Active involvement in purposeful activity is necessary for capacities to become functional and to allow continuous adaptation. The adequacy of a person's functional capacities is influenced by the demands and expectations of the internal and external environments and by the internal resources available to support and promote development. Successful experience in problem sensing, posing, and resolution facilitates a person's ability to function adequately. An individual's internal environment is influenced by its own internal tendencies and the demands placed upon it. Function is influenced by physical structure and by the ability to receive sensory stimuli, organize them into meaningful units and initiate a response.
People have the capacity for thought and sensation.
They are capable of abstraction, imagery and language, and capable of feelings and emotions. A person's external environment consists of people, objects, and events. This environment includes the physical, cultural, economic and social settings in which the person operates. People are constantly influencing and being influenced by their external environment. They can accept, reject, and modify their environments and have the potential to create, destroy, or modify linkages between themselves and the environment.