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Single and multiple systems in probabilistic categorization

Nature Reviews Psychology volume 4, page 64 (2025)Cite this article

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The ongoing debate about whether people use multiple memory systems (separate modules for rule-based and implicit learning) or a single explicit rule-based system for categorization remains unresolved. In their Review, Minda and colleagues (Minda, J. P., Roark, C. L., Kalra, P. & Cruz, A. Single and multiple systems in categorization and category learning. Nat. Rev. Psychol. 3, 536–551 (2024))1 discussed the past 30 years of categorization research and concluded that a specific multiple-system account — the competition between verbal and implicit systems (COVIS) model — is the best available account of most categorization phenomena. However, the Review does not consider evidence related to probabilistic categorization, an experimental paradigm in which perfect performance is unattainable. Consequently, the authors also do not address how the COVIS model would handle probabilistic categorization. We suggest that probabilistic categorization presents methodological and empirical challenges to the multiple-system accounts and furthers the debate in the field.

The probabilistic categorization paradigm was designed to distinguish between multiple and single accounts of category learning by biasing people towards an associative strategy at least during early stages of learning2. For instance, individuals with damage to the medial temporal lobes and an intact corticostriatal system performed as well as unimpaired adults during the first 50 trials of a task in which combinations of cards are probabilistically associated with 2 possible outcomes2. By contrast, individuals with degeneration of the corticostriatal system and intact medial temporal lobes performed, overall, worse than unimpaired adults, even across different training days3. Both of these findings suggest that during the first 50 trials of the task, neither unimpaired adults nor individuals with brain damage used an explicit rule2. This pattern has led researchers to believe that the initial learning phases of probabilistic categorization paradigms rely on procedural habit learning rather than explicit rules, involving basal ganglia corticostriatal dopaminergic projections, with minimal involvement of the medial temporal lobe4.

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  1. Center of Cognitive and Social Neuroscience, School of Psychology, Universidad Adolfo Ibáñez, Santiago, Chile

    Nicolás Marchant & Sergio E. Chaigneau

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  1. Nicolás Marchant
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  2. Sergio E. Chaigneau
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Correspondence to Nicolás Marchant.

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Marchant, N., Chaigneau, S.E. Single and multiple systems in probabilistic categorization. Nat Rev Psychol 4, 64 (2025). https://doi.org/10.1038/s44159-024-00389-8

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