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Psychon Bull Rev. 2014 Aug;21(4):1080-6. doi: 10.3758/s13423-013-0579-9.

More complex brains are not always better: rats outperform humans in implicit category-based generalization by implementing a similarity-based strategy.

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Laboratory of Biological Psychology, University of Leuven (KU Leuven), Tiensestraat 102, B3000, Leuven, Belgium,


Generalization from previous experiences to new situations is a hallmark of intelligent behavior and a prerequisite for category learning. It has been proposed that category learning in humans relies on multiple brain systems that compete with each other, including an explicit, rule-based system and an implicit system. Given that humans are biased to follow rule-based strategies, a counterintuitive prediction of this model is that other animals, in which this rule-based system is less developed, might generalize better to new stimuli in implicit category-learning tasks that are not rule-based. To test this prediction, rats and humans were trained in rule-based and information-integration category-learning tasks with visual stimuli. The generalization performance of rats and humans was equal in rule-based categorization, but rats outperformed humans on generalization in the information-integration task. The performance of rats was consistent with a nondimensional, similarity-based categorization strategy. These findings illustrate through a comparative approach that the bias toward rule-based strategies can impede humans' performance on generalization tasks.

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