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In the standard Proportion-Congruent (PC) paradigm, performance is compared between a list containing mostly congruent (MC) stimuli (e.g., the word RED in the color red in the Stroop task; Stroop, 1935) and a list containing mostly incongruent (MI) stimuli (e.g., the word BLUE in red). The PC effect, the finding that the congruency effect (i.e., the latency difference between incongruent and congruent stimuli) is typically larger in an MC list, has been interpreted by the popular conflict-monitoring account (Botvinick et al., 2001) as reflecting a proactive process whereby attention to task-relevant information is adapted based on how frequently conflict from task-irrelevant information arises. Recently, however, alternative accounts of the PC effect have emerged that assume either that the PC effect reflects processes other than proactive conflict adaptation (e.g., stimulus-response contingency learning) or that proactive conflict adaptation is only engaged as a last resort (e.g., when contingency learning cannot be used to minimize interference). We examined these ideas in three experiments in which proactive conflict adaptation could be evaluated independently from processes that are normally confounded with it in the PC paradigm, while still allowing those processes, particularly contingency learning, to be used to minimize interference. Consistent with the conflict-monitoring account of the PC effect, but inconsistent with all the alternative accounts of the PC effect, evidence for proactive conflict adaptation emerged in all experiments. Although multiple processes may be engaged in the PC paradigm, this paradigm remains a valid tool for examining proactive conflict adaptation, its typical use.

According to some accounts, the bilingual advantage is most pronounced in the domain of executive attention rather than inhibition and should therefore be more easily detected in conflict adaptation paradigms than in simple interference paradigms. We tested this idea using two conflict adaptation paradigms, one that elicits a list-wide proportion-congruent effect and one that elicits an item-specific proportion-congruent effect. In both cases, the relevant finding is that congruency effects are reduced when the proportion of congruent to incongruent items is smaller. These effects are validated measures of proactive and reactive control, respectively, and are aspects of executive attention known to be associated with individual differences in working memory capacity. We reasoned that if bilingualism affects executive attention in a similar way as does working memory capacity, indices of proactive and reactive control should be comparably associated with continuous variation in language status and working memory capacity. In two experiments, we replicated previous findings that working memory capacity is associated with variation in congruency effects (suggesting greater reliance on proactive control). In contrast, language status had no consistent association with performance, save for a hint that bilingualism may be associated with greater reliance on reactive control. Thus, the bilingual advantage may exist, but not in proactive control or any other aspects of executive attention that have been proposed thus far.

In the Stroop task, congruency effects (i.e., the color-naming latency difference between incongruent stimuli, e.g., the word BLUE written in the color red, and congruent stimuli, e.g., RED in red) are smaller in a list in which incongruent trials are frequent than in a list in which incongruent trials are infrequent. The traditional explanation for this pattern is that a conflict-monitoring mechanism adjusts attention to task-relevant versus task-irrelevant information in a proactive fashion based on list-wide conflict frequency. More recently, however, multiple alternative explanations have been advanced that could explain the pattern without invoking this form of proactive control: Individuals might only adapt to conflict frequency specific to individual items (as opposed to list-wide conflict frequency), they could learn word-color contingencies (e.g., how often a particular word and color are paired), or they could adapt attention based on whether the words are informative of the color (even if many word-color pairings are incongruent) in the list as a whole. To examine this issue, we designed a new paradigm that should eliminate any impact of these alternative mechanisms. In that paradigm, the proportion of neutral (e.g., XXX in red) and incongruent stimuli was manipulated across lists. Paralleling the results in the original paradigm, there was a smaller latency difference between incongruent and neutral stimuli in a list in which incongruent trials were frequent than in a list in which incongruent trials were infrequent, suggesting that proactive control in response to list-wide conflict frequency is a process humans can and do use.

A word's exterior letters, particularly its initial letter, appear to have a special status when reading. Therefore, most orthographic coding models incorporate assumptions giving initial letters and, in some cases, final letters, enhanced importance during the orthographic coding process. In the present article, 3 masked priming experiments were carried out, using the conventional lexical-decision task, the sandwich priming lexical-decision task and the masked priming same-different task, in an attempt to examine a number of those models with a specific focus on the implications of the models' assumptions concerning the different letter positions. The related primes and targets were 6-letter strings that differed in 2 letter positions, initial (e.g., "jnckey-HOCKEY"), middle (e.g., "hojney-HOCKEY"), or final ("hockjn-HOCKEY"), with the middle-letters different primes being the primes that maintained both end letters. To the extent possible, the predictions of the models were derived by using easyNet, the simulation program recently developed by Adelman, Gubian, and Davis (2017). In all experiments, the final-letters different primes were the most effective primes with there being no clear distinction between the other 2 prime types, a pattern that none of the models predicted. The lack of an advantage for the middle-letters different primes suggests that the orthographic code driving masked priming is not one that places a special emphasis on the identities of the exterior letters.

A consistent finding in the Stroop literature is that congruency effects (i.e., the color-naming latency difference between words presented in incongruent vs. congruent colors) are larger for mostly-congruent items (e.g., the word RED presented most often in red) than for mostly-incongruent items (e.g., the word GREEN presented most often in yellow). This "item-specific proportion-congruent effect" might be produced by a conflict-adaptation process (e.g., fully focus attention to the color when the word GREEN appears) and/or by a more general learning mechanism of stimulus-response contingencies (e.g., respond "yellow" when the word GREEN appears). Under the assumption that limited-capacity resources are necessary for learning stimulus-response contingencies, we examined the contingency-learning account using both Stroop and nonconflict (i.e., noncolor words written in colors) versions of a color identification task while participants maintained a working memory (WM) load. Consistent with the contingency-learning account, WM load modulated people's ability to learn contingencies in the nonconflict task. In contrast, across 3 experiments, WM load did not affect the item-specific proportion-congruent effect in the Stroop task even though we employed a design (the "2-item set" design) in which contingency learning should be the dominant process. These results imply that the item-specific proportion-congruent effect is not merely a byproduct of contingency learning but a manifestation of reactive control, a mode of control engagement that may be especially useful when WM resources are scarce.

Does visuospatial orientation influence repetition and transposed character (TC) priming effects in logographic scripts? According to perceptual learning accounts, the nature of orthographic (form) priming effects should be influenced by text orientation (Dehaene, Cohen, Sigman, & Vinckier, 2005; Grainger & Holcomb, 2009). In contrast, Witzel, Qiao, and Forster's (2011) abstract letter unit account argues that the mechanism responsible for such effects acts at a totally abstract orthographic level (i.e., the visuospatial orientation is irrelevant to the nature of the relevant orthographic code). The present experiments expanded this debate beyond alphabetic scripts and the syllabic Kana script used by Witzel et al. to a logographic script (Chinese). Experiment 1 showed masked repetition and TC priming effects with primes and targets presented in both the conventional left-to-right horizontal orientation and the vertical top-to-bottom orientation, replicating Witzel et al. Experiment 2 showed masked repetition and TC priming effects even when both the primes and targets were presented in the right-to-left orientation, a rare but existent text orientation in Chinese. In Experiment 3, the primes, but not the targets, were presented in the right-to-left orientation. Priming effects were again obtained regardless of the fact that the primes and targets appeared in different orientations. Experiment 4, which involved primes and targets presented in a completely novel bottom-to-top orientation, also produced a TC priming effect. These results support abstract letter/character unit accounts of form priming effects while failing to support perceptual learning accounts.