Although there has to be a stark difference in the choices for infants to recognize the correct matching set of numbers (1:3 vs 1:2), this seems to prove that infants have an innate numerical sense, but it may not be the same numerical sense as older children. Around the age of three and a half years children lose some of their numerical sense. Whereas children younger than three can recognize that four pebbles spread out in a line is less than six pebbles scrunched together in a line, children around the age of three and a half mysteriously lose this ability. Researchers believe that this is because children around this age begin to rely heavily on the physical properties of the world and objects within it, such that longer equals more. Although the ability to recognize that six pebbles closely lined up together is more than four pebbles spread out farther from one another goes away around that age, it comes back around four years of age when children begin to count.