Language disorders include primary and secondary language disorders. Primary speech disorders are defined as difficulty in pronunciation, slurred speech, lack of fluency, and stuttering. Most of the difficulties in pronunciation are caused by problems with the articulatory organs, in which case the articulatory organs, oral muscles and laryngeal muscles need to be treated. Secondary language disorders are mainly caused by intellectual deficiencies, hearing deficiencies and psychological disorders, and are commonly associated with mental retardation and autism.