The ability to process information with minimum, or even no effort, is known as automaticity. This can be observed in very young children when they concentrate on one topic while performing a routine task. Adolescents can be observed demonstrating automaticity when asked to answer a list of very basic arithmetic. The concept here is that a task has been so coded in the brain of the individual that concentration efforts may be diverted and the task performed with near automation.
The effect over time that learning plays in automaticity is obvious. Any task that has reached a level of automaticity requires more concentration for people of equivalent potential of lesser age and experience. As automaticity increases a person's speed and processing capabilities also increase. As processing ability increases, automaticity increases, the task difficulty decreases, and multitasking capabilities start surfacing.
Resources include: Siegler, R.S. (1991). Children’s thinking (2nd ed.). Englewood Cliffs, NJ: Prentice Hall.