A study on the response selection and inhibition in a cognitive conflict task using event-related potentials

This study examined the hypothesis (Eriksen & Schultz, 1979) that a subject checks whether a prepared response is correct or not in the Eriksen and Eriksen (1974) cognitive conflict task, using event-related potentials (ERPs). Fourteen right-handed subjects were required to respond selectively to a central target letter flanked with compatible (e.g., HHHHHHH) or incompatible (e.g., SSSHSSS) noise letters, or not to respond to asterisks (*******). The results showed that the lateralized readiness potential indicating an incorrect preparation and the NO-GO potential reflecting a response inhibition emerged for incompatible stimuli. These findings indicate that a prepared response was recognized as erroneous, and was inhibited. Therefore, it is suggested that the check operation functioned in the cognitive conflict task. Furthermore, the result that the NO-GO potential latency for incompatible stimuli was longer than that for NO-GO stimuli suggests that the timing of NO-GO decision and response inhibition by the check operation influenced the NO-GO potential latency.     

Perceptual factors affecting age-related differences in focused attention: Performance and psychophysiological analyses

In this study, the impact of two perceptual factors, feature similarity and spacing, on age-related differences in performance and psychophysiological measures were investigated within a focused attention paradigm. Young and old subjects performed an Eriksen letter identification task, in which centrally presented targets were flanked by response-compatible or response-incompatible letters. In feature similarity conditions, targets and flankers had a low or high amount of feature overlap. In spacing conditions, flankers were presented at four different lateral positions from the target. In the condition with high feature overlap and shortest target-flanker distance, old subjects showed greater interference by incompatible flankers than young subjects. Feature similarity was of little influence on age-related differences. However, spacing turned out to be of critical importance. Age-related interference effects disappeared when the target-flanker distance increased. This appears to be due to a decrease in response competition.     

Anticipated action consequences as a nexus between action and perception: evidence from event-related potentials

We used high-density event-related potentials (ERP) in a modified flanker paradigm to study the role of anticipated action consequences in action planning and the role of anticipation in the perception of action consequences. Prior to the experiment, participants were trained to classify target letters in a four-alternative forced-choice task; another letter was presented as an effect following each response. After participants had thus acquired the response-effect contingencies, in the experiment effect letters were presented as flankers to target letters. Effect-compatible flankers were letters that were learned as effects of the correct response to the target; effect-incompatible ones were learned as effects of other responses; neutral flankers were never presented as action effects. To help distinguish early and late effects of flankers on target processing, flankers were presented either simultaneously with the target or after a delay. We found that effect-incompatible flankers resulted in longer, than other flankers, time between the onset of the response-locked lateralized readiness potential and the response, indicating extended motor processing. ERP evoked by the effect-incompatible flankers differed from those evoked by other flankers in early perceptual component P1 and in later frontal component P2 reflecting stimulus evaluation and conflict detection. These results show that anticipating action consequences involves brain systems ranging from perceptual to executive; anticipated action effects constitute a link between perception and action.     

Response activation impairments in schizophrenia: evidence from the lateralized readiness potential

Previous research has demonstrated deficits in preresponse motor activity in schizophrenia, as evidenced by a reduced lateralized readiness potential (LRP). The LRP deficit could be due to increased activation of the incorrect response (e.g., failure to suppress competition) or to reduced activation of the correct response (e.g., a low-level impairment in response preparation). To distinguish these possibilities, we asked whether the LRP impairment is increased under conditions of strong response competition. We manipulated the compatibility of stimulus-response mappings (Experiment 1) and the compatibility of the target with flankers (Experiment 2). In both experiments, the patient LRP was reduced as much under conditions of low response competition as under high competition. These results are incompatible with a failure of patients to suppress competition and are instead consistent with a deficit in activating the correct response.     

Evidence of a divided-attention advantage in autism

People with autism spectrum disorders appear to have some specific advantages in visual processing, including an advantage in visual search tasks. However, executive function theory predicts deficits in tasks that require divided attention, and there is evidence that people with autism have difficulty broadening their attention (Mann & Walker, 2003). We wanted to know how robust the known attentional advantage is. Would people with autism have difficulty dividing attention between central and peripheral tasks, as is required in the Useful Field of View task, or would they show an advantage due to strengths in visual search? Observers identified central letters and localized peripheral targets under both focused- and divided-attention conditions. Participants were 20 adults with high-functioning autism and Asperger's syndrome and 20 adults matched to the experimental group on education, age, and IQ. Contrary to some predictions, individuals with autism tended to show relatively smaller divided-attention costs than did matched adults. These results stand in stark contrast to the predictions of some prevalent theories of visual and cognitive processing in autism.     

The lateralized readiness potential: relationship between human data and response activation in a connectionist model.

Psychophysiological measures such as the lateralized readiness potential (LRP) have been used to study information processing in the Eriksen flankers task. The data provided by these measures are consistent with a continuous flow theory, which proposes that the output of stimulus evaluation is continuously available to the response channels. Cohen et al. (1992) realized this theory in a connectionist model and showed that its behavior corresponded to that of human subjects in the flankers task. We report here a modification of the model and an analysis of the degree to which simulated LRPs (based on the activation functions of the response units of the model) resemble the actual LRPs of human subjects in the same task. Across a variety of different experimental conditions and outcomes, there was a marked correspondence between the simulated and actual LRPs. These observations strengthen the propriety of the connectionist model and of the continuous flow theory on which it is based.     

Proactive and reactive control in S-R compatibility: a brain potential analysis

We investigated how proactive and reactive control facilitates performance in mixed stimulus-response compatibility (SRC) tasks. SRC effects were eliminated in mixed tasks and reversed following incompatible trials. In mixed tasks, early preferential response activation was present in stimulus-locked lateralized readiness potentials (LRPs) but reduced following incompatible trials. In event-related potentials (ERPs), stimulus-locked N2 was enhanced in all mixed trials but was not significantly influenced by the preceding trial. A response-locked fronto-central negative component (N-120), peaking just before the response, was largest for mixed compatible trials preceded by incompatible trials. This N-120 was paired with an enhancement to the peak of the response-locked LRP. Proactive control is involved in selection of an S-R mapping via the indirect route of a dual-route model. Reactive control corrects the S-R mapping, particularly when alternating between S-R mappings.     

Adult age differences in the functional neuroanatomy of visual attention: a combined fMRI and DTI study

We combined measures from event-related functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI), and cognitive performance (visual search response time) to test the hypotheses that differences between younger and older adults in top-down (goal-directed) attention would be related to cortical activation, and that white matter integrity as measured by DTI (fractional anisotropy, FA) would be a mediator of this age-related effect. Activation in frontal and parietal cortical regions was overall greater for older adults than for younger adults. The relation between activation and search performance supported the hypothesis of age differences in top-down attention. When the task involved top-down control (increased target predictability), performance was associated with frontoparietal activation for older adults, but with occipital (fusiform) activation for younger adults. White matter integrity (FA) exhibited an age-related decline that was more pronounced for anterior brain regions than for posterior regions, but white matter integrity did not specifically mediate the age-related increase in activation of the frontoparietal attentional network.     

Strategic control and medial frontal negativity: beyond errors and response conflict

Errors in timed choice tasks typically produce an error-related negativity (ERN) in the event-related potential (ERP). The error specificity of the ERN has been challenged by studies showing a correct response negativity (CRN). Forty-five participants engaged in a flanker task in which both compatibility between flankers and target and the probability of compatible flankers were manipulated. Correct responses elicited a CRN, the amplitude of which increased with the degree of mismatch between the presence of conflict and conflict probability, even on low-conflict (compatible) trials. The fronto-central N2 component was larger on high-conflict (incompatible) correct response trials. However, in contrast to some recent accounts, this N2 was largest for highly probable stimuli. These findings suggest revision to models of the effects of conflict on response-related negativity to account for strategic adjustments made in preparation for the response.     

The joint flanker effect: sharing tasks with real and imagined co-actors

The Eriksen flanker task (Eriksen and Eriksen in Percept Psychophys 16:143-149, 1974) was distributed among pairs of participants to investigate whether individuals take into account a co-actor's S-R mapping even when coordination is not required. Participants responded to target letters (Experiment 1) or colors (Experiment 2) surrounded by distractors. When performing their part of the task next to another person performing the complementary part of the task, participants responded more slowly to stimuli containing flankers that were potential targets for their co-actor (incompatible trials), compared to stimuli containing identical, compatible, or neutral flankers. This joint Flanker effect also occurred when participants merely believed to be performing the task with a co-actor (Experiment 3). Furthermore, Experiment 4 demonstrated that people form shared task representations only when they perceive their co-actor as intentionally controlling her actions. These findings substantiate and generalize earlier results on shared task representations and advance our understanding of the basic mechanisms subserving joint action.     

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.     

Age-related spatiotemporal reorganization during response inhibition

As a key high-level cognitive function in human beings, response inhibition is crucial for adaptive behavior. Previous neuroimaging studies have shown that older individuals exhibit greater neural activation than younger individuals during response inhibition tasks. This finding has been interpreted within a neural compensation framework, in which additional neural resources are recruited in response to age-related cognitive decline. Although this interpretation has received empirical support, the precise event-related temporal course of this age-related compensatory neural response remains unexplored. In the present study, we conducted source analysis on inhibition-related ERP components (i.e., N2 and P3) that were recorded while healthy younger and older adults participated in a visual Go/NoGo task. We found that older adults showed increased source current densities of the N2 and P3 components than younger adults, which support previous hemodynamic findings. Further, such age-related differences in neural activation were successfully separated between the N2 and P3 periods by source localization analysis. Interestingly, the increased activations in older adults were primarily localized to the right precentral and postcentral gyri during the N2 period, which shifted to the right dorsolateral prefrontal cortex and the right inferior frontal gyrus during the P3 period. Taken together, our results clearly illustrate the spatiotemporal dynamics of age-related functional brain reorganization, and further specify the exact temporal course at the millisecond scale by which age-related compensatory neural responses occur during response inhibition.     

Executive functions and neurocognitive aging: dissociable patterns of brain activity

Studies of neurocognitive aging report altered patterns of brain activity in older versus younger adults performing executive function tasks. We review the extant literature, using activation likelihood estimation meta-analytic methods, to compare age-related differences in the pattern of brain activity across studies examining 2 categories of tasks associated with executive control processing: working memory and inhibition. In a direct contrast of young and older adult activations, older adults engaged bilateral regions of dorsolateral prefrontal cortex as well as supplementary motor cortex and left inferior parietal lobule during working memory. In contrast, age-related changes during inhibitory control were observed in right inferior frontal gyrus and presupplementary motor area. Additionally, when we examined task-related differences within each age group we observed the predicted pattern of differentiated neural response in the younger subjects: lateral prefrontal cortex activity associated with working memory versus right anterior insula/frontal opercular activity associated with inhibition. This separation was largely maintained in older subjects. These data provide the first quantitative meta-analytic evidence that age-related patterns of functional brain change during executive functioning depend on the specific control process being challenged.     

Age-related deficits in component processes of working memory

Working memory deficits in normal aging have been well documented, and studies suggest that high memory load plus the presence of distraction negatively impacts successful memory performance to a greater degree in older individuals. However, characterization of the component processes that are impaired by these task manipulations is not clear. In this behavioral study, younger and older subjects were tested with a delayed-recognition and recall task in which the encoding and delay period were both manipulated. During the encoding period, the subjects were presented with either a single letter or multiple letters at their predetermined forward letter span, and the delay period was either uninterrupted or interrupted with a visual distraction. There was an age-related impairment of working memory recognition accuracy only in the combination of high memory load and distraction. These results suggest that when working memory maintenance systems are taxed, faulty recognition processes may underlie cognitive aging deficits in healthy older individuals.     

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.     

Task-dependent exogenous cuing effects depend on cue modality

Task-dependent exogenous cuing effects on reaction time in detection and discrimination tasks have been ascribed to delayed withdrawal of attention in discrimination tasks. Alternatively, these differences may be due to cue-induced response inhibition in detection tasks. Unimodal and crossmodal versions of the Posner paradigm were examined with short cue-target intervals. Targets above or below fixation required either detection or discrimination responses. Cuing effects were determined for the target-elicited P1 component and for the lateralized readiness potential (LRP). Task-dependent cuing effects on reaction time were found in the unimodal but not in the crossmodal version, but not for the P1 component. The LRP data indicated that inhibition of return in the unimodal detection task had a premotoric locus. These findings suggest that inhibition in the unimodal detection task resulted from speeded motor inhibition triggered by the visual cue.     

Effect of aging on priming of pop-out

In visual search tasks using pop-out stimuli, memory of the stimuli in previous 3 to 10 trials affects search performance in the present trial. This is called priming of pop-out. We examined the adult age difference of the effect with Memory Kernel Analysis (Maljkovic & Nakayama, 1994, 1996). It was revealed that with respect to target color and position, facilitation by the stimulus repetition and inhibition by the stimulus change lasted over the succeeding approximately three to eleven trials in both age groups. While eye movements were frequently observed in older subjects and their reaction times were longer than younger subjects', the priming effect was robustly observed. These results suggest that facilitation and inhibition for pop-out features are intact in older adults. The number of trials the effect persisted was discussed in terms of age-related differences of capacities of the memory mediating the effect.     

Delayed flanker effects on lateralized readiness potentials

When participants were required to respond to a relevant central target and ignore irrelevant flanking stimuli, the flankers produced a response compatibility effect. Electrophysiological studies have shown that irrelevant flanker stimuli can affect the motor system. The present experiments further examined the characteristics of flanker effects on the motor system. Sixty participants responded in the flanker task to arrows (experiment 1) or letters (experiment 2). To examine time and extent of flanker effects on the motor system, target onset was delayed with blocked or random stimulus-onset asynchronies (SOA). With SOA of 0 and 100 ms, flanker effects on behavioral measures were reduced in random as compared to blocked conditions, but enhanced with SOA of 400 ms. With SOA of 400 ms, flanker effects on the early lateralized readiness potentials (LRP) were reduced in blocked as compared to random conditions, indicating that the onset of flanker effects on the LRP was delayed. Response-locked LRPs suggest that flanker and target stimuli activate the motor system successively. Findings challenge current theories of the flanker compatibility effect.     

Error-related processing during a period of extended wakefulness

The nature of error detection as manifested by the error-related negativity was examined in both a Sternberg memory search task and a visual search task. Both tasks were performed in conditions with consistent or varied stimulus-response mapping and loads of three or six letters. After subjects were trained extensively in all conditions, they performed the tasks throughout the night without sleeping. The data suggest that the effectiveness of error detection decreases over time because of a decrease in the quality of perceptual processing. Error detection also suffers when performance requires more search-related resources. In both cases, the representation of the correct response is compromised. These results indicate that error detection depends on the same perceptual and cognitive processes that are required for correct performance.     

Similarities and differences between interference from stimulus position and from direction of an arrow: Behavioral and event-related potential measures

Studies with stimulus–response compatibility (SRC) tasks used the stimulus position (SRC-p) and/or the direction indicated by a central arrow (SRC-d) as irrelevant dimensions. Despite behavioral differences revealed by the distributional analysis (DA), both interferences were established at similar loci on the basis of modulations in the lateralized readiness potential (LRP) and P3b components. Consequently, similar underlying mechanisms were proposed for both interferences. However, comparison of motor processes associated with each task is problematical because each involves different components. In addition, previous studies have frequently used different proportions of trials between conditions, which complicate interpretation of the results because the stimulus probability may modulate P3b. Taking these problems into account, the present study investigated the effects of interference in SRC-p and SRC-d tasks, in which the participants responded to the color of a stimulus while ignoring the position and the direction indicated by a central arrow, respectively. The interference was greater in the SRC-p than in the SRC-d task. The DA showed that stimulus position affected the performance more quickly than the direction of the arrow. The P3b latency was longer and the P3b amplitude was smaller when stimulus position was incompatible. However, no differences in P3b were found in the SRC-d task. Moreover, both types of interference affected response-related processes (LRP-r) similarly. Therefore, the stimulus position and the direction indicated by the stimulus may share a common locus of interference (response execution), but only stimulus position affects P3b component, which constitutes a link between stimulus evaluation and the response selection.