ADDITION AND SUBTRACTION BY HUMAN INFANTS

HUMAN infants can discriminate between different small numbers of items1-4, and can determine numerical equivalence across perceptual modalities5,6. This may indicate the possession of true numerical concepts1,4-7. Alternatively, purely perceptual discriminations may underlie these abilities8,9. This debate addresses the nature of subitization, the ability to quantify small numbers of items without conscious counting10,11. Subitization may involve the holistic recognition of canonical perceptual patterns that do not reveal ordinal relationships between the numbers12, or may instead be an iterative or 'counting' process that specifies these numerical relationships4,13. Here I show that 5-month-old infants can calculate the results of simple arithmetical operations on small numbers of items. This indicates that infants possess true numerical concepts, and suggests that humans are innately endowed with arithmetical abilities. It also suggests that subitization is a process that encodes ordinal information, not a pattern-recognition process yielding non-numerical percepts.