626 BOTVINICK BRAVER BARCH CARTER AND COHEN Sitton 1998:Treisman 1988).It also inf that po ah the Part 1:Cognitive Neuroscientific Evidence for the ams whil Detection of Conflict off oth et al. 1980 Anterior Cingulate Cortex idea ans er to the question of how a need for incre ased control migh aiedadja ous callosum on the ater 9gnrol(e.g,D'Esposioct 5;LaBerge,1990 conflict itself. laim ho ver.noc sing.ACC Using Conflict as a Basis for Modulating Control engagement ha een reported in a volve nguage.leamning and me ceptual ta et de The potential usefulne of conflict as a hasis for th nd dua mong of cont on. &N oski C Westbury.1).making it dificult to discemm aning ments in perceptual selection.which intu serve toalleviate ensup a new In the vears since Berlyne (1960)made this sugge ty he for th stion the from ACC activ idea tha AC highly theory-driven wor For mple,the production system n the ar (Lai om 0871 by the ses. one imp rta nt class of which ibleesco ween sim usly selecte s using f specific tasks drawn fro appears to play a similar role in the theory of contro here as simulation study 1 test the consisteney of our h m(SAS)is u 198 ing the pro ang ac on pro n these th sesby whichaction schemasare routinely selected ugh the theors what Cognitive Activation of the ACC:Review of Major Findings flict a peee an the role of the ACC in ion hae hee Th using a variety of meth ng s are not 999 199995Ni&Wa This the work nab 1979).and brain ation techniques ncluding functiona work within wh module regulates the iological data have inspire some infl input from ot A 100 conflict occurs between mes sages converging on a single n most of this earlie work. conflic monitor has beer ed tific Mo its mot e st we wil almost entirely theoretica conflict mo o of the po oring has be ty in rather than be cause of expe part of a more d tior the AC e 626 BOTVINICK, BRAVER, BARCH, CARTER, AND COHEN been portrayed as helping to prevent the interference that can occur when multiple objects are processed in parallel (e.g., Mozer & Sitton, 1998; Treisman, 1988). It also informs accounts that por￾tray attention as serving to regulate the flow of information through the processing system, favoring flow into selected pro￾cessing streams while helping to gate off others (Cohen et al., 1990; Desimone & Duncan, 1995; Norman & Shallice, 1986). The idea that control serves to prevent conflicts suggests one answer to the question of how a need for increased control might manifest itself in the processing system. It implies that a need for greater control will typically be indicated by the occurrence of conflict itself. Using Conflict as a Basis for Modulating Control The potential usefulness of conflict as a basis for the regulation of control was recognized early on by Berlyne (e.g., 1960). Work￾ing within an information-theoretic framework, Berlyne proposed that the occurrence of conflict often leads to compensatory adjust￾ments in perceptual selection, which in turn serve to alleviate conflict. In the years since Berlyne (1960) made this suggestion, the idea that conflict might be linked to the regulation of cognitive control has resurfaced intermittently, usually in the context of highly theory-driven work. For example, the production system architecture known as Soar (Laird, Newell, & Rosenbloom, 1987) proposes that problem-solving algorithms are triggered by the occurrence of impasses, one important class of which involves conflicts between simultaneously selected but incom￾patible productions. Conflict appears to play a similar role in the theory of control put forth by Norman and Shallice (1986). Here, a supervisory attentional system (SAS) is understood as monitoring the pro￾cesses by which action schemas are routinely selected, intervening when these contention-scheduling processes prove inadequate. Al￾though the theory does not explicitly indicate what particular events within contention scheduling serve to trigger SAS interven￾tion, it is emphasized that contention scheduling serves primarily to prevent conflict among potentially relevant schemas (Norman & Shallice, 1986). Thus, the theory seems to imply that control is recruited when conflicts occur that contention-scheduling pro￾cesses are not able to resolve efficiently. A more explicit instance is provided by the work of Schneider and Detweiler (1987, 1988). This specifies a connectionist-control framework within which a central control module regulates the exchange of information among a number of domain-specific processing modules. In this scheme, input from control is recruited when conflict occurs between messages converging on a single module. In most of this earlier work, conflict monitoring has been adopted as a background assumption, rather than a direct object of scientific inquiry. Moreover, its motivation has typically been almost entirely theoretical; conflict monitoring has been incorporated primarily because it makes sense or because it solves computational problems, rather than because of experi￾mental evidence pointing to its occurrence. However, recent work from cognitive neuroscience has begun to provide evi￾dence that conflict monitoring may in fact play a role in human cognition. Specifically, this work indicates that the occurrence of conflict may trigger activation in a specific area of the brain, the ACC. Part 1: Cognitive Neuroscientific Evidence for the Detection of Conflict Anterior Cingulate Cortex The ACC, situated adjacent to the corpus callosum on the medial surface of the frontal lobe,' is widely believed to play a role in cognitive control (e.g., D'Esposito et al., 1995; LaBerge, 1990; Mesulam, 1981; Posner & DiGirolamo, 1998). Beyond this general claim, however, no consensus exists as to its specific contribution to cognitive processing. ACC engagement has been reported in a remarkably wide variety of cognitive settings, including tasks that involve language, learning and memory, perceptual target detec￾tion, imagery, motor control, and dual-task performance, among other capacities (Cabeza & Nyberg, 1997; Paus, Koski, Carama￾nos, & Westbury, 1998), making it difficult to discern a meaning￾ful common factor that might explain ACC engagement across studies. The notion of conflict monitoring opens up a new possi￾bility here, for the vast majority of data from ACC activation studies appears consistent with the idea that the ACC responds to the occurrence of conflict.2 In the following section, we present an overview of ACC activation studies, dividing them into three categories and suggest￾ing how ACC activation in each of these can be interpreted as reflecting a response to the presence of conflict. In order to make this idea explicit and support its validity, we conducted computer simulations using models of specific tasks drawn from each of the three basic areas of the ACC literature. These studies, presented here as Simulation Study 1, test the consistency of our hypotheses with existing accounts of information processing in these three domains, applying a quantitative measure of conflict to simulate findings from the ACC activation literature. Cognitive Activation of the ACC: Review of Major Findings Empirical research on the role of the ACC in cognition has been conducted using a variety of methodologies, including neuropsy￾chological techniques (e.g., Janer & Pardo, 1991; Turken & Swick, 1999), single-unit recording (e.g., Gabriel, 1993; Niki & Wa￾tanabe, 1979), and brain activation techniques including functional neuroimaging and event-related potentials. Although neuropsy￾chological and neurophysiological data have inspired some influ￾ential theories of ACC function (e.g., Mesulam, 1981; Vogt, Finch, & Olson, 1992), the vast majority of recent findings and some of 1 Anatomically, the anterior cingulate cortex begins above the callosum, extending forward to wrap around the genu and end inferiorly to it. However, the vast majority of the studies with which we will be concerned involve activation of the portion of the ACC posterior to the genu and superior to the callosum (cf. Bush et al., 1998; Paus et al., 1998, for discussions of functional heterogeneity in the human ACC). 2 As specified in the general discussion, the idea that the ACC responds to conflict is here viewed as part of a more general monitoring function, according to which the ACC responds to a variety of events, all indicating that attentional adjustments are needed to optimize performance or avoid negative outcomes