Arnold GesellBorn 21 Jun 1880; died 29 May 1961 at age 80.Arnold Lucius Gesell was an American psychologist and pediatrician who pioneered the use of motion-picture cameras (1926) to study the physical and mental development of normal infants and children. His books gave norms for behavior at successive stages of development and were widely read by parents. Gesell was one of the first to attempt a quantitative study of child development, developing his own methods of observation and measurement. Gesell's initial work focused on developmentally disabled children, but he believed that it was necessary to understand normal infant and child development in order to understand nonnormality. He also studied Down's syndrome, cretinism, and cerebral palsy.