In order to study the relationship between neonatal exercise and motor development, a professor randomly assigns 50 one-week-old infants to Group A or Group B. The 25 infants in Group A participate in a daily 15-minute exercise program. Infants in Group B are not exposed to anything beyond their normal daily activities. Twice a month for an entire year, subjects from both groups are given a motor skills test. What is the independent variable and dependent variable?