Tracking and quantifying objects and non-cohesive substances.

The present study tested infants' ability to assess and compare quantities of a food substance. Contrary to previous findings, the results suggest that by 10 months of age infants can quantify non-cohesive substances, and that this ability is different in important ways from their ability to quantify discrete objects: (1) In contrast to even much younger infants' ability to discriminate discrete quantities that differ by a 1:2 ratio, infants here required a 1:4 ratio in order to reliably select the larger of two substance quantities. And (2), unlike with objects, infants required multiple cues in order to determine which of two quantities of substance was larger. Moreover, (3) although 14.5-month-olds were able to compare amounts of substance in memory, 10- to 12-month-olds were limited to comparing visible amounts of substance. These findings are discussed in light of the mechanisms that may underlie infants' quantification of objects and substances.