When learning rule-based categories, sufficient cognitive resources are needed to test hypotheses, maintain the currently active rule in working memory, update rules after feedback, and to select a new rule if necessary. Prior research has demonstrated that conjunctive rules are more complex than unidimensional rules and place greater demands on executive functions like working memory. In our study, event-related potentials (ERPs) were recorded while participants performed a conjunctive rule-based category learning task with trial-by-trial feedback. In line with prior research, correct categorization responses resulted in a larger stimulus-locked late positive complex compared to incorrect responses, possibly indexing the updating of rule information in memory. Incorrect trials elicited a pronounced feedback-locked P300 elicited which suggested a disconnect between perception, and the rule-based strategy. We also examined the differential processing of stimuli that were able to be correctly classified by the suboptimal single-dimensional rule ("easy" stimuli) versus those that could only be correctly classified by the optimal, conjunctive rule ("difficult" stimuli). Among strong learners, a larger, late positive slow wave emerged for difficult compared to easy stimuli, suggesting differential processing of category items even though strong learners performed well on the conjunctive category set. Overall, the findings suggest that ERP combined with computational modelling can be used to better understand the cognitive processes involved in rule-based category learning.

The facilitatory effect shown in native speakers processing idiomatic phrases compared to matched novel phrases may be explained by a dual route model. This postulates that all phrases are processed literally at first, and if a phrase was recognized as familiar during processing, it would then be processed by a faster retrieval-route; if the phrase was not perceived as familiar, it would continue to be processed literally by the slower computation-route. The goals of the current project were to test the dual route model and to decipher the underlying mechanism in retrieval-route activation. English idioms and translated Chinese idioms were presented to both native English speakers and Chinese-English bilinguals in a random order. Participants listened to the idiom up until the last word (e.g., "draw a snake and add"), then saw either the idiom ending (e.g., "feet") or the matched control ending (e.g., "hair"); to which they made lexical decision and reaction times were recorded. We examined the priming effect for idioms compared to controls across the two language groups. The results showed that the two groups processed idioms of different origins differently. Native English speakers' faster responses to English idioms than controls supported a dual route model; however, both native English and bilingual speakers' faster responses to Chinese idioms than controls called for a less straightforward interpretation. Public Significance StatementThis study advances the idea that people process familiar idioms from their native language with more ease compared to matched non-idiomatic phrases. The bilingual participants in this study showed that an idiom-processing advantage may also occur when familiar idioms are processed in their translation equivalent forms in another language. These results imply that the knowledge embedded in native language plays a significant role in second language comprehension.

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Transient affective states have been shown to affect cognition, including category learning, but less is known about the role of stable temperament traits and categorization. We examined affective temperament traits to see whether the tendency to experience negative and positive affect is predictive of category learning performance and strategy use. Working memory and attentional control were measured as covariates. Participants first completed the Adult Temperament Questionnaire (Evans & Rothbart, 2007) including two affective temperament factors and an attentional control factor. Then they completed a memory task followed by either a conjunctive rule-based (CR) or an information integration (II) category learning task. Results showed that people who tend to experience more positive affect and less negative affect achieved higher accuracy and were more likely to find the optimal strategy in the II task compared to people who tend to experience more negative affect and less positive affect. However, no performance or strategy use difference was seen in the CR task across different temperament profiles. These results extend prior literature and provide additional insights on the effects of stable traits on category learning.