Numerosity discrimination in infants: evidence for two systems of representations.

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.