Vocal outbursts can be voluntary (controlled) or semi-voluntary (occurring as a response to an impulse that is largely beyond an individual's control). Involuntary (or semi-voluntary) vocal outbursts are a feature of certain neurological conditions characterized by other types of tics, such as involuntary movements. The classic example is Tourette's syndrome, but other neurological disturbances can result in vocal outbursts as well. Psychiatric conditions such as schizophrenia may have vocal outbursts as a symptom, and some people suffering from dementia or other forms of damage to the brain may display vocal outbursts in the form of uncontrolled or dysregulated speech. Alcohol and drug use can also lead to impairment of behavior and control, leading sometimes to vocal outbursts.