| Jump to a year: | 2007 ~ 2006 ~ 2005 ~ 2004 ~ 2003 ~ 2002 ~ 2000 |
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| 2007 | |
Drink alcohol and dim the lights: The impact of cognitive deficits on medial frontal cortex function
Scalp electroencephalogram (EEG) recordings indicate that regions in medial frontal cortex (MFC) are active following errors. Alcohol consumption reduces this error-related activity, perhaps suggesting that alcohol disrupts the operation of an error monitoring system in MFC. However, it could also be that alcohol consumption affects MFC only indirectly, by impairing stimulus processing and thus making errors harder to detect. This interpretation leads to the prediction that stimulus degradation should likewise reduce error-related activity in MFC. To test this hypothesis, behavioral and EEG data were collected as participants performed a speeded response task with either bright or very dim stimuli. The results using dim stimuli replicated the observed effects of alcohol consumption—with slowed responses accompanied by reduced error-related MFC activity. The sensitivity of MFC to disrupted processing elsewhere in the brain suggests complications in interpreting evidence of disturbed MFC function. Conflict monitoring in cognition-emotion competitions In this chapter we review recent work addressing decisions in which cognitive and emotional demands are simultaneously involved and can at times have opposing effects on behavior. Recent experimental work on three classes of problems—moral decisions, the ultimatum game, and intertemporal choice—has produced a remarkably consistent picture about how decision-making progresses in cases involving competing cognitive and emotional demands. In each of the experimental examples we review, functional MRI (fMRI) data has revealed sets of brain areas that separately correlate with the cognitive and emotional aspects of the task. Further, choices tend to be resolved in favor of which system, cognitive or emotional, has greatest measured activity. When brain activity predominates in the emotion-related brain areas, principally limbic and closely linked cortical areas, choices tend to be resolved in favor of the emotional demand. The opposite choice tends to result when activity predominates in cognition-related areas in dorsolateral prefrontal cortex (DLPFC) and posterior parietal cortex. Theta phase resetting and the error related negativity It has been proposed that the error-related negativity (ERN) is generated by phase resetting of theta-band EEGc oscillations. The present research evaluates a set of analysis methods that have recently been used to provide evidence for this hypothesis. To evaluate these methods, we apply each of them to two simulated data sets: one set that includes theta phase resetting and a second that comprises phasic peaks embedded in EEG noise. The results indicate that the analysis methods do not effectively distinguish between the two simulated data sets. In particular, the simulated data set constructed from phasic peaks, though containing no synchronization of ongoing EEG activity, demonstrates properties previously interpreted as supporting the synchronized oscillation account of the ERN. These findings suggest that the proposed analysismethods cannot provide unambiguous evidence that the ERNis generated by phase resetting of ongoing oscillations. | |
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| 2006 | |
Between-task competition and cognitive control in task switching Cognitive control is required to regulate interactions between brain regions to produce effective, purposeful behavior.Weused functional magnetic resonance imaging to investigate the nature of these interactions and the role of prefrontal cortex (PFC) in cognitive control as subjects switched between simple face and word categorization tasks. Face and word stimuli were used because previous research has shown them to activate distinguishable cortical regions, allowing us to measure levels of activity in task-selective brain regions during task switching. We found that activity in brain regions selective for the currently irrelevant task predicted the behavioral cost associated with switching tasks. This finding supports the theory that between-task competition is a critical determinant of behavior. Task switching was also associated with increased activity in a network of regions implicated in cognitive control, including lateral PFC and parietal cortex. Within this network of regions, we observed dissociations between task-selective and general purpose mechanisms. These findings provide support for theories that propose a control hierarchy comprising regions responsible for maintaining task-specific information about rules or goals, and regions involved in the coordination of these goals. The impact of cognitive deficits on conflict monitoring: Predictable dissociations between the ERN and N2 Monitoring of ongoing processing plays a critical role in regulating cognitive function. Two ERP components, the error-related negativity (ERN) and N2, have been proposed to reflect this monitoring function. Specifically, a recent theory suggests that both components reflect monitoring for response conflict by anterior cingulate cortex (ACC). This view appears to be challenged by findings that alcohol consumption and lesions in ACC have dissociable effects on the ERN and N2. Using a computational model of conflict monitoring, the present research demonstrates that the conflict theory can account for these dissociations in terms of the dissociable effects of alcohol and ACC lesions on processing of relevant stimulus information (that determines ERN amplitude) and processing of irrelevant, distracting information (that determines N2 amplitude). The simulation results suggest new interpretations of the cognitive deficits caused by alcohol consumption (in terms of impaired stimulus processing) and ACC lesions (in terms of impaired attentional control). | |
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| 2005 | |
A mechanism for error detection in speeded response time tasks The concept of error detection plays a central role in theories of executive control. In this article, the authors present a mechanism that can rapidly detect errors in speeded response time tasks. This error monitor assigns values to the output of cognitive processes involved in stimulus categorization and response generation and detects errors by identifying states of the system associated with negative value. The mechanism is formalized in a computational model based on a recent theoretical framework for understanding error processing in humans (C. B. Holroyd & M. G. H. Coles, 2002). The model is used to simulate behavioral and event-related brain potential data in a speeded response time task, and the results of the simulation are compared with empirical data. Neural mechanisms of attention and control: losing our inhibitions? How are we able to focus our attention on the task at hand while ignoring myriad distractions? An elegant neuroimaging study in this issue of Nature Neuroscience finds that, contrary to a widely held view, the prefrontal cortex implements attentional control by amplifying task-relevant information, rather than by inhibiting distracting stimuli. ERP correlates of feedback and reward processing in the presence and absence of response choice The feedback negativity is a component of the event-related brain potential that is elicited by feedback stimuli associated with unfavorable outcomes. The present research investigated whether this component reflects an evaluation of the valence of experienced outcomes or a process of learning about actions that led to those outcomes. The latter hypothesis predicts that a feedback negativity should be observed only when negative outcomes are experienced in relation to executed actions. Contrary to this prediction, feedback negativities were observed in simple monetary gambling tasks in which participants made no active choices (Experiment 1) and no overt actions (Experiment 2). However, the amplitude of the component was reduced in these tasks relative to a gambling task in which the outcomes appeared to be contingent upon participants’ response choices. This reduction was correlated with changes in participants’ subjective ratings of involvement in the tasks, suggesting that the evaluative process indexed by the feedback negativity is sensitive to the motivational significance of ongoing events. Activity in human reward-sensitive brain areas is strongly context dependent Functional neuroimaging research in humans has identified a number of brain areas that are activated by the delivery of primary and secondary reinforcers. The present study investigated how activity in these reward-sensitive regions is modulated by the context in which rewards and punishments are experienced. Fourteen healthy volunteers were scanned during the performance of a simple monetary gambling task that involved a bwinQ condition (in which the possible outcomes were a large monetary gain, a small gain, or no gain of money) and a bloseQ condition (in which the possible outcomes were a large monetary loss, a small loss, or no loss of money). We observed reward-sensitive activity in a number of brain areas previously implicated in reward processing, including the striatum, prefrontal cortex, posterior cingulate, and inferior parietal lobule. Critically, activity in these reward-sensitive areas was highly sensitive to the range of possible outcomes from which an outcome was selected. In particular, these regions were activated to a comparable degree by the best outcomes in each condition–a large gain in the win condition and no loss of money in the lose condition–despite the large difference in the objective value of these outcomes. In addition, some rewardsensitive brain areas showed a binary instead of graded sensitivity to the magnitude of the outcomes from each distribution. These results provide important evidence regarding the way in which the brain scales the motivational value of events by the context in which these events occur. On the ERN and the significance of errors The error-related negativity (ERN) is an event-related brain potential observed when subjects commit errors. To examine whether the ERNis sensitive to the value of errors, themotivational significance of errors was manipulated in two experiments. In Experiment 1, low and high monetary value errors were compared to evaluate the effect of trial value on the ERN. In Experiment 2, subjects performed a flanker task both while their performance was being evaluated and during a control condition. Consistent with the notion that the error-detection system is sensitive to the significance of errors, the ERN was significantly larger on high-value trials in Experiment 1 and during evaluation in Experiment 2. There were no corresponding effects on the correct response negativity, and no behavioral differences between conditions were evident in either experiment. These results are discussed in terms of the functional role of the ERN in response monitoring. | |
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| 2004 | |
The neural basis of error detection: conflict monitoring and the error-related negativity According to a recent theory, anterior cingulate cortex is sensitive to response conflict, the co-activation of mutually incompatible responses. The present research develops this theory to provide a new account of the error-related negativity (ERN), a scalp potential observed following errors. Connectionist simulations of response conflict in an attentional task demonstrated that the ERN—its timing and sensitivity to task parameters—can be explained in terms of the conflict theory. A new experiment confirmed predictions of this theory regarding the ERN and a second scalp potential, the N2, that is proposed to reflect conflict monitoring on correct response trials. Further analysis of the simulation data indicated that errors can be detected reliably on the basis of post-error conflict. It is concluded that the ERN can be explained in terms of response conflict, and that monitoring for conflict may provide a simple mechanism for detecting errors. Detection of synchronized oscillations in the electroencephalogram: an evaluation of methods The signal averaging approach typically used in event-related brain potential (ERP) research assumes that peaks in ERP waveforms reflect neural activity that is uncorrelated with activity in the ongoing EEG. However, this assumption has been challenged by research suggesting that ERP peaks reflect event-related synchronization of ongoing EEG oscillations. Several methods have recently been used to demonstrate that particular ERP peaks result from this kind of event-related synchronization of oscillations. In this study, we investigated the validity of these methods of inference. We simulated epochs of EEG data by superimposing phasic peaks on noise characterized by the power spectrum of the EEG. When applied to the simulated data, the methods in question produced results that have previously been interpreted as evidence of synchronized oscillations, suggesting that the methods can indicate synchronization in conditions where no such synchrony is present. These findings suggest that proposed analysis methods may not effectively disambiguate competing views of the generation of peaks in ERP waveforms. Conflict monitoring: computational and empirical studies In this chapter, we review some of the central results from our work on the conflict monitoring hypothesis, with a focus on the synergistic relationship between computational modeling and empirical work. In addition, we present results from new two studies, which were conducted in response to a recent challenge to the conflict monitoring hypothesis. Relating cognitive and affective theories of the error-related negativity There is currently some debate over whether the error-related negativity reflects the cognitive process of error detection or an appraisal of the affective or motivational significance of detected errors. This article considers the relationship between these cognitive and affective theories of the error-related negativity, with particular focus on how affective theories might be informed by existing cognitive models. It is argued that the approaches should be viewed as complementary rather than opposed, a possibility that is particularly evident when the likely functional role of affective reactions is considered. Sensitivity of electrophysiological activity from medial frontal cortex to utilitarian and performance feedback A recent study (Gehring and Willoughby, 2002a; Science, 295, 2279-2282), has reported the observation in humans of an event-related brain potential component that is sensitive to the value of outcomes in a gambling task. This component, labeled medial frontal negativity (MFN), was most pronounced following monetary losses as opposed to monetary gains. In this study, we investigate the relationship between the MFN and the error-related negativity (ERN), a component elicited by feedback indicating incorrect choice performance. We argue that the two components can be understood in terms of a recently proposed theory that predicts the occurrence of such scalp negativities following each stimulus that indicates that ongoing events are worse than expected. The results from two experiments using a gambling task demonstrate that the sensitivity of the ERN to the utilitarian and performance aspect of the feedback depends on which aspect is most salient. The results are also consistent with a similar scalp topography of the MFN and ERN, providing further support for the view that the two components are manifestations of the same underlying cognitive and neural process. Independent coding of reward magnitude and valence in the human brain Previous research has shown that two components of the event-related brain potential, the P300 and feedback negativity, are sensitive to information about rewards and penalties. The present study investigated the properties of these components in a simple gambling game that required participants to choose between cards that were unpredictably associated with monetary gains and losses of variable magnitude. The aim was to determine the sensitivity of each component to two critical features of reward stimuli: magnitude (small or large) and valence (win or loss). A double dissociation was observed—with the P300 sensitive to reward magnitude but insensitive to reward valence, and the feedback negativity showing the opposite pattern—suggesting that these two fundamental features of rewarding stimuli are evaluated rapidly, and separately, in the human brain. Subsequent analyses provided further evidence of functional dissociations between the feedback negativity and P300. First, the P300, but not the feedback negativity, showed sensitivity to the reward value of alternative, non-selected stimuli. Second, individual differences in the amplitude of the feedback negativity correlated with individual differences in risk-taking behavior observed following monetary losses, whereas individual differences in P300 amplitude were related to behavioral adjustments observed in response to alternative, unchosen outcomes. Dorsal anterior cingulate cortex shows fMRI response to internal and external error signals In our event-related functional magnetic resonance imaging (fMRI) experiment, participants learned to select between two response options by trial-and-error, using feedback stimuli that indicated monetary gains and losses. The results of the experiment indicate that error responses and error feedback activate the same region of dorsal anterior cingulate cortex, suggesting that this region is sensitive to both internal and external sources of error information. Stimulus modality, perceptual overlap, and the Go/NoGo N2 Stimuli that elicit a prepotent but incorrect response are typically associated with an enhanced electrophysiological N2 that is thought to index the operation of a control process such as inhibition or conflict detection. However, recent studies reporting the absence of the N2 modulation in go/no-go tasks involving auditory stimuli challenge this view: It is not clear why inhibition or conflict detection should be sensitive to the modality of the stimulus. Here we present electrophysiological data from a go/no-go task suggesting that the relative size of the N2 modulation in visual and auditory tasks depends on the perceptual overlap between the go and no-go stimuli. Stimuli that looked similar but sounded different were associated with a typical visual N2 modulation and the absence of an auditory N2 modulation, consistent with previous findings. However, when we increased the perceptual overlap between the auditory stimuli, a large no-go N2 was observed. These findings are discussed in terms of existing hypotheses of the N2, and clarify why previous studies have not found an N2 modulation in auditory go/no-go tasks. | |
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| 2003 | |
Errors in reward prediction are reflected in the event-related brain potential The error-related negativity (ERN) is a negative de£ection in the event-related brain potential associated with error processing. A recent theory holds that the ERNis elicited by the impact of a reward prediction error signal carried by the mesencephalic dopamine system on anterior cingulate cortex. The theory predicts that larger ERNs should be elicitedby unexpectedunfavorable outcomes than by expected unfavorable outcomes. We tested the theory in an experiment in which the frequency of occurrence of reward was varied by condition, reasoning that the system that produces the ERN would come to expect non-reward when rewards were infrequent. Consistent with the theory, we found that larger ERNs were elicited by unexpected absences of reward. The effects of recent practice on task switching Four experiments investigated the effect of recent selective practice on the cost of switching between two tasks afforded by letter-digit pairs: alphabet-arithmetic and shape comparison. Experiments 1 and 2 found a greater cost associated with switching to the more recently practiced task: evidence that task-set inertia contributes to switching costs. Experiment 3 found this effect to be limited to trials on which a recently trained stimulus followed another such stimulus: a result problematic for all current theories of task-set priming. Experiment 4 showed that the effect of recent practice was eliminated by active preparation for a task-switch: it appears that endogenous task-set preparation reduces the effects of task-set inertia. Electrophysiological correlates of anterior cingulate function in a Go/NoGo task: effects of response conflict and trial-type frequency Neuroimaging and computational modeling studies have led to the suggestion that response-conflict monitoring by anterior cingulate cortex plays a key role in cognitive control. For example, response conflict is high when a response must be withheld ("NoGo") in contexts in which there is a prepotent tendency to make an overt ("Go") response. An event-related brain potential (ERP) component, the N2, is more pronounced on NoGo as compared to Go trials, and was previously thought to reflect the need to inhibit the Go response. However, the N2 may instead reflect the high degree of response conflict on NoGo trials. If so, an N2 should also be apparent when subjects make a Go response in conditions where NoGo events are more common. To test this hypothesis, we collected high-density ERP data from subjects performing a Go/NoGo task, in which the relative frequency of Go vs. NoGo stimuli was varied. Consistent with our hypothesis, an N2 was apparent on both Go and NoGo trials, and showed the properties expected of an ERP measure of conflict detection on correct trials: (i) it was enhanced for low-frequency stimuli, irrespective of whether these stimuli were associated with generating or suppressing a response; (ii) it was localized to anterior cingulate cortex. This suggests that previous conceptions of the NoGo N2 as indexing response inhibition may be in need of revision. Instead, the results are consistent with the view that the N2 in Go/NoGo tasks reflects conflict arising from competition between the execution and inhibition of a single response. Switching between tasks of unequal familiarity: the role of stimulus-attribute and response-set selection It has been reported that it is harder to switch to a strong, well-practiced task from a weaker, less-practiced task than vice versa. In three experiments we confirmed this surprising asymmetry and investigated how it is affected by a reduction in the degree of interference between tasks. Experiment 1 progressively delayed the onset of the stimulus attribute associated with the stronger task. Experiments 2 and 3 separated the response sets of the tasks. Both manipulations reduced, without eliminating, interference of the stronger with the weaker task, but reversed the asymmetry of switch costs, resulting in a larger cost of switching to the weaker task. The results are interpreted in terms of a model of the interaction between control input, task strength, and task priming. Alcohol and error processing A recent study indicates that alcohol consumption reduces the amplitude of the error-related negativity (ERN), a negative deflection in the electroencephalogram associated with error commission. Here, we explore possible mechanisms underlying this result in the context of two recent theories about the neural system that produces the ERN - one based on principles of reinforcement learning and the other based on response conflict monitoring. | |
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| 2002 | |
Linear spatial integration for single-trial detection in encephalography Conventional analysis of electroencephalography (EEG) and magnetoencephalography (MEG) often relies on averaging over multiple trials to extract statistically relevant differences between two or more experimental conditions. In this article we demonstrate single-trial detection by linearly integrating information over multiple spatially distributed sensors within a predefined time window. We report an average, single-trial discrimination performance of Az ~ 0.80 and fraction correct between 0.70 and 0.80, across three distinct encephalographic data sets. We restrict our approach to linear integration, as it allows the computation of a spatial distribution of the discriminating component activity. In the present set of experiments the resulting component activity distributions are shown to correspond to the functional neuroanatomy consistent with the task (e.g., contralateral sensory–motor cortex and anterior cingulate). Our work demonstrates how a purely data-driven method for learning an optimal spatial weighting of encephalographic activity can be validated against the functional neuroanatomy. Anterior cingulate cortex The anterior cingulate cortex is a region of the brain thought to be involved in actions guided by sensation, cognition, and emotion. This article provides evidence for anterior cingulate cortex function from both human and animal studies using neuroimaging, electrophysiology, lesion, and genetic methodologies. | |
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| 2000 | |
Reconfiguration of task-set: Is it easier to switch to the weaker task? Switching between two tasks afforded by the same stimuli results in slower reactions and more errors on the first stimulus after the task changes. This "switch cost" is reduced, but not usually eliminated, by the opportunity to prepare for a task switch. While there is agreement that this preparation effect indexes a control process performed before the stimulus, the "residual" cost has been attributed to several sources: to a control process essential for task-set reconfiguration that can be carried out only after the stimulus onset, to probabilistic failure to engage in preparation prior to the stimulus, and to two kinds of priming from previous trials: positive priming of the now-irrelevant task and inhibition of the now-relevant task. The main evidence for the carry-over of inhibition is the observation that it is easier to switch from the stronger to the weaker of a pair of tasks afforded by the stimulus than vice versa. We survey available data on interactions between task switching and three manipulations of relative task strength: pre-experimental experience, stimulus-response compatibility, and intra-experimental practice. We conclude that it is far from universally true that it is easier to switch to the weaker task. Either inhibition of the stronger task-set is a strategy used only in the special case of extreme inequality of strength, or its consequences for later performance may be masked by slower post-stimulus control operations for more complex tasks. Inhibitory priming may also be stimulus specific. | |
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