Tinnitus activity in the limbic system and autonomic nervous system, thus increasing tinnitus awareness and annoyance. There are two types of tinnitus: "subjective tinnitus" and "objective tinnitus". Tinnitus is usually subjective, meaning that there is no sound detectable by other means. Subjective tinnitus has also been called "tinnitus aurium", "non-auditory" or "non-vibratory" tinnitus. In very rare cases tinnitus can be heard by someone else using a stethoscope, and in less rare – but still uncommon – cases it can be measured as a spontaneous otoacoustic emission (SOAE) in the ear canal. In such cases it is objective tinnitus, also called "pseudo-tinnitus"
Tinnitus retraining therapy large proportion of dropouts; reported 'success' ratios may not take these subjects into account. There are few available studies, but most show that tinnitus naturally declines over time (years) in a large proportion of subjects surveyed, without any treatment. The annoyance of tinnitus also tends to decline over time. In at least some, tinnitus spontaneously disappears. A Cochrane review found only one sufficiently rigorous study of TRT and noted that while the study suggested benefit in the treatment of tinnitus, the study quality was not good enough to draw firm conclusions. A separate Cochrane review of sound therapy (though they