 More often than not, individuals speaking two or more languages come into contact with one another, for reasons ranging from emigration and interrelationships to alterations in political borders.The result of such contact is typically that the community of speakers undergoes a progressive shift in usage from one language to the other.Gleason has also done significant research on aphasia,
a condition (usually due to brain injury) in which a person's ability to understand and/or to produce language, including their ability to find the words they need and their use of basic morphology and syntax, is impaired in a variety of ways.