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1.  Effects of Secondary Task on Obstacle Avoidance in Healthy Young Adults 
Research studying attention and gait stability has suggested the process of recovering gait stability requires attentional resources, but the effect of performing a secondary task on stability during obstacle avoidance is poorly understood. Using a dual-task paradigm, the present experiment investigated the extent to which young adults are able to respond to a secondary auditory Stroop task (requiring executive attentional network resources) concurrently with obstacle crossing during gait as compared to performing unobstructed walking or sitting (control task). Our results demonstrated that as the level of difficulty in the postural task increased, there was a significant reduction in verbal response time from congruent to incongruent conditions in the Stroop task, but no differences in gait parameters, indicating that these postural tasks require attention, and that young adults use a strategy of modulating the auditory Stroop task performance while keeping stable gait performance under the dual-task situations. Our findings suggest the existence of a hierarchy of control within both postural task (obstacle avoidance requires the most information processing resources) and dual-task (with gait stability being a priority) conditions.
doi:10.1007/s00221-007-1087-9
PMCID: PMC2556305  PMID: 17717655
2.  Cardiorespiratory Fitness and Attentional Control in the Aging Brain 
A growing body of literature provides evidence for the prophylactic influence of cardiorespiratory fitness on cognitive decline in older adults. This study examined the association between cardiorespiratory fitness and recruitment of the neural circuits involved in an attentional control task in a group of healthy older adults. Employing a version of the Stroop task, we examined whether higher levels of cardiorespiratory fitness were associated with an increase in activation in cortical regions responsible for imposing attentional control along with an up-regulation of activity in sensory brain regions that process task-relevant representations. Higher fitness levels were associated with better behavioral performance and an increase in the recruitment of prefrontal and parietal cortices in the most challenging condition, thus providing evidence that cardiorespiratory fitness is associated with an increase in the recruitment of the anterior processing regions. There was a top-down modulation of extrastriate visual areas that process both task-relevant and task-irrelevant attributes relative to the baseline. However, fitness was not associated with differential activation in the posterior processing regions, suggesting that fitness enhances attentional function by primarily influencing the neural circuitry of anterior cortical regions. This study provides novel evidence of a differential association of fitness with anterior and posterior brain regions, shedding further light onto the neural changes accompanying cardiorespiratory fitness.
doi:10.3389/fnhum.2010.00229
PMCID: PMC3024830  PMID: 21267428
cardiorespiratory fitness; Stroop task; cognitive and attentional control
3.  Neural Congruency Effects in the Multi-Source Interference Task Vanish in Healthy Youth after Controlling for Conditional Differences in Mean RT 
PLoS ONE  2013;8(4):e60710.
According to the conflict monitoring model of cognitive control, reaction time (RT) in distracter interference tasks (e.g., the Stroop task) is a more precise index of response conflict than stimulus congruency (incongruent vs. congruent). The model therefore predicts that RT should be a reliable predictor of activity in regions of the posterior medial frontal cortex (pMFC) that are posited to detect response conflict. In particular, pMFC activity should be (a) greater in slow-RT than in fast-RT trials within a given task condition (e.g., congruent) and (b) equivalent in RT-matched trials from different conditions (i.e., congruent and incongruent trials). Both of these effects have been observed in functional magnetic resonance imaging (MRI) studies of adults. However, neither effect was observed in a recent study of healthy youth, suggesting that (a) the model does not accurately describe the relationship between RT and pMFC activity in this population or (b) the recent study was characterized by high variability due to a relatively small sample size. To distinguish between these possibilities, we asked a relatively large group of healthy youth (n = 28) to perform a distracter interference task - the multi-source interference task (MSIT) - while we recorded their brain activity with functional MRI. In this relatively large sample, both of the model’s predictions were confirmed. We conclude that the model accurately describes the relationship between pMFC activity and RT in healthy youth, but that additional research is needed to determine whether processes unrelated to response conflict contribute to this relationship.
doi:10.1371/journal.pone.0060710
PMCID: PMC3629025  PMID: 23613739
4.  Stroop tasks associated with differential activation of anterior cingulate do not differentiate psychopathic and non-psychopathic offenders 
Attentional models of psychopathy hold that psychopathic individuals fail to process information that conflicts with goal-directed behavior. However, they display normal interference on color-word Stroop tasks. To determine whether psychopathic individuals’ attention deficits are specific to conditions associated with the anterior cingulate (ACC) conflict monitoring system, we administered a Stroop task with a mostly-congruent condition associated with ACC activation, and a mostly-incongruent condition that is not, to 128 criminal offenders assessed for psychopathy using Hare’s (2003) PCL-R. Despite replicating previous condition Effects associated with differential ACC activation (Carter et al., 2000), psychopathic offenders and controls performed very similarly in both conditions. Results do not support an association between ACC-related deficits in conflict monitoring and the attention deficits of psychopathic offenders.
doi:10.1016/j.paid.2006.07.023
PMCID: PMC3137648  PMID: 21765572
Psychopathy; Conflict monitoring; Anterior cingulate cortex
5.  Presbypropria: the effects of physiological ageing on proprioceptive control 
Age  2011;34(5):1179-1194.
Several changes in the human sensory systems, like presbycusis or presbyopia, are well-known to occur with physiological ageing. A similar change is likely to occur in proprioception, too, but there are strong and unexplained discrepancies in the literature. It was proposed that assessment of the attentional cost of proprioceptive control could provide information able to unify these previous studies. To this aim, 15 young adults and 15 older adults performed a position matching task in single and dual-task paradigms with different difficulty levels of the secondary task (congruent and incongruent Stroop-type tasks) to assess presumed age-related deficits in proprioceptive control. Results showed that proprioceptive control was as accurate and as consistent in older as in young adults for a single proprioceptive task. However, performing a secondary cognitive task and increasing the difficulty of this secondary task evidenced both a decreased matching performance and/or an increased attentional cost of proprioceptive control in older adults as compared to young ones. These results advocated for an impaired proprioception in physiological ageing.
doi:10.1007/s11357-011-9300-y
PMCID: PMC3448996  PMID: 21850402
Elderly; Proprioception; Joint position sense; Attention; Sensory integration; Dual task
6.  Adult age differences in the functional neuroanatomy of visual attention: A combined fMRI and DTI study 
Neurobiology of aging  2006;28(3):459-476.
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.
doi:10.1016/j.neurobiolaging.2006.01.005
PMCID: PMC1995072  PMID: 16500004
Aging; Neuroimaging; White matter; Brain activation; Fractional anisotropy; Region of interest; Top-down processing; Visual search; Perception; Cognition; Response time
7.  Prefrontal hypoactivation during cognitive control in early abstinent methamphetamine-dependent subjects 
Psychiatry research  2011;194(3):287-295.
Individuals who abuse methamphetamine (MA) perform at levels below those of healthy controls on tests that require cognitive control. As cognitive control deficits may influence the success of treatment for addiction, we sought to help clarify the neural correlates of this deficit. MA-dependent (n=10, abstinent 4–7 days) and control subjects (n=18) performed a color-word Stroop task, which requires cognitive control, during functional MRI (fMRI). The task included a condition in which participants were required to respond to one stimulus dimension while ignoring another conflicting dimension, and another condition without conflict. We compared the groups on performance and neural activation in the two conditions. MA-dependent subjects made more errors and responded more slowly than controls. Controlling for response times in the incongruent condition, voxel-wise mixed effects analyses (whole-brain corrected) demonstrated that MA-dependent subjects had less activation than control subjects in the right inferior frontal gyrus, supplementary motor cortex/anterior cingulate gyrus and the anterior insular cortex during the incongruent condition only. MA-dependent subjects did not exhibit greater activation in any brain region in either of the Stroop conditions. These preliminary findings suggest that hypofunction in cortical areas that are important for executive function underlies cognitive control deficits associated with MA dependence.
doi:10.1016/j.pscychresns.2011.04.010
PMCID: PMC3225642  PMID: 22047731
Methamphetamine; Stroop; fMRI; cognitive control; prefrontal cortex; insula
8.  Strategic allocation of attention reduces temporally predictable stimulus conflict 
Journal of cognitive neuroscience  2012;24(9):1834-1848.
Humans are able to continuously monitor environmental situations and adjust their behavioral strategies to optimize performance. Here we investigate the behavioral and brain adjustments that occur when conflicting stimulus elements are, or are not, temporally predictable. Event-related potentials (ERPs) were collected while manual-response variants of the Stroop task were performed in which the stimulus onset asynchronies (SOAs) between the relevant-color and irrelevant-word stimulus components were either randomly intermixed, or held constant, within each experimental run. Results indicated that the size of both the neural and behavioral effects of stimulus incongruency varied with the temporal arrangement of the stimulus components, such that the random-SOA arrangements produced the greatest incongruency effects at the earliest irrelevant-first SOA (−200 ms) and the constant-SOA arrangements produced the greatest effects with simultaneous presentation. These differences in conflict processing were accompanied by rapid (~150 ms) modulations of the sensory ERPs to the irrelevant distracter components when they occurred consistently first. These effects suggest that individuals are able to strategically allocate attention in time to mitigate the influence of a temporally predictable distracter. As these adjustments are instantiated by the subjects without instruction, they reveal a form of rapid strategic learning for dealing with temporally predictable stimulus incongruency.
doi:10.1162/jocn_a_00209
PMCID: PMC3632454  PMID: 22360623
Stroop task; conflict processing; event-related potentials (ERPs); incongruency; Stimulus Onset Asynchrony (SOA)
9.  Development of the time course for processing conflict: an event-related potentials study with 4 year olds and adults 
BMC Neuroscience  2004;5:39.
Background
Tasks involving conflict are widely used to study executive attention. In the flanker task, a target stimulus is surrounded by distracting information that can be congruent or incongruent with the correct response. Developmental differences in the time course of brain activations involved in conflict processing were examined for 22 four year old children and 18 adults. Subjects performed a child-friendly flanker task while their brain activity was registered using a high-density electroencephalography system.
Results
General differences were found in the amplitude and time course of event-related potentials (ERPs) between children and adults that are consistent with their differences in reaction time. In addition, the congruency of flankers affected both the amplitude and latency of some of the ERP components. These effects were delayed and sustained for longer periods of time in the children compared to the adults.
Conclusions
These differences constitute neural correlates of children's greater difficulty in monitoring and resolving conflict in this and similar tasks.
doi:10.1186/1471-2202-5-39
PMCID: PMC529252  PMID: 15500693
10.  Impaired Prefrontal Cortical Function and Disrupted Adaptive Cognitive Control in Methamphetamine Abusers: An fMRI Study 
Biological psychiatry  2009;65(8):706-709.
Background
Methamphetamine (MA) abuse is associated with neurotoxicity to frontostriatal brain regions with concomitant deleterious effects on cognitive processes. Deficits in behavioral control are thought to be one contributing factor to the sustainment of addictive behaviors in chronic MA abuse.
Methods
In order to examine patterns of behavioral control relevant to addiction, we employed a fast-event related fMRI design to examine trial to trial reaction time (RT) adjustments in 12 chronic MA abusers who met DSM-IV criteria for MA dependence and 16 non-substance abusing controls. A variant of the Stroop task was employed to contrast the groups on error rates, RT Stroop conflict effect and the level of trial-to-trial adjustments seen after incongruent trials.
Results
The MA abusers exhibited reduced RT adjustments along with reduced activation in the right prefrontal cortex compared to controls on conditions that measured the ability to use exposure to conflict situations (i.e., conflict trials) to regulate behavior. MA abusers did not differ from controls on accuracy rates or within-trial Stroop conflict effects.
Conclusions
The observed deficits in trial to trial RT adjustments suggest that the ability to adapt a behavioral response based on prior experience may be compromised in MA abusers. Such adjustments are critical to everyday functioning and deficits in modifying behavior based on prior events may reflect a key deficit that contributes to maladaptive drug seeking behavior.
doi:10.1016/j.biopsych.2008.11.026
PMCID: PMC2678684  PMID: 19136097
Methamphetamine; prefrontal; attention; fMRI; imaging
11.  Going, Going, Gone: Characterizing the Time-Course of Congruency Sequence Effects 
Performance on traditional selective attention tasks, like the Stroop and flanker protocols, is subject to modulation by trial history, whereby the magnitude of congruency (or conflict) effects is often found to decrease following an incongruent trial compared to a congruent one. These “congruency sequence effects” (CSEs) typically appear to reflect a mesh of memory- and attention-based processes. The current study aimed to shed new light on the nature of the attention-based contribution to CSEs, by characterizing the shape of the CSE time-course while controlling for mnemonic influences. Existing attention-based accounts of CSEs are either ambiguous in their predictions of CSE time-courses, or predict CSEs to persist or grow over the post-stimulus/response interval in anticipation of an upcoming stimulus. We gauged CSE time-courses by systematically varying inter-stimulus (Experiment 1) and response-to-stimulus (Experiment 2) intervals across a wide temporal range, in a face–word Stroop task. In spite of an exponential increase in the likelihood of stimulus appearance with increasing interval duration (i.e., an exponential hazard function), results from both experiments showed CSEs to be most pronounced at the shortest intervals, to quickly decay in magnitude with increasing interval length, and to be absent at longer intervals. These data refute the idea that attentional contributions to CSEs remain static over post-stimulus/response intervals and are incompatible with the notion that CSEs reflect expectation-guided preparatory biasing in anticipation of a forthcoming stimulus. The data are compatible, however, with the notion that attentional contributions to CSEs reflect a short-lived, phasic enhancement of attentional set in reaction to processing conflict.
doi:10.3389/fpsyg.2010.00154
PMCID: PMC3153769  PMID: 21833220
cognitive control; congruency sequence effect; conflict adaptation; attention; expectation
12.  Brain Activation during Interference Resolution in Young and Older Adults: an fMRI Study 
NeuroImage  2010;50(2):810-817.
A rapid event-related fMRI arrow flanker task was used to study aging-associated decline in executive functions related to interference resolution. Older adults had more difficulty responding to Incongruent cues during the flanker task compared to the young adults; the response time difference between the Incongruent and Congruent conditions in the older group was over 50% longer compared to the young adults. In the frontal regions, differential activation (“Incongruent – Congruent” conditions) was observed in the inferior and middle frontal gyri in within-group analyses for both groups. However, the cluster was smaller in the older group and the centroid location was shifted by 19.7 mm. The left superior and medial frontal gyri also appeared to be specifically recruited by older adults during interference resolution, partially driven by errors. The frontal right lateralization found in the young adults was maintained in the older adults during successful trials. Interestingly, bilateral activation was observed when error trials were combined with successful trials highlighting the influence of brain activation associated with errors during cognitive processing. In conclusion, aging appears to result in modified functional regions that may contribute to reduced interference resolution. In addition, error processing should be considered and accounted for when studying age-related cognitive changes as errors may confound the interpretation of task specific age-related activation differences.
doi:10.1016/j.neuroimage.2009.12.087
PMCID: PMC2823923  PMID: 20045067
13.  The Effects of Methylphenidate on Cognitive Control in Active Methamphetamine Dependence Using Functional Magnetic Resonance Imaging 
Methamphetamine (MA) dependence is associated with cognitive deficits. Methylphenidate (MPH) has been shown to improve inhibitory control in healthy and cocaine-dependent subjects. This study aimed to understand the neurophysiological effects before and after acute MPH administration in active MA-dependent and control subjects. Fifteen MA-dependent and 18 control subjects aged 18–46 years were scanned using functional magnetic resonance imaging before and after either a single oral dose of MPH (18 mg) or placebo while performing a color-word Stroop task. Baseline accuracy was lower (p = 0.026) and response time (RT) was longer (p < 0.0001) for the incongruent compared to congruent condition, demonstrating the task probed cognitive control. Increased activation of the dorsolateral prefrontal cortex (DLPFC) and parietal cortex during the incongruent and Stroop effect conditions, respectively was observed in MA-dependent compared to control subjects (p < 0.05), suggesting the need to recruit neural resources within these regions for conflict resolution. Post- compared to pre-MPH treatment, increased RT and DLPFC activation for the Stroop effect were observed in MA-dependent subjects (p < 0.05). In comparison to MPH-treated controls and placebo-treated MA-dependent subjects, MPH-treated MA-dependent subjects showed decreased activation of parietal and occipital regions during the incongruent and Stroop effect conditions (p < 0.05). These findings suggest that in MA-dependent subjects, MPH facilitated increased recruitment of the DLPFC for Stroop conflict resolution, and a decreased need for recruitment of neural resources in parietal and occipital regions compared to the other groups, while maintaining a comparable level of task performance to that achieved pre-drug administration. Due to the small sample size, the results from this study are preliminary; however, they inform us about the effects of MPH on the neural correlates of cognitive control in active MA-dependent subjects.
doi:10.3389/fpsyt.2014.00020
PMCID: PMC3944404  PMID: 24639656
cognitive control; BOLD; drug dependence; fMRI; methamphetamine; methylphenidate; Stroop
14.  Preserved Discrimination Performance and Neural Processing during Crossmodal Attention in Aging 
PLoS ONE  2013;8(11):e81894.
In a recent study in younger adults (19-29 year olds) we showed evidence that distributed audiovisual attention resulted in improved discrimination performance for audiovisual stimuli compared to focused visual attention. Here, we extend our findings to healthy older adults (60-90 year olds), showing that performance benefits of distributed audiovisual attention in this population match those of younger adults. Specifically, improved performance was revealed in faster response times for semantically congruent audiovisual stimuli during distributed relative to focused visual attention, without any differences in accuracy. For semantically incongruent stimuli, discrimination accuracy was significantly improved during distributed relative to focused attention. Furthermore, event-related neural processing showed intact crossmodal integration in higher performing older adults similar to younger adults. Thus, there was insufficient evidence to support an age-related deficit in crossmodal attention.
doi:10.1371/journal.pone.0081894
PMCID: PMC3835740  PMID: 24278464
15.  Congruency sequence effects are driven by previous-trial congruency, not previous-trial response conflict 
Congruency effects in distracter interference tasks are often smaller after incongruent trials than after congruent trials. However, the sources of such congruency sequence effects (CSEs) are controversial. The conflict monitoring model of cognitive control links CSEs to the detection and resolution of response conflict. In contrast, competing theories attribute CSEs to attentional or affective processes that vary with previous-trial congruency (incongruent vs. congruent). The present study sought to distinguish between conflict monitoring and congruency-based accounts of CSEs. To this end, we determined whether CSEs are driven by previous-trial reaction time (RT)—a putative measure of response conflict—or by previous-trial congruency. In two experiments using a face-word Stroop task (n = 49), we found that current-trial congruency effects did not vary with previous-trial RT independent of previous-trial congruency. In contrast, current-trial congruency effects were influenced by previous-trial congruency independent of previous-trial RT. These findings appear more consistent with theories that attribute CSEs to non-conflict processes whose recruitment varies with previous-trial congruency than with theories that link CSEs to previous-trial response conflict.
doi:10.3389/fpsyg.2013.00587
PMCID: PMC3761159  PMID: 24027550
congruency sequence effects; conflict monitoring; reaction time; face-word Stroop; sequential modulations
16.  Effects of motivation on reward and attentional networks: an fMRI study 
Brain and Behavior  2012;2(6):741-753.
Existing evidence suggests that reward and attentional networks function in concert and that activation in one system influences the other in a reciprocal fashion; however, the nature of these influences remains poorly understood. We therefore developed a three-component task to assess the interaction effects of reward anticipation and conflict resolution on the behavioral performance and the activation of brain reward and attentional systems. Sixteen healthy adult volunteers aged 21–45 years were scanned with functional magnetic resonance imaging (fMRI) while performing the task. A two-way repeated measures analysis of variance (ANOVA) with cue (reward vs. non-reward) and target (congruent vs. incongruent) as within-subjects factors was used to test for main and interaction effects. Neural responses to anticipation, conflict, and reward outcomes were tested. Behaviorally there were main effects of both reward cue and target congruency on reaction time. Neuroimaging results showed that reward anticipation and expected reward outcomes activated components of the attentional networks, including the inferior parietal and occipital cortices, whereas surprising non-rewards activated the frontoinsular cortex bilaterally and deactivated the ventral striatum. In turn, conflict activated a broad network associated with cognitive control and motor functions. Interaction effects showed decreased activity in the thalamus, anterior cingulated gyrus, and middle frontal gyrus bilaterally when difficult conflict trials (e.g., incongruent targets) were preceded by reward cues; in contrast, the ventral striatum and orbitofrontal cortex showed greater activation during congruent targets preceded by reward cues. These results suggest that reward anticipation is associated with lower activation in attentional networks, possibly due to increased processing efficiency, whereas more difficult, conflict trials are associated with lower activity in regions of the reward system, possibly because such trials are experienced as less rewarding.
doi:10.1002/brb3.80
PMCID: PMC3500461  PMID: 23170237
Attention; brain reward system; fMRI; motivation; neuroimaging; neuroscience
17.  Rapid modulation of sensory processing induced by stimulus conflict 
Journal of cognitive neuroscience  2010;23(9):2620-2628.
Humans are constantly confronted with environmental stimuli that conflict with task goals and can interfere with successful behavior. Prevailing theories propose the existence of cognitive control mechanisms that can suppress the processing of conflicting input and enhance that of the relevant input. However, the temporal cascade of brain processes invoked in response to conflicting stimuli remains poorly understood. By examining evoked electrical brain responses in a novel, hemifield-specific, visual-flanker task, we demonstrate that task-irrelevant conflicting stimulus input is quickly detected in higher-level executive regions while simultaneously inducing rapid, recurrent modulation of sensory processing in the visual cortex. Importantly, however, both of these effects are larger for individuals with greater incongruency-related reaction time slowing. The combination of neural activation patterns and behavioral interference effects suggest that this initial sensory modulation induced by conflicting stimulus inputs reflects performance-degrading attentional distraction due to their incompatibility, rather than any rapid task-enhancing cognitive control mechanisms. The present findings thus provide neural evidence for a model in which attentional distraction is the key initial trigger for the temporal cascade of processes by which the human brain responds to conflicting stimulus input in the environment.
doi:10.1162/jocn.2010.21575
PMCID: PMC3096678  PMID: 20849233
18.  The controlled imitation task: a new paradigm for studying self-other control 
PeerJ  2013;1:e161.
In the automatic imitation task (AIT) participants make a cued response during simultaneous exposure to a congruent or incongruent action made by another agent. Participants are slower to make the cued response on incongruent trials, which is thought to reflect conflict between the motor representation activated by the cue and the motor representation activated by the observed action. On incongruent trials, good performance requires the capacity to suppress the imitative action, in favor of producing the cued response. Here, we introduce a new experimental paradigm that complements the AIT, and is therefore a useful task for studying the control of self and other activated representations. In what we term the “Controlled Imitation Task (CIT)”, participants are cued to make an action, but on 50% of trials, within 100 ms of this cue, an on-screen hand makes a congruent or incongruent action. If the onscreen hand moves, the participant must suppress the cued response, and instead imitate the observed action as quickly and accurately as possible. In direct contrast to the AIT, the CIT requires suppression of a self-activated motor representation, and prioritization of an imitative response. In experiment 1, we report a robust pattern of interference effects in the CIT, such that participants are slower to make the imitative response on incongruent compared to congruent trials. In experiment 2, we replicate this effect while including a non-imitative spatial-cue control condition to show that the effect is particularly robust for imitative response tendencies per se. Owing to the essentially opposite control requirements of the CIT versus the AIT (i.e., suppression of self-activated motor representations instead of suppression of other-activated motor representations), we propose that this new task is a potentially informative complementary paradigm to the AIT that can be used in studies of self-other control processes.
doi:10.7717/peerj.161
PMCID: PMC3792183  PMID: 24109546
Imitation; Automatic imitation; Controlled imitation; Mirror system; Motor resonance; Automatic imitation Task; Self-related processing; Other-related processing; Self-other control
19.  Attention for speaking: domain-general control from the anterior cingulate cortex in spoken word production 
Accumulating evidence suggests that some degree of attentional control is required to regulate and monitor processes underlying speaking. Although progress has been made in delineating the neural substrates of the core language processes involved in speaking, substrates associated with regulatory and monitoring processes have remained relatively underspecified. We report the results of an fMRI study examining the neural substrates related to performance in three attention-demanding tasks varying in the amount of linguistic processing: vocal picture naming while ignoring distractors (picture-word interference, PWI); vocal color naming while ignoring distractors (Stroop); and manual object discrimination while ignoring spatial position (Simon task). All three tasks had congruent and incongruent stimuli, while PWI and Stroop also had neutral stimuli. Analyses focusing on common activation across tasks identified a portion of the dorsal anterior cingulate cortex (ACC) that was active in incongruent trials for all three tasks, suggesting that this region subserves a domain-general attentional control function. In the language tasks, this area showed increased activity for incongruent relative to congruent stimuli, consistent with the involvement of domain-general mechanisms of attentional control in word production. The two language tasks also showed activity in anterior-superior temporal gyrus (STG). Activity increased for neutral PWI stimuli (picture and word did not share the same semantic category) relative to incongruent (categorically related) and congruent stimuli. This finding is consistent with the involvement of language-specific areas in word production, possibly related to retrieval of lexical-semantic information from memory. The current results thus suggest that in addition to engaging language-specific areas for core linguistic processes, speaking also engages the ACC, a region that is likely implementing domain-general attentional control.
doi:10.3389/fnhum.2013.00832
PMCID: PMC3856851  PMID: 24368899
attentional control; anterior cingulate cortex; superior temporal cortex; picture-word interference; Simon; Stroop; word production
20.  The rapid distraction of attentional resources toward the source of incongruent stimulus input during multisensory conflict 
Journal of cognitive neuroscience  2012;25(4):623-635.
Neuroimaging work on multisensory conflict suggests that the relevant modality receives enhanced processing in the face of incongruency. However, the degree of stimulus processing in the irrelevant modality and the temporal cascade of the attentional modulations in either the relevant or irrelevant modalities are unknown. Here, we employed an audiovisual conflict paradigm with a sensory probe in the task-irrelevant modality (vision) to gauge the attentional allocation to that modality. Event-related potentials (ERPs) were recorded as subjects attended to and discriminated spoken auditory letters while ignoring simultaneous bilateral visual letter stimuli that were either fully congruent, fully incongruent, or partially incongruent (one side incongruent, one congruent) with the auditory stimulation. Half of the audiovisual letter stimuli were followed 500-700 ms later by a bilateral visual probe stimulus. As expected, ERPs to the audiovisual stimuli showed an incongruency ERP effect (fully incongruent versus fully congruent) of an enhanced, centrally distributed, negative-polarity wave starting ~250 ms. More critically here, the sensory ERP components to the visual probes were larger when they followed fully incongruent versus fully congruent multisensory stimuli, with these enhancements greatest on fully incongruent trials with the slowest response times. In addition, on the slowest-response partially incongruent trials, the P2 sensory component to the visual probes was larger contralateral to the preceding incongruent visual stimulus. These data suggest that, in response to conflicting multisensory stimulus input, the initial cognitive effect is a capture of attention by the incongruent irrelevant-modality input, pulling neural processing resources toward that modality, resulting in rapid enhancement, rather than rapid suppression, of that input.
doi:10.1162/jocn_a_00336
PMCID: PMC3662056  PMID: 23249355
21.  The Utility of Stroop Task Switching as a Marker for Early Stage Alzheimer’s Disease 
Psychology and aging  2010;25(3):545-559.
Past studies have suggested attentional control tasks such as the Stroop task and the task switching paradigm may be sensitive to the early detection of Dementia of the Alzheimer type (DAT). The current study combined these tasks to create a Stroop switching task. Performance was compared across young adults, older adults, and individuals diagnosed with “Very Mild” dementia. Results indicated that this task strongly discriminated healthy aging from early stage DAT. In a logistic regression analysis, incongruent error rates from the Stroop Switch discriminated healthy aging from DAT better than any of the other 18 cognitive tasks given in a psychometric battery.
doi:10.1037/a0018498
PMCID: PMC2946107  PMID: 20853964
ALZHEIMER’DISEASE; ATTENTIONAL CONTROL; TASK SWITCHING; DEMENTIA; STROOP
22.  Age-related reorganization of functional networks for successful conflict resolution: A combined functional and structural MRI study 
Neurobiology of aging  2009;32(11):2075-2090.
Aging has readily observable effects on the ability to resolve conflict between competing stimulus attributes that are likely related to selective structural and functional brain changes. To identify age-related differences in neural circuits subserving conflict processing, we combined structural and functional MRI and a Stroop Match-to-Sample task involving perceptual cueing and repetition to modulate resources in healthy young and older adults. In our Stroop Match-to-Sample task, older adults handled conflict by activating a frontoparietal attention system more than young adults and engaged a visuomotor network more than young adults when processing repetitive conflict and when processing conflict following valid perceptual cueing. By contrast, young adults activated frontal regions more than older adults when processing conflict with perceptual cueing. These differential activation patterns were not correlated with regional gray matter volume despite smaller volumes in older than young adults. Given comparable performance in speed and accuracy of responding between both groups, these data suggest that successful aging is associated with functional reorganization of neural systems to accommodate functionally increasing task demands on perceptual and attentional operations.
doi:10.1016/j.neurobiolaging.2009.12.002
PMCID: PMC2888896  PMID: 20022675
Conflict; Stroop; Perceptual Cueing; Functional Reorganization; structural MRI; functional MRI
23.  Corticomotor Responses to Attentionally Demanding Motor Performance: A Mini-Review 
Increased attentional demand has been shown to reduce motor performance, leading to increases in accidents, particularly in elderly populations. While these deficits have been well documented behaviorally, their cortical correlates are less well known. Increased attention has been shown to affect activity in prefrontal regions of the cortex. However there have been varying results within past research investigating corticomotor regions, mediating motor performance. This mini-review initially discusses past behavioral research, before moving to studies investigating corticomotor areas in response to changes in attention. Recent dual task studies have revealed a possible decline in the ability of older, but not younger, adults to activate inhibitory processes within the motor cortex, which may be correlated with poor motor performance, and thus accidents. A reduction in cortical inhibition may be caused by neurodegeneration within prefrontal regions of the cortex with age, rendering older adults less able to allocate attention to corticomotor regions.
doi:10.3389/fpsyg.2013.00165
PMCID: PMC3619619  PMID: 23579267
attention; dual task; inhibition; transcranial magnetic stimulation; motor cortex; mini-review
24.  Proactive and Reactive Control During Emotional Interference and its Relationship to Trait Anxiety 
Brain research  2012;1481:13-36.
In classic Stroop paradigms, increasing the proportion of control-demanding incongruent trials results in strategic adjustments in behavior and implementation of cognitive control processes. We manipulated expectancy for incongruent trials in an emotional facial Stroop task to investigate the behavioral and neural effects of proportion manipulation in a cognitively demanding task with emotional stimuli. Subjects performed a high expectancy (HE) task (65% incongruent trials) and a low expectancy (LE) task (35% incongruent trials) during functional magnetic resonance imaging (fMRI). As in standard Stroop tasks, behavioral interference was reduced in the emotional facial Stroop HE task compared to the LE task. Functional MRI data revealed a switch in cognitive control strategy, from a reactive, event-related activation of a medial and lateral cognitive control network and right amygdala in the LE task to a proactive, sustained activation of right dorsolateral prefrontal cortex (DLPFC) in the HE task. Higher trait anxiety was associated with impairment (slower response time and decreased accuracy) as well as reduced activity in left ventrolateral prefrontal cortex, anterior insula, and orbitofrontal cortex in the HE task on high conflict trials with task-irrelevant emotional information, suggesting that individual differences in anxiety may be associated with expectancy-related strategic control adjustments, particularly when emotional stimuli must be ignored.
doi:10.1016/j.brainres.2012.08.045
PMCID: PMC3541031  PMID: 22960116
amygdala; anterior cingulate cortex; conflict monitoring; fMRI; prefrontal cortex; sustained and transient control
25.  Emotional Body-Word Conflict Evokes Enhanced N450 and Slow Potential 
PLoS ONE  2014;9(5):e95198.
Emotional conflict refers to the influence of task irrelevant affective stimuli on current task set. Previously used emotional face-word tasks have produced certain electrophysiological phenomena, such as an enhanced N450 and slow potential; however, it remains unknown whether these effects emerge in other tasks. The present study used an emotional body-word conflict task to investigate the neural dynamics of emotional conflict as reflected by response time, accuracy, and event-related potentials, which were recorded with the aim of replicating the previously observed N450 and slow potential effect. Results indicated increased response time and decreased accuracy in the incongruent condition relative to the congruent condition, indicating a robust interference effect. Furthermore, the incongruent condition evoked pronounced N450 amplitudes and a more positive slow potential, which might be associated with conflict-monitoring and conflict resolution. The present findings extend our understanding of emotional conflict to the body-word domain.
doi:10.1371/journal.pone.0095198
PMCID: PMC4018289  PMID: 24819150

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