Abstract
A prominent theory of category learning, COVIS, posits that new categories are learned with either a declarative or procedural system, depending on the task. The declarative system uses the prefrontal cortex (PFC) to learn rule-based (RB) category tasks in which there is one relevant sensory dimension that can be used to establish a rule for solving the task, whereas the procedural system uses corticostriatal circuits for information integration (II) tasks in which there are multiple relevant dimensions, precluding use of explicit rules. Previous studies have found faster learning of RB versus II tasks in humans and monkeys but not in pigeons. The absence of a learning rate difference in pigeons has been attributed to their lacking a PFC. A major gap in this comparative analysis, however, is the lack of data from a nonprimate mammalian species, such as rats, that have a PFC but a less differentiated PFC than primates. Here, we investigated RB and II category learning in rats. Similar to pigeons, RB and II tasks were learned at the same rate. After reaching a learning criterion, wider distributions of stimuli were presented to examine generalization. A second experiment found equivalent RB and II learning with wider category distributions. Computational modeling revealed that rats extract and selectively attend to category-relevant information but do not consistently use rules to solve the RB task. These findings suggest rats are on a continuum of PFC function between birds and primates, with selective attention but limited ability to utilize rules relative to primates.
Highlights
IntroductionA model of human category learning, COVIS (competition between verbal and implicit systems), posits that new categories are learned by two functionally and anatomically distinct neural systems: a declarative system and a procedural system (Ashby et al 1998; Ashby and Maddox 2005, 2010)
A model of human category learning, COVIS, posits that new categories are learned by two functionally and anatomically distinct neural systems: a declarative system and a procedural system (Ashby et al 1998; Ashby and Maddox 2005, 2010)
Results than the II tasks? On the one hand, one might predict that rats Experiment 1 would show a learning advantage for the RB tasks, as classic behavioral paradigms have demonstrated that rat cognition supports the Training executive functions described by COVIS’s declarative system, in- In the current experiment, rats were trained to learn either an RB or cluding working memory and selective attention
Summary
A model of human category learning, COVIS (competition between verbal and implicit systems), posits that new categories are learned by two functionally and anatomically distinct neural systems: a declarative system and a procedural system (Ashby et al 1998; Ashby and Maddox 2005, 2010). The declarative system uses executive functions (e.g., working memory and selective attention) to develop and utilize rules of the category task. Under this system, the learner explicitly tests hypotheses about potential rules, and feedback provides information regarding the validity of each rule. RB tasks entail category distributions that are perpendicular to one of the axes (in Fig. 1A, spatial frequency; in Fig. 1B, orientation), whereas the II tasks entail 45° rotations of the RB distributions (Fig. 1C,D) This rotation does not change any intrinsic property of the task (e.g., the RB and II tasks are identical in their logical separability and difficulty); the II tasks are no longer perpendicular to an axis. This species difference may importantly inform the evolutionary trajectory of category learning (Smith et al 2012), with primates able to represent RB tasks using rules, but avians forced to deploy a single associative learning system
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