Difficulty in learning new information because of already existing information. For example, an English speaking person may have greater difficulty learning Spanish because of his or her tendency to want to apply English grammar to the new language. Some people have a harder time learning how to drive an automatic vehicle because of their preexisting knowledge of how to drive a stick shift. The driver may want to use his or her left foot for the break where they are used to having the clutch. The same person may have learned to drive an automatic more easily without his or her knowledge of a standard car.
See also: Retroactive Interference