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.     

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.     

Electrophysiological correlates of feature analysis during visual search

Event-related brain potentials (ERPs) were recorded from normal young adults during visual search tasks in which the stimulus arrays contained either eight identical items (homogeneous arrays) or seven identical items and one deviant item (pop-out arrays). Four experiments were conducted in which different classes of stimulus arrays were designated targets and the remaining stimulus arrays were designated nontargets. In Experiments 1 and 2, both target and nontarget pop-out stimuli elicited an enhanced anterior N2 wave and a contralaterally larger posterior P1 wave, but Experiments 3 and 4 demonstrated that these components do not reflect fully automatic pop-out detection processes. In all four experiments, target pop-outs elicited enlarged anterior P2, posterior N2, occipital P3, and parietal P3 waves. The target-elicited posterior N2 wave contained a contralateral subcomponent (N2pc) that exhibited a focus over occipital cortex in maps of current source density. The overall pattern of results was consistent with guided search models in which preattentive stimulus information is used to guide attention to task-relevant stimuli.     

Electrophysiological correlates of the effect of set size on object switching in working memory

Previous studies have revealed the effect of set size (the number of activated items) on object switching in working memory, but the underlying neural mechanism remains unclear. In this study, participants were asked to first remember two (small size) or three (large size) two-digit numbers and the corresponding geometrical figures as different references for numerical comparison and then compare a series of numbers (10–99) to the reference numbers cued by different geometrical figures. The cue repeated or switched across trials. Behavioral results revealed that the switch cost was greater in the large-size condition than in the small-size condition. Event-related potential results showed that in the N2 component, an interaction was observed between set size and transition, with a significant transition effect (switch minus repeat) in the large-size condition and a non-significant transition effect in the small-size condition. The same interaction was observed in the P3 component, with a larger amplitude difference (switch minus repeat) in the large-size condition than in the small-size condition. These results suggested that when set size is increased, the effort to inhibit the irrelevant items increases, resulting in large cost of object switching in working memory.     

Electrophysiological correlates of language switching in second language learners

This study analyzed the electrophysiological correlates of language switching in second language learners. Participants were native Spanish speakers classified in two groups according to English proficiency (high and low). Event-related potentials (ERPs) were recorded while they read English sentences, half of which contained an adjective in Spanish in the middle of the sentence. The ERP results show the time-course of language switch processing for both groups: an initial detection of the switch driven by language-specific orthography (left-occipital N250) followed by costs at the level of the lexico-semantic system (N400), and finally a late updating or reanalysis process (LPC). In the high proficiency group, effects in the N400 time window extended to left anterior electrodes and were followed by larger LPC amplitudes at posterior sites. These differences suggest that proficiency modulates the different processes triggered by language switches.     

ERP correlates of anticipatory attention: spatial and non-spatial specificity and relation to subsequent selective attention

Brain-based models of visual attention hypothesize that attention-related benefits afforded to imperative stimuli occur via enhancement of neural activity associated with relevant spatial and non-spatial features. When relevant information is available in advance of a stimulus, anticipatory deployment processes are likely to facilitate allocation of attention to stimulus properties prior to its arrival. The current study recorded EEG from humans during a centrally-cued covert attention task. Cues indicated relevance of left or right visual field locations for an upcoming motion or orientation discrimination. During a 1 s delay between cue and S2, multiple attention-related events occurred at frontal, parietal and occipital electrode sites. Differences in anticipatory activity associated with the non-spatial task properties were found late in the delay, while spatially-specific modulation of activity occurred during both early and late periods and continued during S2 processing. The magnitude of anticipatory activity preceding the S2 at frontal scalp sites (and not occipital) was predictive of the magnitude of subsequent selective attention effects on the S2 event-related potentials observed at occipital electrodes. Results support the existence of multiple anticipatory attention-related processes, some with differing specificity for spatial and non-spatial task properties, and the hypothesis that levels of activity in anterior areas are important for effective control of subsequent S2 selective attention.     

Electrophysiological correlates of looking at paintings and its association with art expertise

This study investigated the electrocortical correlates of art expertise, as defined by a newly developed, content-valid and internally consistent 23-item art expertise questionnaire in N = 27 participants that varied in their degree of art expertise. Participants viewed each 50 paintings, filtering-distorted versions of these paintings and plain colour stimuli under free-viewing conditions whilst the EEG was recorded from 64 channels. Results revealed P3b-/LPC-like bilateral posterior event-related potentials (ERP) that were larger over the right hemisphere than over the left hemisphere. Art expertise correlated negatively with the amplitude of the ERP responses to paintings and control stimuli. We conclude that art expertise is associated with reduced ERP responses to visual stimuli in general that can be considered to reflect increased neural efficiency due to extensive practice in the contemplation of visual art.     

Temporal dynamics of lateralized ERP components elicited during endogenous attentional shifts to relevant tactile events

To investigate the temporal dynamics of lateralized event-related brain potential (ERP) components elicited during covert shifts of spatial attention, ERPs were recorded in a task where central visual symbolic cues instructed participants to direct attention to their left or right hand in order to detect infrequent tactile targets presented to that hand, and to ignore tactile stimuli presented to the other hand, as well as all randomly intermingled peripheral visual stimuli. In different blocks, the stimulus onset asynchrony (SOA) between cue and target was 300 ms, 700 ms, or 1,100 ms. Anterior and posterior ERP modulations sensitive to the direction of an attentional shift were time-locked to the attentional cue, rather than to the anticipated arrival of a task-relevant stimulus. These components thus appear to reflect central attentional control rather than the anticipatory preparation of sensory areas. In addition, attentional modulations of ERPs to task-irrelevant visual stimuli were found, providing further evidence for crossmodal links in spatial attention between touch and vision.     

Toward the influence of temporal attention on the selection of targets in a visual search task: An ERP study

We used ERPs to investigate whether temporal attention interacts with spatial attention and feature‐based attention to enhance visual processing. We presented a visual search display containing one singleton stimulus among a set of homogenous distractors. Participants were asked to respond only to target singletons of a particular color and shape that were presented in an attended spatial position. We manipulated temporal attention by presenting a warning signal before each search display and varying the foreperiod (FP) between the warning signal and the search display in a blocked manner. We observed distinctive ERP effects of both spatial and temporal attention. The amplitudes for the N2pc, SPCN, and P3 were enhanced by spatial attention indicating a processing benefit of relevant stimulus features at the attended side. Temporal attention accelerated stimulus processing; this was indexed by an earlier onset of the N2pc component and a reduction in reaction times to targets. Most importantly, temporal attention did not interact with spatial attention or stimulus features to influence visual processing. Taken together, the results suggest that temporal attention fosters visual perceptual processing in a visual search task independently from spatial attention and feature‐based attention; this provides support for the nonspecific enhancement hypothesis of temporal attention.     

Early posterior ERP components do not reflect the control of attentional shifts toward expected peripheral events

Previous experiments investigating ERP correlates of anticipatory attention shifts triggered by central symbolic cues have identified a contralateral "early directing attention negativity," which was assumed to be generated by processes involved in the control of spatial orienting. Here we demonstrate that this component is not directly linked to the control of attentional shifts, but instead reflects the selection of task-relevant aspects of cue stimuli. In contrast, later ERP components triggered during covert attentional shifts are insensitive to physical cue attributes, and thus appear to be genuine electrophysiological correlates of covert attentional control mechanisms.     

The neural correlates of cognitive effort in anxiety: effects on processing efficiency

We investigated the neural correlates of cognitive effort/pre-target preparation (Contingent Negative Variation activity; CNV) in anxiety using a mixed antisaccade task that manipulated the interval between offset of instructional cue and onset of target (CTI). According to attentional control theory (Eysenck et al., 2007) we predicted that anxiety should result in increased levels of compensatory effort, as indicated by greater frontal CNV, to maintain comparable levels of performance under competing task demands. Our results showed that anxiety resulted in faster antisaccade latencies during medium compared with short and long CTIs. Accordingly, high-anxious individuals compared with low-anxious individuals showed greater levels of CNV activity at frontal sites during medium CTI suggesting that they exerted greater cognitive effort and invested more attentional resources in preparation for the task goal. Our results are the first to demonstrate the neural correlates of processing efficiency and compensatory effort in anxiety and are discussed within the framework of attentional control theory.     

Electrophysiological correlates of direct selection by color

We report an experiment using event-related potentials (ERPs) to study selection by color uncontaminated from selection by location. Participants monitored an RSVP sequence for a given target letter that could appear in upper- or lowercase. Prior to the sequence, a cue indicated the most likely color of the target letter. Replicating E. Vierck and J. Miller (2005), upper-/lowercase discrimination accuracy was higher following valid than invalid color cues. Within the ERPs, the target onset produced a negative component between 150 and 350 ms at occipital sites, with shorter latencies following valid than invalid cues. We also found larger amplitude components for valid than invalid color cues at central and parietal sites between 150 and 325 ms. The results not only demonstrate clear effects of color cuing on both behavior and ERPs but also suggest that the observed ERP differences between valid versus invalid trials mediate the behavioral effects.     

Electrophysiological revelations of trial history effects in a color oddball search task

In visual oddball search tasks, viewing a no‐target scene (i.e., no‐target selection trial) leads to the facilitation or delay of the search time for a target in a subsequent trial. Presumably, this selection failure leads to biasing attentional set and prioritizing stimulus features unseen in the no‐target scene. We observed attention‐related ERP components and tracked the course of attentional biasing as a function of trial history. Participants were instructed to identify color oddballs (i.e., targets) shown in varied trial sequences. The number of no‐target scenes preceding a target scene was increased from zero to two to reinforce attentional biasing, and colors presented in two successive no‐target scenes were repeated or changed to systematically bias attention to specific colors. For the no‐target scenes, the presentation of a second no‐target scene resulted in an early selection of, and sustained attention to, the changed colors (mirrored in the frontal selection positivity, the anterior N2, and the P3b). For the target scenes, the N2pc indicated an earlier allocation of attention to the targets with unseen or remotely seen colors. Inhibitory control of attention, shown in the anterior N2, was greatest when the target scene was followed by repeated no‐target scenes with repeated colors. Finally, search times and the P3b were influenced by both color previewing and its history. The current results demonstrate that attentional biasing can occur on a trial‐by‐trial basis and be influenced by both feature previewing and its history.     

Electrophysiological correlates of change detection

To identify electrophysiological correlates of change detection, event-related brain potentials (ERPs) were recorded while participants monitored displays containing four faces in order to detect a face identity change across successive displays. Successful change detection was mirrored by an N2pc component at posterior electrodes contralateral to the side of a change, suggesting close links between conscious change detection and attention. ERPs on undetected-change trials differed from detected-change and no-change trials. We suggest that short-latency ERP differences between these trial types reflect trial-by-trial fluctuations in advance task preparation, whereas differences in the P3 time range are due to variations in the duration of perceptual and decision-related processing. Overall, these findings demonstrate that ERPs are a useful tool for dissociating processes underlying change blindness and change detection.     

The role of left and right intraparietal sulcus in the attentional blink: a transcranial magnetic stimulation study

Processing of one visual target (T1) makes it difficult to become aware of a second target (T2), when two targets, embedded in a stream of distractor stimuli, occur within about 500 ms. This phenomenon is known as attentional blink (AB) and reflects the temporal limitation in allocating visual attention. Although several studies suggest that parietal regions are concerned with the AB phenomenon, their functional relevance remains unclear. We investigated whether left and/or right intraparietal sulcus (IPS) contributed to the AB bottleneck using transcranial magnetic stimulation (TMS). The course of recovery from the AB deficit was facilitated when single pulse TMS induced a transient interruption of left or right IPS activity at a T1-TMS stimulus onset asynchrony of 350 ms, while there was no effect of TMS or sham stimulation delivered over Cz with the same timing. These results provide direct evidence that activation of left as well as right IPS is involved in the genesis of AB. This finding supports the idea that the IPS plays a critical role in the cortical network controlling the temporal dynamics of visual awareness.     

Cue‐locked lateralized components in a tactile spatial attention task: Evidence for a functional dissociation between ADAN and LSN

ERP studies investigating the control processes responsible for spatial orienting in touch have consistently observed that the anterior directing attention negativity (ADAN) elicited by an attention‐directing cue is followed by a sustained negativity contralateral to the cued hand. Recent evidence suggested that the later negativity, labeled late somatotopic negativity (LSN), might reflect distinct neurocognitive processes from those associated with the ADAN. To investigate the functional meaning of the ADAN and LSN components, we measured ERPs elicited by bilateral tactile cues indicating to covertly shift tactile attention to the left or right hand. Participants performed two spatial attention tasks that differed only for the difficulty of the target/nontarget discrimination at attended locations. The LSN but not the ADAN was sensitive to our experimental manipulation of task difficulty, suggesting that this component might reflect sensory‐specific preparatory processes prior to a forthcoming tactile stimulus.     

Neural correlates of task and source switching: Similar or different?

Controlling everyday behaviour relies on the ability to configure appropriate task sets and guide attention towards information relevant to the current context and goals. Here, we ask whether these two aspects of cognitive control have different neural bases. Electrical brain activity was recorded while sixteen adults performed two discrimination tasks. The tasks were performed on either a visual input (letter on the screen) or self-generated information (letter generated internally by continuing the alphabetical sequence). In different blocks, volunteers either switched between (i) the two tasks, (ii) the two sources of information, or (iii) tasks and source of information. Event-related potentials differed significantly between switch and no-switch trials from an early point in time, encompassing at least three distinct effects. Crucially, although these effects showed quantitative differences across switch types, no qualitative differences were observed. Thus, at least under the current circumstances, switching between different tasks and between perceptually derived or self-generated sources of information rely on similar neural correlates until at least 900 ms after the onset of a switch event.     

ERP correlates of linear hand movements in a motor reproduction task

Blindfolded participants performed one‐dimensional movements towards a mechanical stop and back to the start. After a varying delay, they had to reproduce the encoded target position by a second mechanically unrestricted movement. Average event‐related potentials accompanying the “encoding” and the “reproduction” movements revealed a biphasic waveshape over primary sensorimotor areas. The first negative deflection was the gradually increasing motor potential (MP) that precedes movement onset. This was followed by a second negative component (N4) starting about 100 ms after movement onset. Its amplitude and latency increased with increasing movement distance and reached its maximum in unrestricted movements (i.e., during reproduction) shortly before the deceleration peak. These results show that rapid hand movements are accompanied by non‐continuous and highly distance specific activity changes measured over the sensorimotor cortex.     

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.     

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.