The Proceedings of the National Academy of Sciences (2009) describes the research conducted by Agnes Melinda Kovacs and Jacques Mehler on the cognitive gains in seven-month-old bilingual infants. In three eye-tracking studies, Kovacs and Mehler found that infants, reared with two languages from birth, display improved cognitive control abilities compared with matched monolinguals.
^Mehler, J.; Jusczyk, P.; Lambertz, G.; Halsted, N.; Bertoncini, J.; Amiel-Tison, C. (1988). "A precursor of language acquisition in young infants". Cognition29 (2): 143. doi:10.1016/0010-0277(88)90035-2.