Acta Psychologica. Conflict and error adaptation in the Simon task. Wim Notebaert, Tom Verguts. Contents lists available at ScienceDirect

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1 Acta Psychologica 136 (2011) Contents lists available at ScienceDirect Acta Psychologica journal homepage: www. e lsevier. com/ l ocate/ a ctpsy Conflict and error adaptation in the Simon task Wim Notebaert, Tom Verguts Experimental Psychology, Ghent University, Belgium article info abstract Article history: Received 2 February 2010 Received in revised form 4 May 2010 Accepted 17 May 2010 Available online 17 June 2010 PsycINFO classification: 2340 We present recent empirical and theoretical advances in conflict and error monitoring in the Simon task. On the basis of the adaptation by binding account for conflict adaptation and the orienting account for post-error slowing, we predict a dissociation between conflict and error monitoring. This prediction is tested and confirmed as conflict adaptation is task-specific while post-error slowing is not Elsevier B.V. All rights reserved. Keywords: Simon effect Cognitive control 1. Introduction Cognitive control refers to information processing adjustments in order to optimize task performance, which typically occurs after problems were encountered. One task that has been extremely useful in the study of such control-related adjustments is the Simon task because of its compatibility manipulation (Simon, 1990). The typical problems that call for an adjustment in the Simon task are response conflict and errors. Response conflict occurs on incompatible trials (e.g., stimulus on left location requiring a right response) because on these trials, two opposing responses are activated; one on the basis of the relevant stimulus information, usually color or shape, and one on the basis of the irrelevant stimulus location (e.g., Zorzi & Umiltá, 1995). In most cases response conflict does not result in an error, but sometimes the activation of the incorrect response is so strong that an error is observed. Obviously, errors also occur on compatible trials but less often so and for various reasons (e.g., fluctuations in attention). In the present paper we address the question whether errors and conflict trigger the same behavioral adjustments. The dominant perspective on conflict and error monitoring is that both processes are supported by similar brain areas (Kerns, Cohen, MacDonald, Cho, Stenger, & Carter, 2004) and involve similar computations (Botvinick, Braver, Barch, Carter, & Cohen, 2001; Yeung, Botvinick, & Cohen, 2004). We challenge this mainstream point of view and propose that behavioral adaptation after errors differs from adaptation after conflict. We will review the literature on conflict adaptation specifically focusing on the Simon task and present our computational Corresponding author. Henri Dunantlaan 2, B-9000 Gent, Belgium. address: Wim.notebaert@ugent.be (W. Notebaert). model for conflict adaptation (Verguts & Notebaert, 2008; 2009). We will subsequently present recent work on post-error slowing and describe our orienting account (Notebaert et al., 2009). Interestingly, both accounts predict a dissociation between conflict and error monitoring. This prediction is finally tested in an experiment where Simon and SNARC trials are randomly presented (Notebaert & Verguts, 2008) Conflict adaptation Conflict adaptation was initially demonstrated in the flanker task where the flanker effect was smaller after incongruent trials (N bn) than after congruent trials (N NN; Gratton, Donchin & Coles, 1992). Similarly, conflict adaptation in the Simon task was suggested by the observation that the Simon effect was smaller after incompatible trials than after compatible trials (Notebaert, Soetens, & Melis, 2001; Stürmer, Leuthold, Soetens, Schröter, & Sommer, 2002). One explanation for this Gratton effect is that participants increase control after incompatible trials, for instance, by blocking the processing pathway that processes the irrelevant spatial information (Stürmer et al., 2002). Importantly, in the standard Simon task with two colors, two stimulus locations and two response locations, the data pattern can also be explained in terms of feature repetition and integration effects (Notebaert, Soetens, & Melis, 2001; Hommel, Proctor, & Vu, 2004). Today, there are different versions (e.g., Mayr, Awh, & Laurey, 2003; Nieuwenhuis, Stins, Posthuma, Polderman, Boomsma, & De Geus, 2006) of this alternative account but the main idea is that the data pattern (reduced compatibility effects after incompatible trials) can equally well be described in terms of stimulus and response repetition and alternation effects. More particular, the two trial sequences that /$ see front matter 2010 Elsevier B.V. All rights reserved. doi: /j.actpsy

2 W. Notebaert, T. Verguts / Acta Psychologica 136 (2011) benefit from conflict adaptation are compatible compatible and incompatible incompatible sequences. In a Simon task, and in any other congruency task, these and only these sequences include exact stimulus repetitions (location and color repetition) and complete stimulus alternations (location and color alternation), and it has been demonstrated that complete repetitions and complete alternations are faster than partial repetitions. This effect is typically explained in terms of feature integration effects (Hommel et al., 2004). Very reasonably, researchers raised the question why we should need an extra mechanism (conflict adaptation) for explaining behavioral data that are already explained by a mechanism that also explains different effects? The discussion whether this behavioral pattern reflects conflict adaptation or merely repetition effects continues. In our opinion, however, there are some indications that the effect is not entirely due to repetition effects. A first indication is delivered by electrophysiological studies. Stürmer et al. (2002) showed that the Simon effect disappeared (or even reversed) after incompatible trials. Most interestingly, the data also demonstrated a modulation of the lateralized readiness potential (LRP), which is hard to explain with feature integration and repetition effects. Typically, the LRP shows initial incorrect response activation on incompatible trials, which is then later followed by activation of the correct response. Stürmer et al. showed that this initial incorrect response activation disappeared after incompatible trials. They explained the results in terms of suppression of the irrelevant route after incompatible trials. Additionally, Stürmer, Redlich, Irlbacher, and Brandt (2007) demonstrated that administering transcranial magnetic stimulation (TMS) on left dorsolateral prefrontal cortex (DLPFC) ms preceding the next stimulus abolishes the sequential modulation of the Simon effect. Further support for conflict adaptation was provided by studies demonstrating the behavioral effect in situations where repetitions were excluded. Wühr (2005) investigated this by using four stimulus locations and two response locations. Red and green stimuli were presented on the corners of an imaginary square with a vertical response dimension operated with the left and right hand. Half of the participants responded to the upper key with the left hand and to the lower key with the right hand while this was reversed for the other half of the participants. The reaction times confirmed conflict adaptation in the sense that conflict adaptation was observed for trial types that did not differ in stimulus or response overlap (e.g., when all trials were complete alternations). Akcay and Hazeltine (2007) reached similar conclusions in a Simon task with 4 stimuli, 4 locations and 4 responses. In a further attempt to disrupt all overlap between two consecutive Simon trials, Akcay and Hazeltine (2008; exp. 4) combined two Simon tasks. One was a letter classification task with four letters and the other a color discrimination task with three colors. One task had a vertical stimulus and response arrangement while the other had a horizontal arrangement and both tasks were presented on one side of the fixation cross. The pattern of data showed conflict adaptation on same-side sequences while no conflict adaptation was observed for opposite-side sequences. Because the trials included in this analysis did not contain stimulus or response repetitions, the authors concluded that sequential modulations on the same-side sequences were due to control, which was recruited locally, within one type of Simon task. In sum, conflict adaptation has been observed in a variety of tasks where feature repetitions were excluded. The study by Akcay and Hazeltine (2008) on the other hand suggests that some kind of overlap between trial n-1 and trial n is required, in the sense that conflict in a letter Simon task, does not modulate performance in a subsequent color Simon task. The authors point out that this indicates that cognitive control is a local effect, as opposed to a global (taskaspecific) effect. A similar conclusion was obtained in the study of Notebaert and Verguts (2008). In this study a Simon task was combined with a SNARC task (spatial numerical associations of response codes). The SNARC effect is the observation that small numbers are responded to faster with the left response key and large numbers faster with the right response key (Dehaene, Bossini, & Giraux, 1993). In this particular experiment, participants had to respond to the orientation of the numbers with a left or right response key. The Simon task either used the same relevant information (orientation of a laterally presented X) or different relevant information (color). Both tasks were randomly intermixed and conflict adaptation across the tasks (conflict in Simon trial reduces SNARC effect and conflict in SNARC reduces Simon effect) was only observed in the condition where both tasks used the same relevant information, further supporting the notion of local or task-specific control. In order to explain local or task-specific control effects Verguts and Notebaert (2008; 2009) proposed the adaptation by binding account, which integrates the repetition/integration perspective and the conflict adaptation perspectives. The basic principle is that associations connecting active (stimulus, response, or other) units are strengthened proportional to the amount of conflict on the current trial. For example, when Task 1 is presented, the S R connections of Task 1 are more active than the S R connections of Task 2. Consequently, when conflict occurs, the S R connections of Task 1 will be strengthened to a larger degree than the connections of Task 2. As a result, control is implemented in a task-specific way. A similar associative mechanism was proposed by Blais, Robidoux, Risko, and Besner (2007) and Davelaar and Stevens (2009). Important for the present purposes is that adaptation by binding generates a dissociation between conflict and error monitoring. Before we elaborate on this issue we will first briefly describe recent theoretical advances in the domain of error adaptation Error adaptation Although error adaptation can take on many forms, we will focus here on post-error slowing, the observation that RTs are slower after errors than after correct trials. In the Simon task, this was demonstrated by Ridderinkhof (2002). It is generally thought that post-error slowing reflects a strategic adjustment following an error in order to avoid another error (e.g., Botvinick et al., 2001; Ridderinkhof, 2002). Problematic for explanations in terms of strategic adjustments, however, is that usually accuracy does not improve following errors. In Ridderinkhof (2002) for instance, there was no difference between post-error and post-correct accuracy and others have reported worse performance after errors than after correct trials (e.g., Notebaert et al., 2009). We therefore recently proposed an alternative account for posterror slowing (Notebaert et al., 2009). We postulated that post-error slowing could be explained in terms of an orienting response towards infrequent events, which errors typically are. Using a color discrimination task, we demonstrated that post-error slowing depends on the frequency of an error, not on the error information itself. Post-error slowing was observed only when errors were infrequent; when instead correct trials were infrequent, post-correct slowing was observed. Moreover, we observed similar slowing after completely irrelevant unexpected signals. We interpreted this in terms of an orienting response towards the unexpected signals that delays processing of the next stimulus. In a follow-up study, we demonstrated that the size of the feedback-related P3 and not the error-related or feedback-related negativity predicted the RT on the following trial. As the frontocentral P3 is generally considered as an index of orienting, this was in line with the orienting account (Nunez Castellar, Kühn, Fias, & Notebaert, 2010) Dissociating conflict from error adaptation Both on the basis of adaptation by binding (conflict adaptation) and the orienting account (error adaptation), a dissociation between

3 214 W. Notebaert, T. Verguts / Acta Psychologica 136 (2011) conflict and error adaptation is predicted. The adaptation by binding account states that active associations will be strengthened when conflict is detected. This principle leads to increased control after correct (incompatible) trials but does not necessarily improve performance after incorrect trials. Indeed, in incorrect trials, incorrect stimulus response representations are presumably more active than correct representations, so their associations will be strengthened, leading to worse performance. We assume that binding also operates after errors, it is only very hard to deduce which were the active representations. Most likely, there is a lot of variability with respect to the activation patterns that lead to an error, blurring the effect of binding after errors. Also on the basis of the orienting account, a dissociation is predicted. If post-error slowing is caused by the detection of an unexpected event which triggers an orienting response towards this event and delays subsequent stimulus processing, it should not matter what task follows this period of distraction. More specifically, the orienting account predicts that post-error slowing should not be taskspecific, meaning that an error in Task 1 should result in post-error slowing in the subsequent Task 2. We therefore predict that posterror slowing is not task-specific and should occur for any sequence of tasks. In order to investigate this prediction, we measured post-error slowing in data (Notebaert & Verguts, 2008) where we reported across-task conflict adaptation when both tasks shared the relevant dimension, and no such effect when they did not. In contrast to conflict adaptation, we predict post-error slowing in both conditions. Moreover, on the basis of the orienting account, we also predict that the size of post-error slowing will be related to the accuracy level of each participant, in the sense that participants who make more errors will be less surprised by an error. In particular, we predict a negative correlation between error percentage and post-error slowing. 2. Method 2.1. Participants Forty-six volunteers (age between 18 and 24; 33 females) participated and received 5 Euro for half an hour session. They were randomly assigned to condition SAME or condition DIFFERENT Procedure In condition SAME, the relevant information of Simon and SNARC trials was identical: Participants always responded to the orientation of the stimuli. The numbers 1, 2, 8, and 9 were presented centrally (SNARC trials), or an X was presented to the left or right of fixation (Simon trials). The stimuli were presented upright or in italic (tilted 20 to the right). This resulted in 12 stimuli; 1, 2, 8, 9, X left of fixation, and X right of fixation, each presented either upright or italic. Half of the participants responded with the left response key to italic stimuli and with the right response key to upright stimuli. This mapping rule was reversed for the other participants. In condition DIFFERENT, participants responded to the orientation of the number but responded to the color of the X's (numbers were always presented in black). Half of the participants pressed the left response key when a green X appeared and the right response key when a red X appeared. This mapping rule was reversed for the other half of the participants. In Simon trials stimuli were always presented upright. The stimuli were 2.8 cm by 1.4 cm. From an average viewing distance of 50 cm, this resulted in a visual angle of 3.2 by 1.6. Stimuli were presented on Pentium computers using E-prime software and response box. In each condition, each block contained 160 trials, 80 Simon and 80 SNARC trials, randomly selected with an equal number of congruent and incongruent trials. Five blocks of trials were presented. There was no practice block and participants were explicitly told so. The response stimulus interval was 800 ms, during which a central fixation cross appeared. Stimuli were presented until a response key was pressed, with a maximum response window of 5 s. 3. Results We first summarize the conflict adaptation effects (Notebaert & Verguts, 2008). In Fig. 1, we present the conflict adaptation effects that were observed for task repetitions and task alternations in both conditions (SAME and DIFFERENT). The conflict adaptation effect is quantified as the difference in congruency effects that was observed after incongruent versus congruent trials. Fig. 1 shows that conflict adaptation for task alternations (the across-task conflict adaptation effect) was limited to the SAME condition. In the DIFFERENT condition, a significant reversed conflict adaptation effect was observed for task alternations, indicating a larger congruency effect after incongruent trials than after congruent trials. This reversed Gratton effect was also explained in terms of adaptation by binding, but is beyond the scope of this manuscript (Verguts & Notebaert, 2008). The new analysis focuses on post-error slowing. We analyzed correct median RTs with a three-way ANOVA with condition as a between-subjects factor (same different relevant information) and task sequence (task repetition or task alternation) and preceding accuracy (correct or error) as within-subjects factors. The number of errors was high enough to obtain a sufficient number of trials in all cells. In the SAME condition, the number of correct responses following errors for task repetitions was on average (range 2 26) and for task alternations (range 4 30). In the DIFFERENT condition, the number of correct responses following errors for task repetitions was on average (range 1 65) and for task alternations (range 6 69). When the analyses were restricted to participants with at least 10 trials in each cell (SAME n=18 and DIFFERENT n=16), no differences were observed in any of the statistics Reaction times Median reaction times are presented in Table 1. There is a task repetition benefit, F(1,44) =26,78, pb0.001, which interacts with condition, F(1,44) =6.46, pb0.05, caused by a larger task repetition benefit in the DIFFERENT condition. There is also a marginally significant main effect of condition, F(1,44) =3.29, p=0.08. More important, however, there is overall post-error slowing as the effect of preceding accuracy is significant, F(1,44)=38.10, pb0.001 and this does not interact with condition, F(1,44) b1, ns. Fig. 1. The left side of the figure shows post-error slowing (RT after errors RT after correct) for the same and different condition for task repetitions and alternations. The right side shows the conflict adaptation effect (compatibility effect after compatible compatibility effect after incompatible trials) for the same four conditions. Vertical bars indicate 1 standard error calculated as the standard deviation of the effect in ms over participants, divided by square root n.

4 W. Notebaert, T. Verguts / Acta Psychologica 136 (2011) Table 1 Reaction times and error rates, in brackets, after errors and after correct trials for the SAME (both tasks use the same relevant information) and DIFFERENT (both tasks use different relevant information) condition for task repetitions and alternations. When we restricted the analysis to participants with at least 10 trials in each cell, post-error slowing was again significant (F(1,32)= 54.01, pb0.001), and there was again no interaction with condition (F(1,32) b1, ns.). Also the task sequence does not affect post-error slowing, and the three-way interaction is also not significant, both Fb1, ns. Fig. 1 shows the size of the post-slowing effect (correct RT after an error correct RT after a correct trial) in the four conditions, clearly demonstrating the dissociation with conflict adaptation. The orienting account predicts that participants who make more errors will be less surprised by an error and will therefore show reduced post-error slowing. In order to test this prediction we correlated the participants' post-error slowing score with the error percentage (see Fig. 2). We observed a marginally significant negative correlation in line with the orienting account, r(46)= 0.25, pb0.10. After excluding two obvious outliners (indicated on Fig. 2), this correlation decreased to r(44) = 0.24, p= Accuracy Task repetitions Error percentages are presented between brackets in Table 1. Overall there is no effect of condition, F(1,44)b1, ns., no effect of task sequence, F(1,44) =2.81, p=0.10. We reported previously that error levels tend to increase after errors (Notebaert et al., 2009). Here, we observe exactly the same pattern, F(1,44) =4.41, pb0.05 and this does not interact with condition, F(1,44) b1, ns. Task sequence, however, interacts with previous accuracy, F(1,44) =5.64, pb0.05 and also the three-way interaction is significant, F(1,44) =5.91, pb0.05. Table 1, however, indicates that all conditions show more errors after errors than after correct trials, except in the DIFFERENT condition when the task changed. Note that this post-error accuracy increase is not significant, F(1,44) =1.92, p= General discussion Task alternations After error After correct After error After correct SAME 595 (6.19) 522 (4.53) 624 (5.25) 533 (3.51) DIFFERENT 644 (8.84) 531 (3.15) 697 (3.88) 596 (5.43) In the present paper, we described behavioral adaptation after conflict and errors in the Simon task. On the basis of recent theoretical Fig. 2. Correlation between individuals' error percentage and post-error slowing. advances in both fields, we predicted a dissociation between conflict and error adaptation. In the SAME condition where conflict adaptation transferred from one task to another, post-error slowing also transferred from one task to another (for similar results see Cho, Orr, Cohen, & Carter, 2009). Most interestingly, in the DIFFERENT condition where conflict adaptation did not transfer from one task to another, post-error slowing did, indicating that post-error slowing reflects a more general process than conflict adaptation. Moreover, we observed a modest correlation between participants' post-error slowing and their accuracy level, also in line with the orienting account Aspecific slowing after errors The aspecific slowing after errors was predicted on the basis of the orienting account. If an unexpected event captures one's attention, this will delay the processing of any following event. The correlation analysis suggests that the amount of surprise associated with errors (accuracy level) influences the amount of orienting (post-error slowing). Other error-related theories would have much more difficulties explaining this effect. In the reinforcement learning theory of Holroyd and Coles (2002); Holroyd, Yeung, Coles, and Cohen (2005) for instance, it is assumed that errors provide learning signals for the motor controllers. The mechanism that is implemented to produce post-error slowing adjusts the attentional weights to the response units and would produce only task-specific post-error slowing. Reinforcement learning could however explain the correlation between accuracy and post-error slowing. Conflict monitoring theory (Botvinick et al., 2001), on the other hand, could explain aspecific slowing effects. Although this theory describes error detection in terms of conflict, the computational implementation of error adaptation differs from conflict adaptation. While conflict adaptation is implemented by a relative activation (attention) change for relevant versus irrelevant information, adaptation after errors is implemented as a decrease in the baseline activation of the response units. This functionally reflects a decrease of the response thresholds. Although this is not specified in the theory, one could assume that this decrease is aspecific and also affects other tasks. However, post-error accuracy does not increase, which would clearly be predicted on the basis of increased response thresholds. Moreover, it is unclear how conflict monitoring theory would explain the correlation between accuracy and post-error slowing Specific adaptation after conflict In our opinion, the specificity of the conflict adaptation effect is a reflection of its underlying associative mechanism. Others have argued, instead, that conflict adaptation reflects a more global control mechanism. Freitas, Bahar, Yang, and Banai (2007) for instance demonstrated conflict adaptation from color Stroop trials (with vocal responses) to flanker trials with manual responses. Although this effect at first does not seem to be in line with the adaptation by binding account, there is one particular aspect of the procedure that deserves attention. In all tasks, the irrelevant information (the word or the flankers) was presented before the relevant information. In a sense, this information can be conceptualized as a task cue. Accordingly, when participants know the upcoming task a more proactive adaptation mechanism might come into play (Fernandez- Duque and Knight, 2008). Egner (2008) argued that there might be another factor that determines transfer from one task to another, namely the type of conflict. In our experiments, one could argue that Simon and SNARC result in a very similar conflict at the response level. Consequently, it is possible that not only the same relevant dimension is required, but also the same type of conflict.

5 216 W. Notebaert, T. Verguts / Acta Psychologica 136 (2011) Conclusion We reported error adaptation from one task to another in a condition where conflict adaptation did not. This dissociation was suggested on the basis of adaptation by binding and directly predicted by the orienting account. The dissociation argues against unitary models where conflict and errors are treated similarly. Because of the strong spatial compatibility manipulation, the Simon task has been, and will remain, instrumental in investigating these and other aspects of cognitive control. References Akçay, Ç., & Hazeltine, E. (2007). Conflict monitoring and feature overlap: Two sources of sequential modulations. Psychonomic Bulletin & Review, 14, Akçay, Ç., & Hazeltine, E. (2008). Conflict adaptation depends on task structure. Journal of Experimental Psychology: Human Perception and Performance, 34, Blais, C., Robidoux, S., Risko, E. F., & Besner, D. (2007). 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