Tinnitus is an abnormal noise in the ear. About six percent of the general population suffers from what they consider to be "severe" tinnitus. Tinnitus can come and go, or be continuous. It can sound like a low roar, or a high-pitched ring. Tinnitus may be bilateral or unilateral. The causes of tinnitus are various, e.g., inner ear injury, 8th nerve lesion, injury of the brainstem, and rarely of the brain. There also are many extracranial causes of tinnitus. Upon making the diagnosis of tinnitus, medical therapy may occasionally help lessen the noise even though the cause has not been identified. Current therapy for tinnitus, so-called tinnitus retraining therapy, first includes learning about what does actually cause the tinnitus. This process is called habituation of reaction. Tinnitus then becomes quieter for long period of time and may eventually disappear, or becomes part of the background .sound of silence (habituation of perception). In some cases, changes in the inner ear function may be important in triggering the occurrence of tinnitus (e.g., Meniere's disease or acute acoustic trauma); however, the retraining approach works independently of the triggering factor. Despite the importance of hearing loss, a recent study in tinnitus patients showed that there was no significant difference in hearing between the tinnitus group and control group of healthy subjects.