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The Difficulties of Representing Continuous Extent in Infancy: Using Number Is Just Easier


  • We thank Donna Lutz, Sumarga Suanda, Klaus Libertus, Melissa Libertus, and a team of undergraduate research assistants for help in data collection. We also thank the parents and infants who participated in the research as well as the members of the Brannon Lab for their thoughtful comments on the manuscript. The research reported here was supported by an RO1 MH066154 award, a National Science Foundation CAREER award, and a Merck Scholars award to E.M.B. and a postdoctoral fellowship to S.C.

concerning this article should be addressed to Sara Cordes, Center for Cognitive Neuroscience, Duke University, Box 90999, Durham, NC 27708. Electronic mail may be sent to


This study investigates the ability of 6-month-old infants to attend to the continuous properties of a set of discrete entities. Infants were habituated to dot arrays that were constant in cumulative surface area yet varied in number for small (< 4) or large (> 3) sets. Results revealed that infants detected a 4-fold (but not 3-fold) change in area, regardless of set size. These results are in marked contrast to demonstrations that infants of the same age successfully discriminate a 2- or 3-fold change in number, providing strong counterevidence to the claim that infants use solely nonnumerical, continuous extent variables when discriminating sets. These findings also shed light on the processes involved in tracking continuous variables in infants.

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