Infants and toddlers discriminate amount: are they measuring?

Four experiments that show an early ability to encode and retain information about extent are presented. We found that infants discriminate between the heights of dowels in a habituation task. We also found that toddlers discriminate between heights on a choice task in which a target dowel is presented and removed and they then choose between the target and a foil. Until 4 years of age, however, discrimination occurs only in the presence of a perceptually salient standard. Adults do not require a perceptually present standard; they can assess extent across temporal or spatial gaps by imposing a standard (measure). The present findings indicate that infants and toddlers do not possess an adult ability to establish extent, but that they do possess a skill that provides a start point for this important intellectual achievement.