The evaluative role of rostrolateral prefrontal cortex in rule-based category learning

Abstract

Category learning is a critical neurobiological function that allows organisms to simplify a complex world. Rostrolateral prefrontal cortex (rlPFC) is often active in neurobiological studies of category learning; however, the specific role this region serves in category learning remains uncertain. Previous category learning studies have hypothesized that the rlPFC is involved in switching between rules, whereas others have emphasized rule abstraction and evaluation. We aimed to clarify the role of rlPFC in category learning and dissociate switching and evaluation accounts using two common types of category learning tasks: matching and classification. The matching task involved matching a reference stimulus to one of four target stimuli. In the classification task, participants were shown a single stimulus and learned to classify it into one of two categories. Matching and classification are similar but place different demands on switching and evaluation. In matching, a rule can be known with certainty after a single correct answer. In classification, participants may need to evaluate evidence for a rule even after an initial correct response. This critical difference allows isolation of evaluative functions from switching functions. If the rlPFC is primarily involved in switching between representations, it should cease to be active once participants settle on a given rule in both tasks. If the rlPFC is involved in rule evaluation, its activation should persist in the classification task, but not matching. The results revealed that rlPFC activation persisted into correct trials in classification, but not matching, suggesting that it continues to be involved in the evaluations of evidence for a rule even after participants have arrived at the correct rule.

Model-based fMRI reveals co-existing specific and generalized concept representations

“…Both prototype and exemplar correlates showed numerical increases across learning in brain and behavior, suggesting strengthening of both types of representations in parallel. Prior work has suggested that there may be representational shifts during category-learning, but rather than shifting between exemplar and prototype representations, early learning may be focused on detecting simple rules and testing multiple hypotheses (Johansen & Palmeri, 2002;Nosofsky, Palmeri, & McKinley, 1994;Paniukov & Davis, 2018), whereas similarity-based representations such as prototype and exemplar representations may develop later in learning (Johansen & Palmeri, 2002). Our findings are consistent with this framework, with strong prototype and exemplar representations emerging across distinct regions primarily in the second half of learning.…”

Brain Mechanisms of Concept Learning

“…Specifically, people will tend to engage rules when confronted with a stimulus that is both novel and difficult to categorize given the previously learned category representations. In support of this hypothesis, using an iterative rule-learning task, Paniukov and Davis (2018) found that the rlPFC is engaged early in learning and remains engaged as long as uncertainty remains about the correct category rule. Davis et al (2017) showed that the rlPFC was more engaged during acquisition of relational category-learning rules than acquisition of feature-based category rules.…”

“…Within the prefrontal cortex, ventromedial prefrontal cortex has been of interest in categorization because of its involvement in other forms of generalization, such as representation of schemas (van Kesteren et al, 2012;Gilboa and Marlatte, 2017) and linking related memories into an integrated representation . Hierarchical control theory, suggesting a possible rostrocaudal gradient of representational abstraction across the lateral prefrontal cortex (Badre and D'esposito, 2009;Badre and Nee, 2018), has inspired recent work on characterizing how distinct category learning contexts differentially engage specific cognitive control mechanisms and reasoning processes supported by subregions of lateral PFC (Paniukov and Davis, 2018). Finally, computational neuroimaging approaches have identified processes and representations contributed by the lateral parietal cortex, a region that has not played a major role in systems-level dissociations, but importantly contains both stimulus-specific and categorical memory representations Assad, 2006, 2016;Kuhl and Chun, 2014;Sestieri et al, 2017).…”

Model-based fMRI reveals dissimilarity processes underlying base rate neglect

“…For example, relational reasoning tasks such as Raven’s progressive matrices and rule-based tasks involving abstract relations are thought to depend on left rlPFC ( Christoff et al, 2001 ; Bunge et al, 2005 , Bunge et al, 2009 ; Davis et al, 2017 ). In addition to its role in generalizing abstract, relational rules, we have recently found left rlPFC to be involved in rule evaluation and novel generalization processes for simpler feature-based rules in categorization tasks ( Paniukov and Davis, 2018 ). In the present study, dissimilarity-based generalization to novel feature pairings may depend on rule evaluation processes in the rlPFC more so than simple similarity-based processing, if studies anticipating that dissimilarity-based processes depend more upon higher-level symbolic rules are correct ( Juslin et al, 2001 ; Winman et al, 2005 ).…”