The conflict monitoring account posits that globally high levels of conflict trigger engagement of top-down control; however, recent findings point to the mercurial nature of top-down control in high conflict contexts. The current study examined the potential moderating effect of associative learning on conflict-triggered top-down control engagement by testing the Associations as Antagonists to Top-Down Control (AATC) hypothesis. In 4 experiments, list-wide proportion congruence was manipulated, and conflict-triggered top-down control engagement was examined by comparing interference for 50% congruent items across mostly congruent (low conflict) and mostly incongruent (high conflict) lists. Despite the fact that global levels of conflict were varied identically across experiments, evidence of conflict-triggered top-down control engagement was selective to those experiments in which responses could not be predicted on the majority of trials via simple associative learning, consistent with the AATC hypothesis. In a fifth experiment, older adults showed no evidence of top-down control engagement under conditions in which young adults did, a finding that refined the interpretation of the patterns observed in the prior experiments. Collectively, these findings suggest that top-down control engagement in high conflict contexts is neither the default mode nor an unused (or non-existent) strategy. Top-down control is best characterized as a last resort that is engaged when reliance on one’s environment, and in particular associative responding, is unproductive for achieving task goals.

The item-specific proportion congruency (ISPC) effect is the finding of attenuated interference for mostly incongruent as compared to mostly congruent items. A debate in the Stroop literature concerns the mechanisms underlying this effect. Noting a confound between proportion congruency and contingency, Schmidt and Besner (2008) suggested that ISPC effects are entirely contingency based. We introduce a broader theoretical analysis that points to the contribution of both contingency and item-specific control mechanisms. Our analysis highlights that proportion congruency is not confounded with contingency when the relevant dimension functions as the ISPC signal, and predicts that evidence of item-specific control should be obtained by shifting the signal from the irrelevant to the relevant dimension. We examine this prediction in a picture-word Stroop paradigm. When the relevant dimension functions as the ISPC signal (Experiments 1 and 2), evidence of control is obtained. When the irrelevant dimension functions as the ISPC signal (Experiment 3), contingencies can account for the ISPC effect. These patterns support our theoretical analysis, challenge a pure contingency account, and favor the inclusion of control in accounts of ISPC effects.

Cognitive control is by now a large umbrella term referring collectively to multiple processes that plan and coordinate actions to meet task goals. A common feature of paradigms that engage cognitive control is the task requirement to select relevant information despite a habitual tendency (or bias) to select goal-irrelevant information. At least since the 1970s, researchers have employed proportion congruent (PC) manipulations to experimentally establish selection biases and evaluate the mechanisms used to control attention. PC manipulations vary the frequency with which irrelevant information conflicts (i.e., is incongruent) with relevant information. The purpose of this review is to summarize the growing body of literature on PC effects across selective attention paradigms, beginning first with Stroop, and then describing parallel effects in flanker and task-switching paradigms. The review chronologically tracks the expansion of the PC manipulation from its initial implementation at the list-wide level, to more recent implementations at the item-specific and context-specific levels. An important theoretical aim is demonstrating that PC effects at different levels (e.g., list-wide vs. item or context-specific) support a distinction between voluntary forms of cognitive control, which operate based on anticipatory information, and relatively automatic or reflexive forms of cognitive control, which are rapidly triggered by the processing of particular stimuli or stimulus features. A further aim is to highlight those PC manipulations that allow researchers to dissociate stimulus-driven control from other stimulus-driven processes (e.g., S-R responding; episodic retrieval). We conclude by discussing the utility of PC manipulations for exploring the distinction between voluntary control and stimulus-driven control in other relevant paradigms.

1484The Stroop color-naming task (Stroop, 1935) is well suited for evaluating flexibility in the control of cognitive processes and behavior. In the congruent condition of the task, stimulus word matches stimulus color (e.g., BLUE in blue ink) and participants may rely on well-learned reading processes to produce fast and accurate responding. In the incongruent condition, in contrast, accurate responding requires participants to use cognitive control mechanisms to dampen word reading and activate color-naming processes. The additional time that is taken to name the ink color in the incongruent relative to the congruent condition is referred to as Stroop interference. Although the task might seem relatively simple, the literature is replete with reports of robust Stroop interference effects (for a review, see MacLeod, 1991). Close to 1,000 articles have been published on the topic, yet the control mechanism(s) used to dampen word reading and activate color-naming processes remain to be fully explicated.A complicating (or revealing, as we will argue) factor is the different instantiations (e.g., blocked conditions vs. intermixed trials) of the Stroop color-naming task appearing in the literature. Different task contexts appear to elicit different forms of cognitive control, precluding a unitary account of control mechanisms. Proportion congruence is one prominent factor that influences the control mechanisms that are adopted within a given task. Traditionally, proportion congruence is manipulated at a list-wide level by disproportionately presenting congruent and incongruent trials within a list. Participants can use frequencies to predict what type of trial is most likely to occur next, and control processes can be biased toward (as in a mostly congruent list) or away from (as in a mostly incongruent list) word reading prior to stimulus onset on the basis of these expectancies. Such contexts seem to induce a preparatory, goal-driven control mechanism that is implemented in a sustained fashion across trials (i.e., the bias toward or away from word reading remains constant throughout a list), analogous to the proactive control mechanism recently posited in the dual-mechanisms-of-control account (Braver, Gray, & Burgess, 2007). In contrast, in other task contexts, congruent and incongruent trials occur equally often within a list, and one is unable to anticipate the upcoming trial type and prepare control processes accordingly. These contexts demand a more flexible control mechanism that is capable of modulating word-reading and color-naming processes in a transient fashion on a trial-by-trial basis. Because such modulation occurs after stimulus onset, such a control mechanism must operate rapidly.By this analysis, different cognitive control mechanisms underlie Stroop performance. One control mechanism appears to operate slowly and strategically at a list level, acting prior to stimulus onset. A second appears to operate rapidly at a trial or item-specific level, and acts after the stimulus has been presented. This...

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