching paradigm to examine whether phase-locked and nonphase-locked power are differentially modulated by switch and mixing effects in intervals associated with the need for proactive control (CTI) and reactive control (post-target interval). Phase-locked activity was observed in the theta and alpha bands, closely resembled that seen for total power, and was consistent with switch and mixing ERP positivities. Nonphase-locked analyses showed theta and alpha power effects for both switch and mixing effects early in the CTI and as well as more sustained alpha and beta activity around cue onset, and extending from mid-CTI into the post-target interval. Nonphase-locked activity in pretarget alpha and posttarget theta power were both correlated with response time mixing cost. These findings provide novel insight into phase-locked and nonphase-locked activity associated with switch and mixing costs that are not evident with ERP or total time–frequency analyses.     

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.     

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.     

Costs of a predictable switch between simple cognitive tasks following severe closed-head injury

The authors used a predictable, externally cued task-switching paradigm to investigate executive control in a severe closed-head injury (CHI) population. Eighteen individuals with severe CHI and 18 controls switched between classifying whether a digit was odd or even and whether a letter was a consonant or vowel on every 4th trial. The target stimuli appeared in a circle divided into 8 equivalent parts. Presentation of the stimuli rotated clockwise. Participants performed the switching task at both a short (200 ms) and a long (1,000 ms) preparatory interval. Although the participants with CHI exhibited slower response times and greater switch costs, similar to controls, additional preparatory time reduced the switch costs, and the switch costs were limited to the 1st trial in the run. These findings indicate that participants with severe CHI were able to take advantage of time to prepare for the task switch, and the executive control processes involved in the switch costs were completed before the 1st trial of the run ended.     

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.     

Facilitatory effects of an auditory warning stimulus in a visual location identification task and a visual shape identification task

The occurrence of a weak auditory warning stimulus increases the speed of the response to a subsequent visual target stimulus that must be identified. This facilitatory effect has been attributed to the temporal expectancy automatically induced by the warning stimulus. It has not been determined whether this results from a modulation of the stimulus identification process, the response selection process or both. The present study examined these possibilities. A group of 12 young adults performed a reaction time location identification task and another group of 12 young adults performed a reaction time shape identification task. A visual target stimulus was presented 1850 to 2350 ms plus a fixed interval (50, 100, 200, 400, 800, or 1600 ms, depending on the block) after the appearance of a fixation point, on its left or right side, above or below a virtual horizontal line passing through it. In half of the trials, a weak auditory warning stimulus (S1) appeared 50, 100, 200, 400, 800, or 1600 ms (according to the block) before the target stimulus (S2). Twelve trials were run for each condition. The S1 produced a facilitatory effect for the 200, 400, 800, and 1600 ms stimulus onset asynchronies (SOA) in the case of the side stimulus-response (S-R) corresponding condition, and for the 100 and 400 ms SOA in the case of the side S-R non-corresponding condition. Since these two conditions differ mainly by their response selection requirements, it is reasonable to conclude that automatic temporal expectancy influences the response selection process.     

Impairment of movement initiation and execution but not preparation in idiopathic dystonia

Imaging studies have reported impaired activation of the striatum and their frontal projection sites in dsytonia, areas which are considered to play a role in motor preparation, movement initiation and execution. The aim of this study was to investigate the processes of motor preparation, response initiation and execution in patients with idiopathic torsion dystonia (ITD). We assessed 12 patients with ITD and 12 age-matched controls on a number of reaction time (RT) tasks that differed in degree of motor preparation possible. Subjects performed a visual simple RT (SRT) task, an uncued four-choice reaction time (CRT) task and a fully precued four-choice RT task. A stimulus 1-stimulus 2 (S1-S2) paradigm was used. The warning signal/precue (S1) preceded the imperative stimulus (S2) by either 0 ms (no warning signal or precue) 200 ms, 800 ms, 1,600 ms or 3,200 ms. The patients with ITD had significantly slower RTs and movement times than normals across all RT tasks. The unwarned SRT trials were significantly faster than the uncued CRT trials for both groups. For both groups, precued CRTs were significantly faster than the uncued CRTs. The results show that while response initiation and execution are significantly slower in patients with ITD than normals, movement preparation is not quantitatively or qualitatively different. The results are discussed in relation to previous imaging, behavioural and electrophysiological studies and models of fronto-striatal dysfunction in ITD.     

Stimulus and response ERP analyses of a two-level reaction time task

Higher cognitive processes include the ability to reliably transform sensory or mnemonic information. These processes either occur automatically or they are consciously controlled. To compare these two types of information processing, we developed a reaction time task that requires either a rule operation or else a direct sensory association. We were interested in evaluating the brain's electrical activity corresponding to both tasks, using event-related potentials (ERPs). In order to gain complete insight into the electrical activity of a stimulus-response segment, we analyzed the ERPs corresponding to the processing of the stimulus and the ERPs corresponding to the preparation of the response. To complete the analysis, we also evaluated the lateralized readiness potential (LRP) matched to the stimulus and to the response onset. Compared with the sensory association task, rule operation generated a higher negative potential field at frontocentral scalp areas in a latency range of 312–512 ms after the stimulus. In contrast, the LRP showed a negative component in the sensory association task which was absent during the rule operation; the latency of the difference was in the range 374–532 ms after the stimulus. The ERP component obtained by the response onset analysis was more negative in the rule condition up to a latency of –214 ms before the generation of the movement; the effect was localized at frontal and central scalp regions. We failed to find any significant difference in the LRP matched to the response onset. These results suggest that the brain computation of the rule operation takes place approximately in the middle of the stimulus-response time interval and that it is an additive process to the sensory association response.     

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.     

Motor preparation in a memorised delay task

The effect on reaction time (RT) and movement time (MT) of remembering which one of several targets to move to was investigated in 18 participants who completed 416 trials in each task. On each trial, participants moved their index finger from a central, illuminated switch (the stimulus) to one of eight targets located on the circumference of a 6 cm radius circle. A visual cue (illumination of the target) informed the participant of the appropriate target. In the memorised delay task, the cued target was lit for 300 ms followed by a variable (450–750 ms) foreperiod during which the participant was required to remember the location of the target until the stimulus light was extinguished. In the non-memorised delay task, the target remained lit during the entire foreperiod (750–1050 ms) until the response was completed. At the go signal (stimulus light extinguished) participants moved as quickly and accurately as possible to the cued target. Both RT and MT were significantly (p<0.05) longer in the memorised delay task. The increase in RT shows that remembering which target imposed a greater load on motor preparation even though all the information needed for preparing the response was presented in the cue at the beginning of each trial. The increase in MT raises the possibility that movement execution was also programmed during motor preparation.     

EEG delta oscillations index inhibitory control of contextual novelty to both irrelevant distracters and relevant task‐switch cues

Delta oscillations contribute to the human P300 event‐related potential evoked by oddball targets, although it is unclear whether they index contextual novelty (event oddballness, novelty P3, nP3), or target‐related processes (event targetness, target P3b). To examine this question, the electroencephalogram (EEG) was recorded during a cued task‐switching version of the Wisconsin card‐sorting test. Each target card was announced by a tone cueing either to switch or repeat the task. Novel sound distracters were interspersed among trials. Time‐frequency EEG analyses revealed bursts of delta (2–4 Hz) power associated with enhanced nP3 amplitudes to both task‐switch cues and novel distracters—but no association with target P3b. These findings indicate that the P300‐delta response indexes contextual novelty regardless of whether novelty emanates from endogenous (new task rules) or exogenous (novel distracters) sources of information.     

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.     

On the Shift from Anticipatory Heart Rate Deceleration to Acceleratory Recovery: Revisiting the Role of Response Factors

The influence of inducing motor responses of low and high force at different times in the cardiac cycle was examined. A handgrip response was used which allowed the separation of response initiation from response completion. Based on earlier work, we expected initiation, rather than completion, to initiate poststimulus cardiac acceleration. We also thought that preparation for a high force response might alter preparatory changes of interbeat interval differently from preparation for a low force response. Fifteen college-aged male subjects performed a warned reaction time task in which a visual stimulus signalled a handgrip requiring either a high or a low force to close. NoGo trials in which an inhibit signal was presented occurred on 12% of the trials. Stimuli occurred either on the R-wave of the electrocardiogram or 300 ms later. Reaction speed was varied in different trial blocks by rewarding response times of 200 ms (+/- 50 ms), 300 ms, or 400 ms. Results based on the timing of response initiation were essentially identical to those based on the timing of response completion. High force relative to low force was associated with both earlier response initiation and earlier cardiac acceleration. Force did not alter preparatory cardiac deceleration. Force and response speed did, however, alter the level of heart rate after response occurrence. Thus, response initiation (or an earlier response process) appears to induce a cardiac acceleration whose level is influenced by the speed and force of the motor response.     

Facilitation of heartbeat self-detection in a choice task.

Brener and Kluvitse (Psychophysiology 25 (1988) 554) developed a heartbeat self-detection task in which subjects are required to judge the simultaneity of heartbeat sensations and tones presented at six intervals following the onset of each ventricular contraction (0, 100, 200, 300, 400 or 500 ms). They found that most of their participants considered as simultaneous in the intervals of 100, 200 and 300 ms, in comparison to those of 0, 400 and 500 ms. In the research reported here, an adaptation of this task was administered to 32 subjects (16 men, 16 women) to see whether these interval choices would be replicated using a narrower range of values, and if task performance would be affected by the reduction in number of trials from 30 to 20. The interval values of the external stimuli with reference to the R-wave were 150, 200, 250, 300 and 350 ms. The results indicate that there was a clear choice for the intervals of 150 and 200 ms in comparison to the rest and that the performance of participants decreases after 20 trials.     

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.