The Difficulties of Representing Continuous Extent in Infancy: Using Number Is Just Easier

Abstract

This study investigates the ability of 6-month-old infants to attend to the continuous properties of a set of discrete entities. Infants were habituated to dot arrays that were constant in cumulative surface area yet varied in number for small (< 4) or large (> 3) sets. Results revealed that infants detected a 4-fold (but not 3-fold) change in area, regardless of set size. These results are in marked contrast to demonstrations that infants of the same age successfully discriminate a 2- or 3-fold change in number, providing strong counterevidence to the claim that infants use solely nonnumerical, continuous extent variables when discriminating sets. These findings also shed light on the processes involved in tracking continuous variables in infants.

Numerosity representation is encoded in human subcortex

“…As development proceeds, however, the system becomes more finely tuned to smaller differences in quantities. Consistent with this, infants as young as 48 h are able to differentiate ratios of 3:1 but not 2:1 (20), and, as they age, children show increasingly precise abilities: at 6 mo, they can distinguish ratios of 2:1, and by 9 mo, ratios of 3:2 (21,22). They eventually reach competencies for ratios 4:3 by 3 y, 6:5 by 6 y, and 8:7 and more difficult ratios by adulthood (23)(24)(25)(26).…”

“…Specifically, we expect the subcortical mechanism to respond selectively to nonsymbolic quantities (here, dot arrays) given that symbolic manipulation of quantities is uniquely human and likely requires cortical contributions. Moreover, we predict that subcortical contributions to number processing will be ratio dependent as young children evince numerical abilities that are themselves ratio dependent (20)(21)(22).…”

Visual nesting impacts approximate number system estimation

“…ANS estimations can be influenced by perceptual factors, such as regularity of spacing (Ginsburg, 1976(Ginsburg, , 1978Taves, 1941), perceived area (van Oeffelen & Vos, 1982Vos, van Oeffelen, Tibosch, & Allik, 1988), and item segmentation (Franconeri et al, 2009). While some claim that ANS estimations are based solely on continuous extent features, such as area and density (Mix, Huttenlocher, & Levine, 2002), other research indicates that the ANS can assess numerosity even when continuous extent is controlled (Cordes & Brannon, 2008;Hurewitz, Gelman, & Schnitzer, 2006). Meck and Church's (1983) accumulator model proposes that numerosities are assessed by tallying items, rather than derived from continuous extent.…”

Rapid and Direct Encoding of Numerosity in the Visual Stream

“…However, very little is known about how luminance perception is carried out at the behavioral and the neural level when a set of items rather than a single item is presented, especially when the array size is well beyond the subitizing range. Behavioral studies in infants demonstrate that while infants are quite sensitive to changes in the size of a single item, when presented with sets of items infants are much more sensitive to changes in numerosity than to total item area (Cordes and Brannon 2008) or to individual item area (Cordes and Brannon 2011). These previous behavioral findings, along with our results, suggest that the prevailing assumption that some continuous variables are always more salient than number in dot arrays may require a serious reconsideration.…”