Stimulus and response conflict processing during perceptual decision making

Encoding and dealing with conflicting information is essential for successful decision making in a complex environment. In the present fMRI study, stimulus conflict and response conflict are contrasted in the context of a perceptual decision-making dot-motion discrimination task. Stimulus conflict was manipulated by varying dot-motion coherence along task-relevant and task-irrelevant dimensions. Response conflict was manipulated by varying whether or not competing stimulus dimensions provided evidence for the same or different responses. The right inferior frontal gyrus was involved specifically in the resolution of stimulus conflict, whereas the dorsal anterior cingulate cortex was shown to be sensitive to response conflict. Additionally, two regions that have been linked to perceptual decision making with dot-motion stimuli in monkey physiology studies were differentially engaged by stimulus conflict and response conflict. The middle temporal area, previously linked to processing of motion, was strongly affected by the presence of stimulus conflict. On the other hand, the superior parietal lobe, previously associated with accumulation of evidence for a response, was affected by the presence of response conflict. These results shed light on the neural mechanisms that support decision making in the presence of conflict, a cognitive operation fundamental to both basic survival and high-level cognition.     

Neural correlates of stimulus response and stimulus outcome shifting in healthy participants and MS patients

Introduction

Adaptation to changing situations can be mediated by two strategies: (1) Evaluation of a response and (2) Evaluation of outcome values in relation to objects. Previous studies indicate that response shifting is associated with a network comprising the left frontal cortex and parietal cortex connected by the superior longitudinal fascicle, whereas outcome evaluation is associated with a network consisting of the orbitofrontal cortex, amygdala and uncinate fascicle. However, these studies rarely compared both kinds of adaptation directly and existing fMRI studies with healthy subjects are not informative about the role of the two fiber systems.

Methods

We analyzed stimulus response shifting and stimulus outcome shifting in two studies, one fMRI-study on healthy participants and one study on patients with MS involving structural MRI (Diffusion Tensor Imaging, Voxel Based Morphometry, Ventricular volumetry). Two tasks were used, identical in presentation but different in instruction, controlling for effects of lower level processing. In the SRS task, participants had to perform a “Go” or “NoGo” response depending on a stimulus change: if the stimulus remained the same, they had to continue with the former type of response, if it changed they had to adapt their response pattern. In the SOS task they had to perform a “Go” response only if the presented stimulus corresponded to that of an internal alternating series.

Results

fMRI findings showed that SRS is related to a bilateral parietal-premotor network. In the left hemisphere the prefrontal cortex was also involved. SOS was lateralized to the right hemisphere, particularly to the anterior temporal pole and amygdala, and the inferior parietal cortex. MS patients impaired on this task suffered from lesions in the right uncinate fascicle and showed an enlarged right frontal lateral ventricle.

Conclusion

With physically identical tasks, a functional neuronal segregation can be demonstrated for stimulus response shifting (bilateral activations with a focus in the left prefrontal cortex) and stimulus outcome shifting (right anterior temporal lobe and right supramarginal gyrus).     

Alcohol and cognitive control: implications for regulation of behavior during response conflict

Alcohol intoxication often leads to dysregulated behavior in contexts characterized by conflict between prepotent response tendencies and incompatible alternative responses. Recent research has identified 2 components of an anterior executive attention system that are essential for adaptive behavior when response conflict exists. Event-related potential (ERP) measures of evaluative and regulative cognitive control were collected to determine if impaired executive attention was responsible for observed behavior deficits when intoxicated. Intoxicated participants displayed task performance deficits on incongruent color-naming trials relative to sober controls. Alcohol did not affect P3 magnitude/latency, indicating that timing and integrity of stimulus evaluation remained intact. In contrast, alcohol did reduce frontal components of ERP that index evaluative and regulative cognitive control processes.     

A psychophysiological study on the function of the response‐stop in the Eriksen task1,2

Abstract: In the Eriksen task, we examined the hypothesis ( Iwaki, 1998 ) that a negative event‐related potential, which was enlarged at the frontal site synchronized with the presentation of an erroneous response causing stimulus, is related to the response‐stop function. Fourteen subjects responded selectively with their hands to the stimuli that consisted of a central target letter and surrounding compatible noise letters (e.g., HHHHH) or incompatible noise (e.g., SHHHS for small‐conflict condition or SSHSS for large‐conflict). The results showed that the increased negativity for the incompatible stimuli was synchronized with the stimulus onset but not with the response. Based on the hypothesis above, it is predicted that greater enhancement of an erroneous response by a stimulus causes the response‐stop to work harder in order to avoid an error, and this results in the larger negativity. This was supported by the evidence showing that the negativity was largest for the large‐conflict incompatible stimulus, followed by the small‐conflict, and then the compatible. We also discuss the possibility that the negativity is the NO‐GO potential concerned with the response‐stop function.     

Context-sensitive adjustments of cognitive control: conflict-adaptation effects are modulated by processing demands of the ongoing task

Dynamic adjustments of cognitive control in response to interference from irrelevant stimulus attributes have repeatedly been shown. The purpose of the current research was to investigate how these control adjustments are modulated by the processing demands of a primary task. To this end, the authors combined a primary task (a number comparison task: classifying digits as smaller or larger than 5) with a Simon task. Control adjustments were observed in the form of typical sequential modulations of the Simon effect. In addition, the authors found sequential modulations of the numerical distance effect and an interaction of both effects. Results suggest that not only response conflict due to interference from task-irrelevant features but also processing demands of task-relevant features determine the level of control adjustment in the subsequent trial.     

Approach and avoidance movements are unaffected by cognitive conflict: A comparison of the Simon effect and stimulus–response compatibility

Participants in this study reached from central fixation to a lateral position that either contained or was opposite to the stimulus. Cognitive conflict was induced when the stimulus and response directions did not correspond. In the Simon task, the response direction was cued by the color of the lateral stimulus, and corresponding and noncorresponding trials varied randomly in the same block of trials, resulting in high uncertainty and long reaction times (RTs). In the stimulus-response compatibility (SRC) task, participants reached toward or away from the stimulus in separate blocks of trials, resulting in low uncertainty and short RTs. In the SRC task, cognitive conflict in noncorresponding trials slowed down RTs but hardly affected reach trajectories. In the Simon task, both RTs and reach trajectories were strongly influenced by stimulus-response correspondence. Despite the overall longer RTs in the Simon task, reaches were less direct and deviated toward the stimulus in noncorresponding trials. Thus, cognitive conflict was resolved before movement initiation in the SRC task, whereas it leaked into movement execution in the Simon task. Current theories of the Simon effect, such as the gating of response activation or response code decay, are inconsistent with our results. We propose that the SRC task was decomposed as approaching and avoiding the stimulus, which is sustained by stereotyped visuomotor routines. With complex stimulus-response relationships (Simon task), responses had to be coded as leftward and rightward, with more uncertainty about how to execute the action. This uncertainty permitted cognitive conflict to leak into the movement execution.     

The hierarchy of task decision and response selection: A task-switching event related potentials study

According to “hierarchical” multi-step theories, response selection is preceded by a decision regarding which task rule should be executed. Other theories assume a “flat” single-step architecture in which task information and stimulus information are simultaneously considered. Using task switching, the authors independently manipulated two kinds of conflict: task conflict (with information that potentially triggers the relevant or the competing task rule/identity) and response conflict (with information that potentially triggers the relevant or the competing response code/motor response). Event related potentials indicated that the task conflict effect began before the response conflict effect and carried on in parallel with it. These results are more in line with the hierarchical view.     

The neural basis of cognitive control: Response selection and inhibition

The functional neuroanatomy of tasks that recruit different forms of response selection and inhibition has to our knowledge, never been directly addressed in a single fMRI study using similar stimulus–response paradigms where differences between scanning time and sequence, stimuli, and experimenter instructions were minimized. Twelve right-handed participants were scanned on two standard cognitive control tasks, a stimulus–response incompatibility task, and a response inhibition task. A compound trial design allowed comparison of preparing to inhibit an upcoming automatic response to wholly inhibiting an automatic response. Furthermore, inhibiting an automatic response to perform an alternative task-relevant response was compared to wholly inhibiting an automatic response. No differences were found in prefrontal activity when preparing to inhibit an automatic response was compared to wholly inhibiting an automatic response, suggesting a mostly common network. The left inferior frontal gyrus was found to be commonly recruited during both tasks when controlled responses were required, likely due to its role in response selection. In contrast, the right inferior frontal gyrus was found to be more involved when task demands were stronger for response inhibition. Our results are largely consistent with models of cognitive control that postulate that separate psychological constructs, such as response selection and inhibition, are related processes largely served by a common prefrontal network. This prefrontal network is recruited to a greater or lesser extent depending on specific task demands.     

Modulation of word-reading processes in task switching

The authors examined modulation of the simple act of word naming induced by the conflict arising when that task competes with color naming in a task-switching paradigm. Subjects alternated between naming a word printed in black and naming the color of a stimulus in 2 conditions. In the incongruent condition, the colored stimulus was an irrelevant word generating conflict, and in the neutral condition, color was carried by a row of asterisks. Subjects took substantially longer to name a word printed in black in the incongruent condition, implying a form of suppression. This modulation of the word-naming response was adaptive in that it led to more efficient color naming. The modulation effect was replicated using phoneme detection instead of word naming but not with lexical decision or visual comparison, implicating a phonological encoding process.     

Conflict adaptation is reflected by response interference

The conflict monitoring theory suggests that the occurrence of conflict in previous trials leads to a reduction in interference in current trials through conflict adaption. The present study included two experiments that used a colour-based flanker task and a Stroop task in combination with a 2:1 stimulus-to-response mapping manipulation and a crossing of transition types (Previous trial type×Current trial type) with stimuli to investigate conflict adaption in relation to stimulus and response interference. The results demonstrate that response interference, but not stimulus interference, was reduced following both stimuli and response conflicts in previous trials. In contrast to some recent evidence, we conclude that conflict adaptation is limited to response interference.     

d-Cycloserine: effects on long-term retention of a conditioned response and on memory for contextual attributes.

d-Cycloserine (DCS), a partial agonist of the glycine recognition site of the N-methyl d-aspartate receptor, has beneficial effects on learning and memory. In order to investigate its potential to influence learning and memory of both the response and the stimulus attributes of training, male Sprague-Dawley albino rats were trained in a one-trial inhibitory avoidance task following an acute intraperitoneal injection of DCS (3 mg/kg) or an equal volume of saline. In order to measure memory for stimulus attributes, testing involved a context shift paradigm, in which subjects are tested in either the environment of training or a different one. Good memory for the contextual attributes of training is indicated by poor performance in the alternate context. Retention was assessed either 1, 7, or 14 days after training. At 1 day, Saline subjects were affected by a change in context, while DCS subjects were not. In subjects tested 1 week following training, Saline subjects were no longer affected by a change in context, in that they performed the avoidance response in both contexts. This indicates the forgetting of stimulus attributes in Saline subjects. DCS subjects did show the context shift effect at 1 week, indicating the retention of stimulus attributes. Finally, Saline subjects demonstrated the context shift rebound at 14 days, while DCS subjects performed equivalently in both contexts. Taken together, these data suggest that DCS may enhance retention of fear and slow the forgetting of stimulus attributes.     

Stimulus conflict predicts conflict adaptation in a numerical flanker task

Conflict monitoring theory states that response conflict triggers conflict adaptation, resulting in reduced congruency effects after response-incongruent trials (Botvinick, Braver, Barch, Carter, & Cohen, 2001). Verbruggen, Notebaert, Liefooghe, and Vandierendonck (2006) observed conflict adaptation after stimulus-incongruent trials without any response conflict. In this study, we further explore the hypothesis that stimulus conflict is an important trigger for conflict adaptation. We propose a measure for stimulus conflict that adequately explains the data of Verbruggen et al. and new data from a numerical flanker task. We conclude that stimulus conflict and response conflict have dissociable effects on behavior Whereas response conflict is a good predictor of response times, stimulus conflict is a better predictor of the adaptation effect.     

无意识信息的刺激表征及其时间特性

无意识信息是否存在刺激表征有待解决。实验采用字母Flanker任务, 通过目标和flanker在刺激水平和反应水平上的冲突效应, 重点考察阈下flanker在刺激水平的表征。在相同的实验设计下, flanker可觉察时(实验1A), 观察到经典的刺激冲突效应和反应冲突效应; 而flanker无意识时(实验1B), 重复了反应冲突效应, 却观察到刺激冲突效应发生反转, 提示了无意识信息的反应加工及刺激加工。实验2采用符号材料促使刺激−反应的自动联结, 减少刺激−反应规则的难度, 结果重复了实验1B的发现--无意识信息引起反转的刺激冲突。刺激冲突下反转效应的一致结果表明无意识信息的刺激表征影响了认知加工。实验3考察这种影响在时间进程上的特点。无意识刺激表征的影响随反应时变化：在快速反应中观察到刺激冲突效应, 之后该效应发生反转且反转量随反应时增加而增大。相反, 无意识反应表征的影响在不同反应时下保持稳定。以上结果提供了无意识信息存在刺激表征的行为学证据并揭示了其时间特性, 提供了无意识领域中不一致研究结果的整合思路。     

Base rate effects on the IAT

We investigated the influence of stimulus base rates on the Implicit Association Test (IAT). Using an East/West-German attitude-IAT, we demonstrated that both overall response speed and differential response speed underlying IAT effects depend on the relative frequencies of the stimulus categories. First, when those stimuli that are more common in reality also occurred more frequently in the stimulus list, response speed generally increased. Second, IAT effects increased when congruent blocks profited from the compatibility of frequency-based response biases (i.e., frequent target stimuli and frequent valence stimuli mapped onto the same response key), whereas IAT effects decreased when incongruent trial blocks profited from response compatibility. These findings demonstrate that the stimulus context moderates the magnitude of the IAT effect. Simultaneously, they highlight the need to explore the extent to which implicit measures reflect properties of the task or the environment rather than attributes of test-takers.     

色-词Stroop任务中的冲突类型述评

在认知控制领域中, 色-词Stroop任务常被用于研究冲突加工的内在机制。本文首先简述色-词Stroop任务中的刺激冲突和反应冲突及研究这两类冲突常用的实验范式。然后介绍这两类冲突的神经动力学特征：事件相关电位研究显示, N450的波幅调整反映了大脑对冲突的监测, 持续电位(sustained potential, SP)的波幅调整反映了大脑对反应冲突的解决; 核磁共振成像研究显示, 前扣带回、背外侧前额叶分别在反应冲突的监测、认知控制的执行上扮演着重要的角色。文章最后针对目前研究范式存在的问题提出了改进方法和认知神经研究的新方向。     

Dichotic listening,executive functions and grey matter cortical volume in patients with schizophrenia and healthy controls

Schizophrenia is characterized by cognitive impairment, especially in relation to executive functions. Brain structural abnormalities are also often seen in schizophrenia although little is known of the relationship between cognitive impairment and structural brain changes. Our aim was therefore to investigate this relationship further using MRI and a dichotic listening (DL) task with simple speech sounds and with instructions to focus attention and report only from the left or right ear stimulus. When instructed to focus attention on the left ear syllable a cognitive conflict is induced requiring the allocation of executive resources to be resolved. Grey matter (GM) volume was measured with MRI from four volumes of interests (VOIs), left and right frontal and temporal cortex, respectively, and correlated with DL performance. The results showed significant differences between the groups in their ability to focus attention on and report the left ear stimulus, which was accompanied by reduced GM volume in the left frontal and right temporal lobe VOIs. There was also a significant positive correlation between left frontal GM volume and performance on the DL task, for the groups combined. The results did not support a conclusion that an impairment in cognitive function in schizophrenia was driven by an corresponding impairment in brain structure, since there were no significant correlations when the groups were analyzed separately. It is however concluded that patients with schizophrenia are impaired in executive functions and that they also show reduced GM volumes in left frontal and right temporal lobe areas, compared to healthy controls.     

The effect of positive affect on conflict resolution: Modulated by approach-motivational intensity

The motivational dimensional model of affect proposes that the influence of positive affect on cognitive processing is modulated by approach-motivational intensity. The present research extended this model by examining the influence of positive affect varying in approach-motivational intensity on conflict resolution—the ability to resolve interference from task-irrelevant distractors in order to focus on the target. The global–local task (Experiment 1) and letter-Flanker task (Experiment 2) were used to measure conflict resolution. Additionally, the 4:2 mapping design that assigns two kinds of task-relevant stimuli to one response key and two more to another response key was used in these two tasks to dissociate stimulus and response conflict. Results showed that positive affect varying in approach motivation had opposite influences on conflict resolution. The opposite influences are primarily reflected in low approach-motivated positive affect impairing, while high approach-motivated positive affect facilitating the resolution of response conflict. Conversely, the stimulus conflict was slightly influenced. These findings highlight the utility of distinguishing stimulus and response conflict in future research.     

前额叶神经振荡活动反映了稳固的刺激冲突和反应冲突

为考察典型Flanker任务中练习对刺激冲突和反应冲突的影响,本研究采用练习范式记录被试完成2:1字母Flanker任务时的行为和脑电数据。行为结果发现,练习对这两类冲突无显著影响。神经震荡能量结果发现,前额叶theta能量随练习而显著减弱,这暗示刺激-反应之间的联结因练习而提升;前额叶alpha能量差异不随练习而变化,这可能反映了Flanker任务中稳定的刺激冲突和反应冲突加工机制。因此,本研究揭示了典型Flanker任务中刺激冲突和反应冲突的稳定特征。     

Freeze-Frame: a new infant inhibition task and its relation to frontal cortex tasks during infancy and early childhood

The current study investigated a new, easily administered, visual inhibition task for infants termed the Freeze-Frame task. In the new task, 9-month-olds were encouraged to inhibit looks to peripheral distractors. This was done by briefly freezing a central animated stimulus when infants looked to the distractors. Half of the trials presented an engaging central stimulus, and the other half presented a repetitive central stimulus. Three measures of inhibitory function were derived from the task and compared with performance on a set of frontal cortex tasks administered at 9 and 24 months of age. As expected, infants' ability to learn to selectively inhibit looks to the distractors at 9 months predicted performance at 24 months. However, performance differences in the two Freeze-Frame trial types early in the experiment also turned out to be an important predictor. The results are discussed in terms of the validity of the Freeze-Frame task as an early measure of different components of inhibitory function.     

Dynamics of facilitation and interference in cue-priming and Simon tasks

In examining the selective suppression of responses activated by task-irrelevant stimulus attributes, such as in spatial conflict tasks, two different approaches have pointed to similar conclusions. In one approach (involving cue-priming procedures), variations of the stimulus-onset asynchrony (SOA) between task-irrelevant cues and subsequent target stimuli disclosed that the cues elicit activation of the congruent response, but this activation is subsequently suppressed. In another approach, a series of studies with the Simon task led to the formulation of the activation-suppression hypothesis. Analysis of RT distributions (in particular delta plots) disclosed that the task-irrelevant stimulus location elicits activation of the spatially corresponding response, but this activation is subsequently suppressed. The strength or efficiency of selective response suppression is expressed in the slope of the delta plot. In the present study, we combined these two approaches and found that the effects of SOA manipulation and the results of the distributional analysis converged and were positively correlated, suggesting that they involve a common mechanism of response activation followed by the selective suppression of that activation.