Brief article Numerosity discrimination in infants: Evidence for two systems of representations Fei Xu * Department of Psychology-125NI, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, USA Received 11 November 2002; revised 19 February 2003; accepted 7 March 2003 Abstract Two experiments investigated numerosity discrimination in 6-month-old infants, comparing their performance on both large numbers (4 vs. 8 elements) and small numbers (2 vs. 4 elements) with both total filled area and total contour length controlled for. These studies provide the first direct comparison between discrimination of small and large numbers in infants with the same methodology, the same type of stimuli, and the same continuous variable controls. Results showed that infants succeeded in discriminating 4 from 8 elements but failed to discriminate 2 from 4 elements, providing evidence for the existence of two systems of number representations in infancy. q 2003 Elsevier Science B.V. All rights reserved. Keywords: Numerosity discrimination; Infants 1. Introduction The last few decades have witnessed a wealth of studies on number representations in infants, adults, and non-human animals (see Dehaene, 1997; Gallistel, 1990; Gallistel & Gelman, 2000; Wynn, 1998, for reviews). In recent years the debate on whether infants represent numerosity per se has inspired many new empirical investigations (e.g. Simons, Hespos, & Rochat, 1995; Uller, Carey, Huntley-Fenner, & Klatt, 1999; Wynn, 1992). Early studies reported that infants can discriminate between small numbers of 2D visual forms or objects (e.g. Antell & Keating, 1983; Starkey & Cooper, 1980; Starkey, Spelke, & Gelman, 1983; Strauss & Curtis, 1981; Treiber & Wilcox, 1984). However, because these studies confounded number with other continuous variables (e.g. larger number 0022-2860/03/$ - see front matter q 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0010-0277(03)00050-7 Cognition 89 (2003) B15–B25 www.elsevier.com/locate/COGNIT * Tel.: þ1-617-373-3060; fax: þ 1-617-373-8714. E-mail address: f.xu@neu.edu (F. Xu).