Disorders characterized by recurrent tics that may interfere with speech and other activities. tics are sudden, rapid, nonrhythmic, stereotyped motor movements or vocalizations which may be exacerbated by stress and are generally attenuated during absorbing activities. tic disorders are distinguished from conditions which feature other types of abnormal movements that may accompany another another condition. (from dsm-iv, 1994)

A tic is a sudden and repetitive motor movement or vocalization that is not rhythmic and involves discrete muscle groups. Tics are typically brief and may resemble a normal behavioral characteristic or gesture. Tics can be invisible to the observer, such as abdominal tensing or toe crunching...