In psychological theory, learning behavior is controlled by environmental influences rather than by innate or internal forces. The leading exponent of the concept of social learning (often called modeling) is the American psychologist Albert Bandura, who has undertaken innumerable studies showing that when children watch others they learn many forms of behavior, such as sharing, aggression, cooperation, social interaction, and delay of gratification. Social concept of social learning evolved from an awareness that much learning takes place as a result of learning and imitating other people's behavior (Bandura & Walters, 1963). Changes in behavior can be linked to a specific pattern of positive or negative reinforcement. They can also occur with numerous opportunities of trial-and-error practice. A person can watch someone perform a task or say a new expression and imitate hat behavior accurately on the first try.