Stuttering affects speech fluency through repetitions, prolongations, and blocks of speech sounds and words. It most commonly occurs between ages 2-4, 7-9, and 11-13. Stuttering can have both physiological causes related to respiration, phonation, and articulation muscles as well as psychological causes from negative emotions, teasing, and avoidance of difficult speaking situations. Treatments focus on strategies for fluent speech production and increasing confidence through meditation and positive self-talk. Several organizations provide more information on stuttering.