Infant number perception : a developmental approach

Infant number perception is a topic that has been studied for many years, but many questions remain regarding what cues infants use to make these discriminations, when and how these abilities develop, and what systems are responsible for infants’ number processing. In the domain of small number perception (quantities less than four), researchers have studied the effects of continuous extent on infants’ number discrimination (Clearfield & Mix, 1999; 2001). While evidence exists that infants can use continuous extent to make discriminations, it is not clear how much influence continuous extent has on infants’ behavior in these tasks. Another issue that has not been thoroughly addressed is the role of featural information in number discrimination. Few studies exist in which featural information is manipulated so that this issue can be addressed. The current study was designed to address these issues as well as to study infant number discrimination from a developmental perspective across several ages. Infants, aged 9-, 11-, and 13-months, completed a categorization task in which they were habituated to pictures of objects (e.g. bowl, tree, shoe) in either groups of two or groups of three. They saw four different sets of objects throughout habituation. In the test phase, infants saw both new and old objects in both groups of two and three. The 9-month-olds discriminated number independent of whether the object was familiar or novel. In contrast, the 11- month-olds appeared to discriminate between the familiar and novel objects. And, the 13-month-olds exhibited a combination of these two patterns; they discriminated between the familiar and novel object when the number of objects was familiar, but not when the number of objects was novel. These data suggest that number is an easily abstracted construct and that early number representations do not contain any featural information. As infants get older, they begin to incorporate featural information into their representations, but they do so in a step-wise fashion, as demonstrated by the 13-month-olds. Therefore, featural information does not appear to be important for small number discrimination at early ages, but infants do begin to integrate featural information as they develop.