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We present four experiments with the object-examining procedure that investigated 7-, 9-, and 11-month-olds' ability to associate two object features that were never presented simultaneously. In each experiment, infants were familiarized with a number of 3D objects that incorporated different correlations among the features of those objects and the body of the objects (e.g., Part A and Body 1, and Part B and Body 1). Infants were then tested with objects with a novel body that either possessed both of the parts that were independently correlated with one body during familiarization (e.g., Part A and B on Body 3) or that were attached to two different bodies during familiarization. The experiments demonstrate that infants as young as 7months of age are capable of this kind of second-order correlation learning. Furthermore, by at least 11months of age infants develop a representation for the object that incorporates both of the features they experienced during training. We suggest that the ability to learn second-order correlations represents a powerful but as yet largely unexplored process for generalization in the first years of life.

In this article, we review the principal findings on infant categorization from the last 30 years. The review focuses on behaviorally based experiments with visual preference, habituation, object examining, sequential touching, and inductive generalization procedures. We propose that although this research has helped to elucidate the 'what' and 'when' of infant categorization, it has failed to clarify the mechanisms that underpin this behavior and the development of concepts. We outline a number of reasons for why the field has failed in this regard, most notably because of the context-specific nature of infant categorization and a lack of ground rules in interpreting data. We conclude by suggesting that one remedy for this issue is for infant categorization researchers to adopt more of an interdisciplinary approach by incorporating imaging and computational methods into their current methodological arsenal. WIREs Cogn Sci 2010 1 894-905 For further resources related to this article, please visit the WIREs website.

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Connectionist models have been applied to many phenomena in infant development including perseveration, language learning, categorization, and causal perception. In this article, we discuss the benefits of connectionist networks for the advancement of theories of early development. In particular, connectionist models contribute novel testable predictions, instantiate the theorized mechanism of change, and create a unifying framework for understanding infant learning and development. We relate these benefits to the 2 primary approaches used in connectionist models of infant development. The first approach employs changes in neural processing as the basis for developmental changes, and the second employs changes in infants' experiences. The review sheds light on the unique hurdles faced by each approach as well as the challenges and solutions related to both, particularly with respect to the identification of critical model components, parameter specification, availability of empirical data, and model comparison. Finally, we discuss the future of modeling work as it relates to the study of development. We propose that connectionist networks stand to make a powerful contribution to the generation and revision of theories of early child development. Furthermore, insights from connectionist models of early development can improve the understanding of developmental changes throughout the life span. Keywords: connectionist modeling, neural network modeling, parallel distributed processing, infant developmentSince the groundbreaking work of Rumelhart and McClelland in the 1980s, there has been an increasing interest in and research on the application of connectionist models to early human development. Connectionist models are instantiations of theories about the mechanisms that underpin particular behaviors. Building computational models allows for the exploration of the interaction of numerous factors both internal and external to the organism that typically contribute to a behavior, which often can be too complex to specify through verbal theory alone . These computational models provide researchers with a number of ways to explicitly test theoretical assumptions and develop novel and testable predictions.However, in our view, for many developmental scientists the contribution of models to an integrated understanding of development is far from clear. Although a given model might provide output that is similar to the behavior of infants, it often remains to be seen whether the model's results and the behavioral results occur for the same reasons. For example, a network may simulate effectively infants' ability to discriminate between two objects that differ along multiple features, but it is possible that the features used by the network for discrimination are different from those used by infants. Computational models have also been criticized for using overly technical terms and notations that may be offputting to nonexperts (Klahr, 2004); for not being explicit about the source of their starting states (Oakes, Newcom...

We evaluate the heterogeneity hypothesis by considering the developmental time course and the mechanism of acquisition of exemplars, prototypes, and theories. We argue that behavioral and modeling data point to a sequential emergence of these three types of concepts within a single system. This suggests that similar or identical underlying cognitive processes -rather than separate ones -underpin representation acquisition. Doing without Conceptsproposes an interesting solution to the problem of applying the term "concept" to prototypes, exemplars, and theories, which according to the Machery, are unrelated. Each type of concept engages a distinct cognitive process -such as similarity comparison or causal inference -so that a unified label is inappropriate. The book synthesizes an impressive amount of literature in psychology and philosophy to provide evidence for this heterogeneity hypothesis. From the point of view of developmental psychology, however, two key questions remain unanswered. First, what is the time course for the emergence of prototypes, exemplars, and theories? Second, and more importantly, what is the mechanism behind their formation? Specifically, does each require a dedicated mechanism, or is a single system sufficient? In our view, an answer to the second question is particularly important for our ability to evaluate the proposal that distinct cognitive processes underlie the use of prototypes, exemplars, and theories.Answering the first question is an important component to answering the second question. If exemplars, prototypes, and theories emerge in succession and not simultaneously, then it is possible that they build upon each other. This could suggest the development of a single mechanism or, at the very least, the development of three related mechanisms. While no single study provides definitive evidence, a pattern of successive emergence can be observed across studies. As an example, we can examine infants' knowledge about individuals. Threemonth-old infants can discriminate an image of their mother's face from that of a stranger (Barrera & Maurer 1981), which suggests that they have stored an exemplar of their mother's appearance. By 6 months of age, infants can extract a prototype from a series of faces and display a preference for a novel face when it is presented with either a familiar face or the previously unseen prototype (Rubenstein et al. 1999). By 10 months, infants display more theory-like knowledge about individuals in that they do not generalize goaldirected actions, such as reaching for an object, from one individual to another (Buresh & Woodward 2007). This task requires not only theoretical knowledge about the properties of goals but also the ability to store exemplars of the individuals so that goals may be matched correctly. Taken together, these studies provide some support for the sequential emergence of exemplars, prototypes, and theories.In addition to determining the time course for these processes, the most important developmental question with respect...