Perceptual Category Learning: Similarity and Differences Between Children and Adults

Perceptual Category Learning: Similarity and Differences Between Children and Adults Rahel Rabi (rrabi@uwo.ca) Department of Psychology, The University of Western Ontario London, ON N6A 5C2 CANADA John Paul Minda (jpminda@uwo.ca) Department of Psychology, The University of Western Ontario London, ON N6A 5C2 CANADA Abstract Studies of category learning have supported the idea that peo- ple rely on at least two cognitive systems when learning new categories. A verbally-mediated system is best suited for learning rule-based categories, and a nonverbal, procedural system is best suited for learning categories that are not de- fined by a rule. To further examine the cognitive systems in- volved in categorization, two experiments explored develop- mental differences in perceptual category learning. In the first experiment, children and adults were asked to learn a set of categories consisting of stimuli equated on feature salience. A single-feature rule (the criterial attribute) or overall similarity would allow for perfect performance on this task. We found that adults made significantly more rule-based responses to the test stimuli than did children. A second experiment exam- ined non-rule-based category learning by having children and adults complete a prototype abstraction task. Children showed evidence of prototype abstraction, with many children show- ing a similar pattern of responding to adults. Results are dis- cussed within the COVIS framework. Keywords: Category learning; Development; COVIS Introduction Categorization is a fundamental process that allows us to meaningfully parse the world, and to group like objects to- gether so that they can be treated equivalently. This process has been examined in both adults and children (Ashby & Maddox, 2005; Minda, Desroches, & Church, 2008; Huang- Pollock, Maddox, & Karalunas, 2011; Rabi & Minda, 2014), with research suggesting that children have a reduced capacity for executive functioning and rule selection (Bunge & Zelazo, 2006; Casey et al., 2004). Due to these limited capacities, adults should outperform children on categoriza- tion tasks involving rule selection, but performance differ- ences should be minimized in cases where to be learned categories have little or no rule selection component. One way to understand any possible differences between children and adults is to consider the possibility that multi- ple cognition systems underlie category learning. According to multiple-systems theories (the Competition between Ver- bal and Implicit Systems, or COVIS, is a well known exam- ple) a verbal system is assumed to learn rule-based catego- ries (Ashby et al., 1998). This system is mediated primarily by the prefrontal cortex, the medial temporal cortex, the anterior cingulate cortex, and the head of the caudate. This system requires sufficient cognitive resources to search for, store, and apply a rule (Zeithamova & Maddox, 2006). This system is assumed to be the default approach for normally- functioning adults when learning new categories (Ashby et al., 1998). The multiple-systems approach also assumes that a nonverbal system learns non-rule-based categories. The nonverbal system is mediated by sub-cortical structures in the tail of the caudate nucleus, relies on a dopamine- mediated reward signal to learn, and does not rely as heavily on verbal working memory and controlled attention. This system is well suited to learn categories that have a strong family resemblance (FR) structure (Ashby et al., 1998). It is not well suited for rapid rule learning or for categories that require a disjunctive rule and thus have no clear family re- semblance structure (Minda et al., 2008). Both systems compete during learning and when a classification decision is made. Ultimately, the system with the more successful responding strategy will tend to dominate performance (Ashby et al., 1998). COVIS and other multiple-systems theories make several predictions about developmental effects on category learn- ing, because the regions of interest are known to develop with age. For example, research has shown that develop- mental changes in rule use reflect the rate of development of the prefrontal cortex (Bunge & Zelazo, 2006). As such, we might expect age-related improvements in explicit rule- based categorization if the prefrontal cortex is assumed to mediate many of the cognitive aspects of the verbal system (hypothesis testing, selective attention, etc.). In contrast, the nonverbal system is mediated by the tail of the caudate nu- cleus, which seems to be fully developed in children (Casey et al., 2004). Thus, young children should be able to learn non-rule-based categories in a similar manner to adults. Prior research has consistently demonstrated age-related improvements in rule-based category learning. For example, Minda, Desroches, and Church (2008) compared categoriza- tion performance in 3-, 5-, and 8-year-olds, as well as adults. Results revealed that adults outperformed children on categories that were optimally learned by a disjunctive rule (e.g., 2 of the 3 stimulus features were relevant for the disjunctive rule). However, children could learn single- dimensional rules about as well as adults, suggesting that the ability to learn rules was not completely absent in chil- dren. Huang-Pollock and colleagues (2011) examined the ability of school-aged children and adults to learn rule-based or non-rule-based categories. They found that the adults performed better than the children in both cases, and the