Response conflict theory,error rates and hybrid processing: A reply to McLeod

McLeod (1977) has proposed a parallel processing model of the psychological refractory period quite similar to an earlier model most recently adumbrated by Kantowitz (1974a). This article corrects some erroneous statements made by McLeod about the testability of the response conflict model and emphasizes the importance of error data in distinguishing among conceptually similar models of the PRP effect.     

Decision and Response in Dual-Task Interference

Experiments with two stimuli (S₁and S₂) and two responses suggest the existence of a stage of processing that cannot be shared between two concurrent tasks. Widespread support has been found for the hypothesis that response selection for Task₂is postponed when the S₁to S₂stimulus onset asynchrony (SOA) is short (Pashler, 1994a). At short SOAs, manipulations which impact Task₂processing prior to response selection (e.g., degradation of stimulus quality) have little effect on Task₂response times (RTs). On the other hand, manipulations which are thought to impact response selection or execution (e.g., Stroop interference) always impact Task₂RTs. There is, however, one particularly compelling demonstration that appears to be inconsistent with the response selection bottleneck hypothesis: Karlin and Kestenbaum (1968) report that the RT difference between detection (i.e., 1-choice) and 2-choice discrimination dramatically decreases with decreasing SOA. Given that the primary difference between detection and discrimination is believed to be at response selection, their result may indicate a processing bottleneck at response execution (Keele, 1973). We fail to replicate the Karlin and Kestenbaum result in two substantive replications of Karlin and Kestenbaum's tasks and procedures. In the single experiment in which Karlin and Kestenbaum's result is replicated, a simple response execution bottleneck account is ruled out by the stability of the difference between 2-choice and 3-choice discrimination times across SOA. Two additional experiments demonstrate that response preparation and task strategy do not substantially contribute to the attenuation of response selection-level effects with decreasing SOA.     

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 coactivation 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.     

Speed-accuracy tradeoff in double stimulation: II. Effects on the second response

In the double-stimulation paradigm subjects respond to two successive stimuli. Previous research (Knight & Kantowitz, 1974) showed that a subject's speed-accuracy tradeoff (SAT) strategy interacted with the interval between the two stimuli to determine response performance to the first stimulus. The present experiment examined the influence of SAT strategy on response performance to the second stimulus. Interest focused on effects of SAT strategy upon the psychological refractory period (PRP) effect. If a single mechanism underlies beth first-and second-response performance (e.g., the PRP effect) in double stimulation, effects of SAT upon the second response should be similar to effects upon the first response. Results showed that the PRP effect appeared only when second-response accuracy was stressed. Under speed emphasis double-stimulation second-response latency never exceeded a single-stimulation baseline. This was analogous to first-response latency effects found by Knight and Kantowitz (1974). Response grouping was strongly influenced by SAT strategy and two response-grouping mechanisms were distinguished. Implications of these and interresponse time data for models of double-stimulation performance are discussed.     

Stroop interference: An input and an output phenomenon

Three theories of Stroop interference are considered: perceptual conflict theory (Hock and Egeth, 1970), response competition theory (Morton, 1969) and conceptual encoding theory (Seymour, 1977). The first two fail to provide a full explanation of the available data, and Seymour's evidence is incomplete. Two experiments are reported. In the first, typical Stroop interference occurs in naming colour patches. In the second, subjects responded to colour patches with learned letter name responses. Both stimulus-related (incongruent colour names) and response-related (incongruent letters) distractors produced interference. These results indicate that any theory which assumes only a single locus for interference is incomplete. Conceptual encoding conflict and a modified form of response competition are suggested as possible dual mechanisms for Stroop interference effects.     

Multiple cognitive control effects of error likelihood and conflict

Recent work on cognitive control has suggested a variety of performance monitoring functions of the anterior cingulate cortex such as errors, conflict, error likelihood, and others. Given the variety of monitoring effects, a corresponding variety of control effects on behavior might be expected. This paper explores whether conflict and error likelihood produce distinct cognitive control effects on behavior, as measured by response time. A Change signal task (Brown & Braver, Science 307:1118–1121, 2005) was modified to include conditions of likely errors due to tardy as well as premature responses in conditions with and without conflict. The results discriminate between competing hypotheses of independent versus interacting conflict and error likelihood control effects. Specifically, the results suggest that the likelihood of premature versus tardy response errors can lead to multiple distinct control effects, which are independent of cognitive control effects driven by response conflict. As a whole, the results point to the existence of multiple distinct cognitive control mechanisms and challenge existing models of cognitive control that incorporate only a single control signal.     

Comment on McLeod and Hume, overlapping mental operations in serial performance with preview: Typing

This paper deals with the claim made by McLeod and Hume (this issue) that, for a skilled typist, the rate of responding is controlled by a limit on the number of responses that can be executed simultaneously, not by a limit on response selection. I point out that McLeod and Hume's observations are consistent with various interpretations, including one in which response rates are limited by response selection. I also note the importance of trying to distinguish structural and strategic bottlenecks in speeded responding.     

Now you see it, now you don't: controlling for contingencies and stimulus repetitions eliminates the Gratton effect

The Gratton (or sequential congruency) effect is the finding that conflict effects (e.g., Stroop and Eriksen flanker effects) are larger following congruent trials relative to incongruent trials. The standard account given for this is that a cognitive control mechanism detects conflict when it occurs and adapts to this conflict on the following trial. Others, however, have questioned the conflict adaptation account and suggested that sequential biases might account for the Gratton effect. In two experiments, contingency biases were removed from the task and stimulus repetitions were deleted to control for stimulus bindings. This eliminated the Gratton effect in the response times in both experiments, supporting a non-conflict explanation of the Gratton effect. A Gratton effect did persist in the errors of Experiment 1; however, this effect was not produced by the type of errors (word reading errors) that a conflict adaptation account should predict. Instead, tentative support was found for a congruency switch cost hypothesis. In all, the conflict adaptation account failed to account for any of the reported data. Implications for future work on cognitive control are discussed.     

错误加工的神经机制

错误加工在认知控制和行为监控中起着关键的作用。监控自己的认知和行为结果,觉察到应该的反应和实际的反应之间的差别（即错误）,纠正这种错误并防止再犯是错误加工的主要内容。错误反应或由代表反应错误等负性反馈刺激诱发的ERP相对于正确反应或由代表反应正确等正性反馈刺激诱发的ERP,表现出一个相对负走向的波形变化,称为错误相关负波（error-related negativity, ERN）和反馈相关负波（feedback-related negativity, FRN）,两者都定位于前扣回附近。错误加工神经机制的研究主要集中于前扣回与ERN、错误意识与错误加工、ERN与FRN的关系。对于前扣带回和ERN的功能意义的解释主要有错误检测理论、冲突监控理论、强化学习理论和预期违反假说。目前错误加工神经机制的研究在研究内容、研究方法和理论观点等方面还存在些问题,这些可能是未来进一步的研究方向     

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.     

Parallel processing and the psychological refractory period

The serial processor theory proposed by Welford is the traditional explanation of the delay in responding to the second stimulus presented in psychological refractory period paradigm experiments. This paper reviews results which do not accord either with that theory or with later modifications of it by Smith and Tolkmitt. To explain these results a model is proposed which contains three propositions: (a) parallel processing of concurrent stimuli, (b) fixed total processing capacity, (c) capacity allocation either dependent on the relative difficulty of the stimuli or set by the subject according to experimental instructions. The predictions of this model for the effects of stimulus difficulty and interstimulus interval on reaction time and interresponse interval are computed. These predictions are compared with those of other parallel processing models of the psychological refractory period which have been proposed by Herman and Kantowitz, by Kahneman and by Keele.     

Micro- and macro-adjustments of task set: activation and suppression in conflict tasks

Macro- and micro-adjustment of task set was studied using distributional analyses of performance data (reaction time and accuracy) obtained in a new experiment using the Simon task. Macro-adjustments involved the long-term strategic modifications in response to the relative probability of conflict trials, while micro-adjustment involved trial-by-trial modifications invoked by the commission of incidental errors. These adjustments were examined in detail in distributional analyses of RT and accuracy, which have been shown to be particularly useful in studying the role of activation and suppression in conflict tasks. The modification of behavioral strategies incurred by the commission of errors and by the relative probability that the irrelevant location corresponded to the incorrect response was found to involve a reduced location-driven direct response activation (as reflected in the early portions of the delta plots for accuracy) and a stronger selective suppression of that direct activation (as reflected in the delta plot slopes for RT). When the probability of conflict trials was high, the effects of irrelevant location were already precluded by macro-adjustment, so that error commission had no further micro-adjustment effect on subsequent behavior. These patterns were not disclosed by analysis of overall performance.     

Experiment and theory building

I examine the role of inference from experiment in theory building. What are the options open to the scientific community when faced with an experimental result that appears to be in conflict with accepted theory? I distinguish, in Laudan’s (1977), Nickels’s (1981), and Franklin’s (1993) sense, between the context of pursuit and the context of justification of a scientific theory. Making this distinction allows for a productive middle position between epistemic realism and constructivism. The decision to pursue a new or a revised theory in response to the new evidence may not be fully rationally determined. Nonetheless, it is possible to distinguish the question of whether there is reason to pursue a theory from the question of whether that theory, once it has been pursued over time, solves a problem of interest to science. I argue that, in this context, there is a solid way to distinguish between the contexts of pursuit and of justification, on the basis of a theory’s evidential support and problem-solving ability.     

Error adaptation in mental arithmetic

Until now, error and conflict adaptation have been studied extensively using simple laboratory tasks. A common finding is that responses slow down after errors. According to the conflict monitoring theory, performance should also improve after an error. However, this is usually not observed. In this study, we investigated whether the characteristics of the experimental paradigms normally used could explain this absence. More precisely, these paradigms have in common that behavioural adaptation has little room to be expressed. We therefore studied error and conflict adaptation effects in a task that encounters the richness of everyday life's behavioural adaptation—namely, mental arithmetic, where multiple solution strategies are available. In accordance with our hypothesis, we observed that posterror accuracy increases after errors in mental arithmetic. No support for conflict adaptation in mental arithmetic was found. Implications for current theories of conflict and error monitoring are discussed.     

Error adaptation in mental arithmetic

Until now, error and conflict adaptation have been studied extensively using simple laboratory tasks. A common finding is that responses slow down after errors. According to the conflict monitoring theory, performance should also improve after an error. However, this is usually not observed. In this study, we investigated whether the characteristics of the experimental paradigms normally used could explain this absence. More precisely, these paradigms have in common that behavioural adaptation has little room to be expressed. We therefore studied error and conflict adaptation effects in a task that encounters the richness of everyday life's behavioural adaptation--namely, mental arithmetic, where multiple solution strategies are available. In accordance with our hypothesis, we observed that post-error accuracy increases after errors in mental arithmetic. No support for conflict adaptation in mental arithmetic was found. Implications for current theories of conflict and error monitoring are discussed.     

Conflict adaptation depends on task structure

The dependence of the Simon effect on the correspondence of the previous trial can be explained by the conflict-monitoring theory, which holds that a control system adjusts automatic activation from irrelevant stimulus information (conflict adaptation) on the basis of the congruency of the previous trial. The authors report on 4 experiments showing that conflict adaptation is mediated by task structure as well as previous congruency. Experiment 1 showed that for 2 completely segregated sets of stimulus-response pairs there was no conflict adaptation across sets. However, if the stimulus sets overlapped for 2 separate response sets, conflict adaptation could be observed across the response sets. Experiment 2 showed that this effect was not due to the use of stimulus-response sets lateralized to 1 hemisphere each. Experiment 3 showed that if response sets are common for 2 separate stimulus sets, then conflict adaptation can again be observed across sets. Finally, Experiment 4 showed local control effects in the absence of confounding feature-overlap effects. These results indicate that deployment of control as evidenced by conflict adaptation reflects task structure.     

Challenge and error: critical events and attention-related errors

Attention lapses resulting from reactivity to task challenges and their consequences constitute a pervasive factor affecting everyday performance errors and accidents. A bidirectional model of attention lapses (error ↔ attention-lapse: Cheyne, Solman, Carriere, & Smilek, 2009) argues that errors beget errors by generating attention lapses; resource-depleting cognitions interfering with attention to subsequent task challenges. Attention lapses lead to errors, and errors themselves are a potent consequence often leading to further attention lapses potentially initiating a spiral into more serious errors. We investigated this challenge-induced error ↔ attention-lapse model using the Sustained Attention to Response Task (SART), a GO–NOGO task requiring continuous attention and response to a number series and withholding of responses to a rare NOGO digit. We found response speed and increased commission errors following task challenges to be a function of temporal distance from, and prior performance on, previous NOGO trials. We conclude by comparing and contrasting the present theory and findings to those based on choice paradigms and argue that the present findings have implications for the generality of conflict monitoring and control models.     

On the Nature of the Probe Reaction-Time Task to Uncover the Attentional Demands of Movement

McLeod (1980) reported some findings which showed that no phase of a movement was more attention-demanding than the other phases, contrary to all the results previously reported (e.g., Ells, 1973; Glencross, 1980). However, McLeod used a paradigm in which the two tasks were serial. Each task consisted of a series of 50 reaction time (RT) trials and/or 50 aiming movement trials. In addition to this, the interval of time between a response and the following signal within each series was constant. In order to try to replicate McLeod’s findings, two experiments were conducted in which the response-signal interval was manipulated. The hypothesis was that time certainty associated with a constant interval would facilitate the allocation of time and would thus artificially reduce the interference between tasks. In Experiment I, manual responses were used for the RT task; in Experiment II, they were vocal. Manipulation of the response-signal interval does not change one of the conclusions reached by McLeod: when the RT task involves vocal responses and the results on the RT task are analyzed in terms of response rather than stimulus arrival during the movement, then there is no phase of the movement which is more attention-demanding than the other phases. However, the results of Experiment II in which both the vocal RT task and the movement task significantly deteriorated in the dual-task condition were taken as an indication that the movement studied involved central attentional demands.     

Disentangling posterror and postconflict reduction of interference

Conflict monitoring theory (CMT; Botvinick, Braver, Barch, Carter, & Cohen Psychological Review, 108, 624–652, 2001) states that response conflict, the simultaneous activation of two competing responses, increases task focus and reduces interference from irrelevant information. CMT also defines errors as conflict, and reduced interference effects have consistently been reported following errors (Ridderinkhof Psychological Research, 66, 312–323, 2002). However, previous computations of this posterror reduction of interference (PERI) have overlooked the congruency of the previous trial. This is problematic, because most errors are made on incongruent trials, creating a confound between (previous) accuracy and (previous) congruency. Therefore, it is likely that reduced interference following errors is in fact the congruency sequence effect (i.e., reduced interference following incongruent, relative to congruent, trials). Our results corroborate this idea by demonstrating that participants indeed showed significant PERI following a congruent trial, but inverse PERI following an incongruent trial. These findings are discussed in light of the adaptation-by-binding account (Verguts & Notebaert Psychological Review, 115, 518–525, 2008, Trends in Cognitive Sciences, 13, 252–257, 2009).