It has been known since 1992 that babies as young as five months can do simple arithmetic (1+1=2). However, it was not thought that young children could compare more fluid amounts of things, such as quantities of water or sand. Kristy VanMarie from the University of Missouri and Karen Wynn of Yale have found that babies as young as ten months old can tell a larger amount of cereal from a lesser amount.
The experiment was very simple. The researchers poured cereal into cups and let the babies choose which cup they preferred. Starting at about ten months, as long as one cup had at least three times as much as the other, the babies would consistently choose the larger amount. At around 14 months, the babies could even remember which cup held more when the amounts were poured into opaque cups.
As an aside, the arithmetic experiments (also run by Karen Wynn) relied on the babies’ attention spans, rather than on their ability to choose an object. As an example, the five-month old babies were shown one doll on a table. A screen was lowered in front of that doll. The babies then watched as an experimenter added one more doll behind the screen. When the curtain was raised, there were either one or two dolls there. If there was only one doll, the babies stared for a lot longer than if there were two dolls. In other words, the babies appeared to be nonchalant about the fact that 1+1=2 but surprised to find that 1+1=1. The same results were found with subtraction: babies stared longer when removing one doll from behind a screen did not appear to decrease the total number of dolls from 2 to 1.