Psychological Research (2015) 79:238–248 DOI 10.1007/s00426-014-0565-5
Conflict control in task conflict and response conflict Ami Braverman • Nachshon Meiran
Received: 17 November 2013 / Accepted: 19 March 2014 / Published online: 3 April 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Studies have suggested that conflict control can modulate conflict effects in response to differing levels of conflict context. The current study probed, in two experiments of proportion congruence, the relevance of both task conflict (between a currently relevant task and irrelevant task alternatives) and response conflict (between a currently relevant response and irrelevant response alternatives) to conflict control. In Experiment 1, proportion congruence between blocks was manipulated and in Experiment 2, proportion congruence was manipulated between items. The response conflict effect was smaller when proportion of incongruence was high, regardless if task conflict or response conflict proportions were manipulated. These findings suggest that both task conflict and response conflict are monitored but that only response conflict is being influenced by this monitoring process. Theoretical implications are discussed.
Conflict control in task conflict and response conflict It is widely assumed that a major role of cognitive control is to resolve conflict, especially between a dominant, but inappropriate tendency and a non-dominant, but appropriate tendency. Conflict effects such as Stroop (MacLeod, 1991, for review), Simon (Lu & Proctor, 1995, for review), the Flanker compatibility effect (Eriksen, 1995, for review), and the task-rule congruency effect (Meiran & A. Braverman (&) N. Meiran Department of Psychology, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel e-mail: [email protected]
N. Meiran e-mail: [email protected]
Kessler, 2008, for review) have been focal in the study of cognitive control processes. For these paradigms, the conflict is defined by the response information. This is problematic since recent findings suggest that two types of conflict can be dissociated: task conflict and response conflict (e.g., Braverman & Meiran, 2010; cf. Goldfarb & Henik, 2007). The current study probed into the effect of this differentiation on conflict control, with a special focus on the influential conflict monitoring theory by Botvinick et al. (2001). According to the conflict monitoring theory (e.g., Botvinick, Braver, Barch, Carter, & Cohen, 2001), a specialized brain system in the anterior cingulate cortex initially estimates the degree of conflict. When the level of conflict is high, this system signals other brain systems to increase their involvement in conflict resolution, making conflict control adaptive. Two well-known behavioral effects of this conflict adaptation have been used as support for this claim. The first, sequential adaptation (sometimes referred to as the Gratton effect), is the finding that following incongruent trials, conflict effects are lower than after congruent trials (Gratton, Coles, & Donchin, 1992). For illustration, take the Stroop task. In this task, a participant is required to respond to the ink color of a word and ignore the word. If the word RED is written in green, for example, then this would be an incongruent trial. If the word GREEN is written in green then this would be a congruent trial. The difference between these two conditions is the Stroop effect and this effect is generally found to be smaller following incongruent trials (i.e., in trial n - 1) as compared to following congruent trials (e.g., Kerns et al., 2004). Another finding that is taken as support for conflict monitoring and modulation is the proportion congruency effect (Logan & Zbrodoff, 1979). If one compares two blocks, a block with a high proportion of incongruent trials (and a
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low proportion of congruent trials) and a block with a low proportion of incongruent trials (and a high proportion of incongruent trials), then the conflict effect in the former block is generally smaller than in the latter block. On the surface, both of these findings are counter intuitive since the conflict effect goes down in a situation of high conflict. As mentioned above, the conflict monitoring theory explained this result by assuming that conflict is actively being controlled and that this conflict control varies according to the level of conflict that is being monitored. Specificity of conflict control One recurring issue with conflict control is the specificity of the control. The conflict monitoring theory suggests that monitoring is global since it is presumably sensitive to the general level of the conflict, regardless of conflict type. There has been evidence suggesting that conflict that is monitored can be associated to different contexts. Jacoby, Lindsay, and Hessels (2003) found that if the proportion of congruency is defined not by the proportion in a given experimental block but rather by the item, there still is a modulation of the conflict effect in the same pattern. For example, in the Stroop task, if the word RED is relatively likely to appear in incongruent trials and the word GREEN is likely to appear incongruent trials, the conflict effect is lower for the former. Crump, Gong, and Milliken (2006) further showed that stimuli presented in spatial locations, which were likely to be occupied by incongruent stimuli, showed smaller Stroop effects as compared to locations likely to be occupied by congruent trials. Note that this does not negate the idea of a global conflict control mechanism. It simply suggests that conflict control can be context specific, and that the context can be defined by locations and items rather than (or perhaps in addition to) blocks. In contrast to the global conflict control mechanism described above, there have been studies suggesting that conflict control can be more specific. Egner (2008; cf., Steinhauser & Huebner, 2009; Desmet, Fias, Hartstra, & Brass, 2011) proposed that ‘‘the effects of conflict-driven control are domain-specific and are probably mediated by multiple, independent conflict control loops that can operate in parallel’’ (p. 374).Other studies have shown that conflict can be local to a specific task. Evidence for this has been found in the task switching paradigm. In this paradigm, a participant is required to frequently switch between two (or more) different tasks (Kiesel et al., 2010; Koch, Gade, Schuch, & Philipp, 2010; Meiran, 2010; Monsell, 2003, for review). This is usually done in such a way that participants cannot predict which task will be performed in the next trial. Akc´ay and Hazeltine (2008; cf. Notebaert & Verguts, 2008; Funes, Lupia´n˜ez, & Humphreys, 2010) found sequential adaptation when the task repeated, but not
when it switched (i.e., the sequential adaptation was presumably task specific since it ‘‘carried over’’ only when the same task was performed in sequence). This pattern of results is not always found (for a discussion see Akc´ay & Hazeltine, 2008; cf. Notebaert & Verguts, 2008; Funes et al., 2010), however, relevant to the current paper is the fact that conflict control seems to be, at least at times, task specific. Another relevant suggestion regarding the specificity of control is that proportion congruence and sequential adaptation could represent two different types of control. , Funes, & Lupia´n˜ez (2013; cf. Funes et al., 2010) compared sequential adaptation and proportion congruence in a paradigm involving switching between two different conflict tasks and a proportion manipulation. When looking at sequential adaptation effects, the authors found results suggesting local conflict monitoring, as described above. However, the results concerning the proportion manipulation supported a global conflict monitoring. These authors explained their results by referring to the differentiation between reactive and proactive conflict control (e.g., Braver, 2012). Whereas reactive control relates to trial level adjustments, presumably found in sequential adaptation, proactive control relates to sustained adjustments, presumably found in the block-wise manipulations of proportion congruence. All of the above discussed studies assume some form of conflict adaptation. There are, however, researchers that suggest alternate explanations for the findings in these studies. This issue will be discussed in the ‘‘General Discussion’’. Task conflict and response conflict While many studies refer to the context specificity of conflict monitoring (i.e., the source of the conflict being monitored), there has been very little mention of different conflict types. The present work fills this gap in the literature by focusing on two types of conflicts: task conflict and response conflict. Recent studies have suggested that task conflict and response conflict are processed differently (Braverman & Meiran, 2010; cf. Goldfarb & Henik, 2007; Kalanthroff, Goldfarb, & Henik, 2012; Steinhauser & Huebner, 2009). According to these authors, response conflict is a conflict regarding what the relevant response (action) is. For, example, when driving, this might be a decision to take a left turn or a right one. A task conflict would be the decision whether to drive or, for example, go for a run. This second type of conflict theoretically takes place partly if not totally independently of the conflict regarding which specific action to execute. Many of the aforementioned conflict tasks confounded task conflict and response conflict to some degree. For example, in the Stroop task, the fact that the irrelevant information is a
word may, in itself, cue a reading task rather than the (required) color-naming task, regardless of the specific word (see Goldfarb & Henik, 2007; cf. Monsell, Taylor, & Murphy, 2001). The current study The question addressed in the present paper was whether the evaluation of conflict level is indeed non-specific as suggested by Botvinick et al. (2001) or whether conflict evaluation operates differently for different conflict types, namely task conflict and response conflict as suggested by Steinhauser and Huebner (2009, cf. Desmet et al., 2011). We manipulated task conflict and response conflict by following a similar logic to that of other conflict effects (see Kornblum, Hasbroucq, & Osman, 1990, for a review). The response conflict effect (RCE) is the difference between response incongruent conditions and response congruent conditions. The task conflict effect (TCE) is the difference between task incongruent conditions and task congruent conditions. When defined in this manner, the two conflicts are not confounded, i.e., for TCE conditions, response conflict level is held constant and vice versa for RCE conditions (see the ‘‘Method’’ sections to follow for a more detailed description of the manipulations). Two experiments were run. Experiment 1 employed a block-wise manipulation of proportion congruency, separately for task conflict and response conflict. Experiment 2 employed an item specific proportion congruency manipulation, again separately for task conflict and response conflict. We examined the influence of these manipulations on TCE and RCE. This enabled us to examine which conflict type is monitored and which is influenced by monitoring, (i.e., modulated). To manipulate both task conflict and response conflict, a cued task switching paradigm was used, in which the task is cued in each trial. The benefit of using this paradigm for our purposes is that the general level of task conflict is high,
Fig. 1 Illustration of a a trial sequence, b the targets used in the different blocks (response mapping block, bivalent block and univalent experimental block) and c examples of conditions (‘‘right’’ univalent experimental target combined with different interfering stimuli). C1 Response congruent, C2 response incongruent, C3 task congruent, C4 task incongruent
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given the frequent task switches and also the fact that the task needs to be chosen in every trial. The same is true for the general level of response conflict since participants need to make a response selection on every trial. Another major advantage of using task switching is that we were able to manipulate TCE and RCE separately such that when task conflict varied response conflict was held constant and vice versa. This was achieved using univalent target stimuli that prompt only one task and one response. This is as opposed to bivalent targets that prompt responses from two different tasks and thus prompt two different tasks; something that holds true even if the two sources of information prompt the same physical response. We did not use bivalent targets since they confound task and response conflict (see Braverman & Meiran, 2010, for detail). See Fig. 1 for an illustration of the basic paradigm used in both experiments.
Experiment 1 Manipulating proportion of congruency between blocks has produced smaller conflict effects in blocks with a high proportion of incongruent trials as compared to blocks with a small proportion of incongruent trials (Log an & Zbrodoff, 1979).In the following experiment, task conflict and response conflict were manipulated separately such that there were four types of congruency conditions (task congruent; task incongruent; response congruent; response incongruent). Participants responded to four possible univalent targets, (semicircles prompting––UP, DOWN, RIGHT and LEFT, see Fig. 1), which represented for the participants two tasks (up/down vertical and left/right horizontal). These targets were combined with irrelevant arrow stimuli that caused the four types of congruency. This design made it possible to assess TCE when the level of response conflict was held constant and to assess RCE when the level of task conflict was held constant. The irrelevant arrow stimuli were associated with task or
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response information prior to the experimental (univalent) blocks by two priming blocks, one a response mapping block and one bivalent block. In the response mapping block, an association was made between arrows and response keys by asking participants to respond to singleheaded arrows (UP; DOWN; RIGHT; LEFT). In the bivalent block, an association was made between doubleheaded arrows (up/down vertical and left/right horizontal) and tasks using these arrows as informational task cues. Keep in mind that bivalent targets prompt responses that are relevant to both tasks and therefore an informational cue is needed to prompt the relevant task in a trial. Another function of using the bivalent targets in the priming blocks was that the participants learned to perceive the stimulus response mappings in terms of two tasks rather than in terms of S–R rules (for a discussion on this issue see Dreisbach, Goschke, & Haider, 2007). Regarding the manipulation of proportion of congruence between blocks, for all participants, in 50 % of the trials, task congruency was manipulated and in the remaining 50 % of the trials, response congruency was manipulated. For one group of participants, the proportion of task congruency (congruent or incongruent) was manipulated between blocks as described shortly. For the other group of participants, the proportion of response congruency (congruent or incongruent) was manipulated as described shortly. In detail, in the group in which the proportion of response congruent trials was manipulated, in one block (high proportion incongruent block), 70 % of the relevant trials were response incongruent and 30 % of the relevant trials were response congruent. In the low proportion incongruence block, the opposite proportions were used. For this group, there was a chance of 50 % of a trial being congruent or incongruent in the trials in which task congruency was manipulated. In the group of participants for whom the proportion of task congruent trials was manipulated, there were again two different blocks. In the high proportion incongruent block, 70 % of the relevant trials were task incongruent and 30 % were task congruent. The opposite proportions were held in the low proportion incongruent block. For this group, there was a chance of 50 % of a trial being response congruent or incongruent in the trials in which response congruency was manipulated.
Apparatus and stimuli The experiment was run on a Pentium 4 computer. It was programmed and run on E-Prime 2.0 (Psychology Software Tools, Inc.). The participants responded to the stimuli on the screen by pressing assigned keys on a standard keyboard. These were the numpad buttons: 1 (used for ‘‘down’’/’’left’’) and 9 (used for ‘‘up’’/‘‘right’’) or 3 (‘‘down’’/‘‘right’’) and 7 (‘‘up’’/‘‘left’’). Participants were assigned to the two configurations randomly. Univalent targets were frames of half circles subtending a visual angle of approximately 2.86° 9 2.86°. (assuming a 60 cm viewing distance). There were four possible half circles, representing the upper, lower, left, and right part of a full circle. Bivalent targets were frames of quarter circles (6.68° 9 6.68°). There were four possible quarter circles, representing the upper-right, upper-left, lower-right, and lower-left part of a full circle. Within the bivalent targets, one of two possible double-headed arrows appeared (0.95° 9 1.62°) thus cuing specific tasks (‘‘upper/lower’’; ‘‘left/right’’). Single-headed arrows that prompted specific responses (‘‘up’’; ‘‘down’’; ‘‘left’’; ‘‘right’’) were used (0.95° 9 1.24°) in a response mapping block that helped associate the arrows with the corresponding responses. The fixation stimulus was the symbol ‘‘?’’.All stimuli appeared in the center of the screen in white, on a black background. Regarding the experimental univalent trials, if a doubleheaded arrow appeared (as irrelevant information), it could either be congruent with the expected task or incongruent with it. Single-headed arrows that appeared could either be response congruent or response incongruent with the constraint that only task relevant responses could be prompted.
Method Participants Thirty-nine Ben-Gurion University undergraduates participated in this experiment in return for course credit. All of the participants reported having normal or corrected-tonormal vision and no diagnosed learning disabilities.
Fig. 2 Example of high proportion task incongruent. For Experiment 1, this is an example of a block and its associated congruency proportions. For Experiment 2, this is an example of a target and its associated congruency proportions
In other words, if the task was right–left for example, only the right pointing or the left pointing arrows could appear as single-headed arrows (i.e., task conflict level was held constant). These four possible conditions (for every possible univalent target) were manipulated with regards to proportion as previously described (see Fig. 2 for an example). Procedure There were two cycles of blocks, each including a response mapping block (60 trials) in which participants reacted to the single-headed arrows, a bivalent block (60 trials), in which participants reacted to bivalent targets and thus had to use the double-headed arrows as task cues, and a univalent, experimental block (176 trials), in this order. The response mapping block and the bivalent blocks were not analyzed and were only introduced to ensure that participants associate the arrows with their respective responses or tasks. Participants were instructed to respond as quickly and as accurately as possible. They were further informed that the instruction screens also represented break time. For the response mapping blocks, in each trial, one of the single-headed arrows appeared and participants had to press the corresponding key, indicating the arrow direction. For the bivalent blocks, the target stimuli were the quarter circles and the responses indicated UP vs. DOWN or RIGHT vs. LEFT, depending on which task was cued. Notice that the target stimulus was uninformative regarding which task was required, making it necessary to process the task cues (the double-headed arrows). Thus, the bivalent blocks forced participants to associate the double-headed arrows with their respective tasks. For the univalent blocks, the experimental blocks, the participants were instructed again to indicate UP, DOWN, RIGHT, and LEFT, but this time there was no need to get a task cue given the univalent nature of the targets. Within the univalent targets, there was an ‘‘interference’’ stimulus, which came in the form of one of the single-headed arrows, used in the response-mapping blocks, or one of the double-headed arrows, used as cues in the bivalent blocks. Participants were instructed to attend to the location in which the arrow was presented but to ignore its shape. According to the configuration of the arrows and the targets, the trials could belong to one of four relevant congruency conditions: task congruent; task incongruent; response congruent; response incongruent (see Fig. 1). The proportion of congruency conditions was as described above (see Fig. 2 for an example of proportions for one participant). For all blocks, there was a chance of 50 % of a trial being a switch trial (different task from the previous task) or repeat trial (same task as the previous task) an equal chance of any one of the targets to appear
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and an equal chance of any specific interference stimulus to appear within the univalent targets. The sequence of events in a trial consisted of a fixation (500 ms) then a target stimulus (simultaneously accompanied by a task cue if the target was bivalent or accompanied by an interference stimulus if the target was univalent) presented until the response was given and then a blank screen (500 ms) presented until the beginning of the next trial. The participants were randomly assigned to group and the order of experimental blocks (i.e., first high proportion incongruent, then low proportion incongruent or vice versa) was set randomly between participants [in addition to the random setting of response mappings (2) as described above).This made for eight possible configurations that participants were assigned to. The experimental session lasted approximately 30 min. Results and discussion We ran two independent sets of analyses of variance (ANOVAs), one on TCE and the other on RCE. Each set of ANOVAs had a factorial design of proportion incongruent (high; low) 9 conflict proportion manipulated (task; response, between subjects) 9 congruency (congruent; incongruent). The congruency factor was defined differently in the two analyses. In one analysis (TCE), these were task congruent vs. task incongruent trials. In the other analysis (RCE), these were response congruent vs. response incongruent trials. One participant’s data were removed from the analysis because of an exceptionally high error rate (0.12) as compared to the rest of the participants (mean = 0.03; SD = 0.02).Only the univalent experimental blocks were analyzed and the first 16 trials of each block were removed. Trials with errors, trials following errors and trials with an exceptionally slow (more than 3,500 ms) reaction time (RT) were removed (resulting in 5.68 % trials removed). Descriptive statistics are shown in Table 1. TCE analyses The only significant effect in the RT analysis was a main effect for task congruence (18 ms) such that task incongruent trials (560 ms) were slower than task congruent trials (542 ms), F(1, 36) = 7.27, p \ 0.02, g2p = 0.17, thus indicating a significant TCE effect. There were no significant effects for error rates. RCE analyses In the RT analysis, there was a significant main effect for response congruence (38 ms) such that response incongruent trials (577 ms) were slower than response congruent
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Table 1 Conflict proportion manipulated 9 proportion incongruent 9 congruence (RCE/TCE) for Experiments 1 and 2 Response
RCE Congruent Incongruent
520 500 480 460
Values are in ms. Values in parenthesis are error rates
trials (539 ms), F(1,36) = 12.68, p \ 0.01, g2p = 0.26, thus indicating a significant RCE. There was a significant interaction between RCE and proportion incongruent, F(1, 36) = 7.42, p \ 0.01, g2p = 0.17 (see Fig. 3). Follow-up contrasts revealed a significant RCE when proportion incongruent was low, F(1, 36) = 26.21, p \ 0.01, and a non-significant RCE when proportion incongruent was high, F(1, 36) = 0.74, p [ 0.40. In the error rates analysis, there was a significant main effect for response congruence (0.02) such that response incongruent trials (0.04) showed more errors than response congruent trials (0.02), F(1, 36) = 6.28, p \ 0.02, g2p = 0.15. RCE and TCE were both significant. The most important findings were (a) that RCE was smaller in blocks with a high proportion of incongruent trials (regardless of whether what has been manipulated was the proportion of task incongruent trials or the proportion of response incongruent trials), and (b) that TCE was unaffected by proportion congruence. The fact that RCE was influenced by proportion of task congruent/incongruent trials is a novel finding. The present results already suggest a distinction between (a) the level at which conflict is being monitored on the one hand and (b) the level which is being influenced by conflict monitoring (i.e., modulated). Here, it seems as if both task conflict levels and response conflict levels are monitored but that conflict monitoring is influencing only response conflict. It is important to note that despite the fact that sequential adaptation and proportion congruence have often been differentiated (see above), it is possible that at times,
High Proportion Incongruent
Fig. 3 Mean reaction time (RT in ms) according to proportion incongruent and response conflict: Experiment 1
proportion congruence is actually a case of sequential adaptation. This is because if one raises the proportion of incongruent trials in a block, one also raises the proportion of incongruent trials that precede the current trial, something that could theoretically account for the proportion congruency effects found (Schmidt, 2013). To show that the RCE was influenced by the proportion congruence context, rather than by some repetition effect, we adopted another contextual manipulation in Experiment 2 that is not open to these and similar criticisms.
Experiment 2 Proportion congruence manipulations have the problem of confounded stimulus repetition effects, because when most of the trials are, say, response congruent, most of the trials are also following a response congruent trial (Schmidt, 2013, for review). Fortunately, Jacoby et al. (2003) showed similar effects when the proportion manipulation was tied to specific items instead of being tied to the block. With such manipulation, sequential effects are no longer an issue. Therefore, in this experiment, proportion congruence was manipulated between items and not between blocks while keeping the proportion of in/congruent trials constant throughout the univalent blocks. Specifically, stimuli for one task were used to manipulate proportion congruence of task conflict, whereas those of the other task were used to manipulate proportion congruence of response conflict. The manipulation went as follows. For both tasks, in half of the trials, task congruence was manipulated and in the
other half of the trials, response congruence was manipulated. For one task (e.g., the up–down task),in the 50 % of the trials in which task congruence was manipulated, 70 % were incongruent and 30 % congruent for one target (e.g., ‘‘left’’ stimuli; high proportion incongruent) and the opposite proportion was held for the other target of the task (e.g., ‘‘right’’ target; low proportion incongruent). For this task, there was a chance of 50 % of a trial being congruent or incongruent in the remaining 50 % of the trials in which response congruence was manipulated. In the second task (e.g., the left–right task, accordingly), in the 50 % of the trials in which response congruence was manipulated, 70 % were incongruent and 30 % congruent for one target (e.g., ‘‘upper’’ targets; high proportion incongruent) and the opposite proportion for the other target of the task (e.g., ‘‘lower’’ targets; low proportion incongruent). For this task, there was a chance of 50 % of a trial being congruent or incongruent in the other 50 % of the trials in which task congruence was manipulated. Note that, the proportion congruence remained the same for all the univalent blocks. Method Participants There were 39 participants who participated in a 40-minute long session in return for 35 NIS (approximately $9). Procedure The experimental design and the stimuli were identical to Experiment 1 except for the following changes. There were three cycles of blocks. The four proportion congruence conditions were affixed to target stimuli in the univalent blocks. For one target (within a task), there was a high proportion of task incongruent trials, and for the second target in that task, there was a low proportion of task incongruent trials. For both these targets, response congruency had a 50 % chance of a trial being congruent or incongruent. Similarly for the other task, one target had a high proportion of response incongruent trials and the second target of that task had a low proportion of response incongruent trials. For both these targets, task congruency had a 50 % chance of a trial being congruent or incongruent (see Fig. 2 for an example of proportions for one target). Other than this, the blocks were identical. Note that the other block types (e.g., bivalent) were identical to those of Experiment 1. All the possible combinations (8) of associating univalent targets with congruency proportion manipulations in addition to the two combinations of response mappings (as described in ‘‘Experiment 1’’) made for 16 possible configurations which participants were assigned randomly.
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Results and discussion The analytic design and the data removal criteria were the same as in Experiment 1 (resulting in 6.76 % removed trials). Descriptive statistics are shown in Table 1. TCE analyses The only significant effect in the RT analysis was a main effect for task congruence (21 ms) such that task incongruent trials (519 ms) were slower than task congruent trials (498 ms), F(1, 38) = 16.94, p \ 0.01, g2p = 0.31, indicating a significant TCE. There were no significant effects for error rates. RCE analyses In the RT analysis, there was a significant main effect for response congruence (42 ms) such that response incongruent trials (589 ms) were slower than response congruent trials (547 ms), F(1, 38) = 30.08, p \ 0.01, g2p = 0.44, indicating a significant RCE. There was an unpredicted significant interaction between proportion incongruent and conflict proportion manipulated, F(1, 38) = 5.52, p \ 0.03, g2p = 0.13. Follow-up contrasts revealed that when conflict proportion manipulated was task, RT was non-significantly slower when proportion incongruence was high (518 ms) as compared to low (508), F(1, 38) = 1.60, p \ 0.22, whereas when conflict proportion manipulated was response, RT was significantly faster when proportion incongruence was high (505 ms) as compared to low (523), F(1, 38) = 6.91, p \ 0.02. In the analysis of the error rates, there was a significant main effect for response congruence (0.02) such that response incongruent trials (0.04) had more errors than response congruent trials (0.02), F(1, 38) = 6.30, p \ 0.02, g2p = 0.14. Importantly, there was a significant interaction between response conflict and proportion incongruence, F(1, 38) = 5.54, p \ 0.03, g2p = 0.13 (see Fig. 4). Follow-up contrasts revealed a significant proportion of errors (PE)–RCE when proportion incongruence was low, F(1, 38) = 9.59, p \ 0.01, and a non-significant PE–RCE when proportion incongruence was high, F(1, 38) = 0.84, p = 0.36. TCE and RCE were again both significant. RCE was again smaller (significantly for error data) in blocks with a high proportion incongruence (regardless if the conflict proportion manipulated, task or response). TCE was again unaffected by proportion incongruence. This experiment showed a similar result (albeit in errors) to that found in Experiment 1, thus ruling out sequential modulation as a confound. It seems that there is a generally
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RCE Congruent Incongruent
0.06 0.05 0.04 0.03 0.02 0.01 0.00 Low
Fig. 4 Proportion of errors according to proportion incongruent and response conflict: Experiment 2
more controlled strategy when in situations of high conflict. There is a slowing during response congruent trials and/or a speeding during response incongruent trials (this is in high proportion incongruent conditions as compared to low proportion incongruent). Another interesting finding in the present experiment concerns the ability to validate TCE as being a different phenomenon than RCE. Specifically, one could argue that response selection involves four abstract responses, UP, DOWN, RIGHT, and LEFT, one of which is chosen. Once the response is chosen, it is mapped to its key using constant links (e.g., Schneider & Logan, 2005). With this model in mind, let us consider (without loss of generality) the UP target. If this target is response congruent, it is accompanied by an UP arrow. If, however, this is a task congruent trial, the double-headed arrow prompts both UP and DOWN. One would therefore expect the task congruent condition to yield slower response than the response congruent trial. The means are in the opposite-to-predicted direction. Specifically, response congruent trials (547 ms) yielded slower responses than task congruent trials (498 ms), and even than task incongruent trials (519 ms). Thus, it is difficult to see how a model working in this manner could account for the results. A more plausible model would assume that task conflict and response conflict affect different processes, at least partially.
as ‘‘transition effect’’). This is the difference between a task switch trial and a task repeat trial. Specifically, Braverman and Meiran (2010); cf. Kalanthroff and Henik (2013)), found, in their second experiment, an interaction between transition and task conflict, such that TCE was smaller during switch trials as compared to repeat trials. For the current analyses, we re-ran all of the analyses from the two experiments and also included the transition variable. The main effects for transition are shown in Table 2, showing that we found switch costs in the experiments. In Experiment 1, there were no significant interactions in the RT data, but there was an interaction in the error data. Specifically, a significant triple interaction between transition, RCE and proportion incongruence was found, F(1, 36) = 4.36, p \ 0.05, g2p = 0.12 (see Table 3). For Experiment 2, there was a significant interaction between transition and conflict proportion manipulated, F(1, 38) = 4.11, p \ 0.05, g2p = 0.10, such that there was no switching cost when proportion response congruency was manipulated and a positive (0.02) switch cost when proportion task congruency was manipulated. In summary, with regards to transition, the results from the present experiments, joined with those in previous experiments (Braverman & Meiran, 2010; cf. Kalanthroff Table 2 Main effects of transition for Experiments 1 and 2 Repeat
502 (0.03) 493 (0.03)
527 (0.04) 526 (0.04)
25.65 (4.34) 80.01 (6.95)
\0.01 (\0.05) \0.01 (\0.02)
Experiment 2 RCE analysis TCE analysis
Values are in ms. Values in parenthesis are error rates
Table 3 Transition 9 proportion incongruent 9 congruence (RCE) for Experiment 1 Repeat
Low prop incong
High prop incong
Low prop incong
High prop incong
Transition analyses One of the more common measurements used in the task switching paradigm is switch cost (sometimes referred to
Values are in error rates
&Henik, 2013) suggest a complex, and not overly stable pattern that may be studied in the future.
General discussion In the present paper, we examined the interrelationship between task conflict and response conflict, particularly in relation to conflict context. The most novel aspect of the current paradigm was that task conflict and response conflict were not confounded with each other. When task conflict was manipulated, response conflict was held constant and vice versa. The results showed significant TCE and RCE in both experiments. In these experiments, we manipulated proportion congruence of task conflict and response conflict. In Experiment 1, there were blocks with a high/low proportion of task/response congruent/incongruent trials. In Experiment 2, there were target items associated with a high/low proportion of task/response congruent/incongruent trials. In both experiments, we found that a high proportion of incongruent trials (regardless of congruency type) resulted in a smaller RCE, as compared to low proportion of incongruent trials. This held true for RT in Experiment 1 and in PE in Experiment 2. TCE, on the other hand, did not seem to be modulated by proportion incongruence.
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lack of modulation of TCE was due to a power problem. An aspect of the design of the experiments that may be relevant to this issue is the differential utility of response and task-related information. Specifically, response conflict theoretically had to be resolved to select a response, whereas being univalent trials, the task conflict did not need to be resolved to select a response. This aspect of the design could explain the smaller TCE. Note that despite this discrepancy between conflict types, TCE was significant. Moreover, the core result cannot be accounted for the lower statistical power presumably associated with TCE because task congruence proportion manipulation influenced the RCE as strongly as did the response congruence proportion manipulation (i.e., the triple interaction was not significant). If TCE-related manipulations were really less ‘‘powerful’’ than RCE-related manipulations then one would expect a significant triple interaction. One potential criticism of the current study is that the design was very specific and it is not fully clear whether the conclusions could generalize to other conflict tasks. Specifically, it is not clear that a task decision is a very prominent selection process in other conflict tasks. One thing that does seem clear is that a task decision process does exist and that in this case, where task decisions are frequent, varying levels of task conflict seem to modulate response conflict in a similar fashion to varying levels of response conflict.
Immediate implications Conflict control vs. contingency effects The first immediate implication is that there were both TCE and RCE and that these effects were dissociable as seen by the fact that while both conflicts were monitored, only response conflict was modulated by proportion congruence. These findings extend previous findings (Braverman & Meiran, 2010; cf. Goldfarb & Henik, 2007; Steinhauser & Huebner, 2009) who showed evidence for TCE but, however, did not show that it is distinct from RCE. The second immediate implication concerns the distinction between the monitored level and the level being influenced by monitoring. Our results show that while the RCE was influenced by proportion congruence, the TCE was never influenced by it. We interpret this finding as suggesting that the conflict levels of both conflict types are monitored but that only RCE is being influenced by the monitored conflict level while TCE is not being visibly influenced by it. If true, our conclusion is consistent with the idea concerning a global monitoring system that modulates only specific conflict types. Potential limitations One finding is that TCE seemed to be consistently smaller than RCE, something that raises the question whether the
Schmidt (2013) reviewed alternate explanations to many proportion congruent related findings which are taken to support conflict control. These explanations are based on the fact that, when conflict proportions are being manipulated, this leads to a change in task contingencies that, in themselves, could have produced the results. Can this be true regarding the present results? We do not think so. As explained in detail in the ‘‘Appendix’’, when response conflict proportion was manipulated, the interfering arrows did not predict any specific response. Therefore, it could not have modulated the RCE. When task conflict proportion was manipulated, the interfering arrow did predict a specific response. Hence, this manipulation should have modulated TCE and not RCE, whereas in fact it influenced RCE and not TCE, just the opposite-to-predicted. Wider theoretical implications The current results provide an important constraint to current theories. A dominant theory by Botvinick et al. (2001) suggests a domain-general conflict monitoring system. This model could explain the results by assuming that both task conflict and response conflict are monitored
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in the domain-general system. To explain the current results, the model must assume that the domain-general system is capable of modulating response conflicts but not task conflicts. The model must also assume that task conflict is also monitored. Other models suggest that monitoring is domain-specific. Akc´ay and Hazeltine 2008; (cf. Crump et al., 2006; Notebaert & Verguts, 2008) considered conflict to be local, such that if a task is conflicting then conflict modulation is specific to that task. These models cannot explain the current results because they describe both the monitoring and the modulation of response conflict as being specific to a given task/context. However, we found that the modulation occurred across tasks, but was conflict-type dependent. This is seen in several aspects in our results. First and foremost, transition did not systematically modulate the results. Moreover, in Experiment 1, the proportion manipulation was not item (and thus, task) specific, but was done across tasks and at the level of the block. Moreover, as currently formulated, the models do not distinguish between task conflict and response conflict and thus we do not see how their current formulation could account for the dissociation. These models, too, must be adjusted to account for the present results. Egner (2008) proposed multiple, domain-specific conflict control mechanisms, specifically a response level conflict control and a stimulus level conflict control. Nonetheless, this model, as currently framed, does not predict the results found here. The idea concerning multiple, domain-specific conflict control mechanisms with regards to task conflict and response conflict is a promising one if one assumes that separate mechanisms for task conflict and response conflict. This model, however, does not explain the interplay found between the two mechanisms and therefore would need to adapt to explain the current findings.
Appendix The purpose of the Appendix is to describe the proofs of why response repetition could not explain the conflict adaptation results found in Experiment 2. Without loss of generality, let us consider just the item proportion manipulation (Experiment 2) and the UP–DOWN task in a particular configuration of the experiment. Response congruence manipulation When the UP target stimulus is mostly response congruent, : appears in 35 % of the trials and ; appears in 15 % when the correct response is UP. In this case, the DOWN target stimulus will be mostly response incongruent, so that : appears in 35 % and ; appears in 15 % when the correct response is DOWN. Note that, for the UP–DOWN task, the
proportions are the same for both UP and DOWN target stimuli and ; is more frequent than :. Consequently, the arrows are completely uninformative with respect to the correct response. The arrows do prime a specific response (: is more frequent than ;, but regardless of proportion congruency). Moreover, since participants were assigned to different task configurations in a random order, there was no systematic higher proportion of a given arrow across participants. Task conflict manipulation When the UP target stimulus is mostly task congruent, l appears in 35 % of the trials and $ appears in 15 % when the correct response is UP. In this case, the DOWN target stimulus is mostly task incongruent, so that $ appears in 35 % and l appears in 15 % when the correct response is DOWN. Note that, for the UP–DOWN task l appears more often when the correct response is UP and $ appears more often when the correct response is DOWN. Therefore, the interfering arrows do predict the correct response in this case. Note that when the proportion of task conflict was manipulated for UP and DOWN, the proportion of response conflict was 25:25 for these targets. The single-headed arrows serving to produce RCE were uninformative. Hence, RCE should have been unaffected, but it was affected. Moreover, in this case TCE should have been affected, but it was not. Note that, in this case, the proportion manipulation should have influenced TCE, but it did not.
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