Tinnitus is the perception of noise (e.g., ringing, buzzing, hissing) in the absence of an external sound source. It may be perceived in one or both ears, centered in the head, or localized outside the head. Objective tinnitus is a rare condition in which the perceived noise is generated within the body—for example, from a muscle spasm or a vascular disorder. Sound from objective tinnitus may be detected/heard by an examiner (i.e., not only by the individual with the symptom). Subjective tinnitus, which is far more common, is perceived only by the individual with the symptom. As the impact of tinnitus on one's quality of life can vary (from minimal to severe), there is a difference between bothersome tinnitus and nonbothersome tinnitus. Several other terms are used to differentiate tinnitus within the literature, including the following examples:

· Primary tinnitus has no identified cause other than hearing loss.

· Pulsatile tinnitus is characterized by noise that is rhythmic and resembles the heartbeat.

· Secondary tinnitus has a specific known cause.

· Somatic tinnitus is caused or influenced by sensory input in the body—for example, muscle spasms.

Hyperacusis is an exaggerated response to ordinary sounds in the environment that are tolerated well by those without hyperacusis. Hyperacusis may result in a range of reactions and emotional responses to sound, varying by individual. Categories of hyperacusis include loudness, annoyance, fear, and pain (Tyler et al., 2014). As with tinnitus, hyperacusis varies in severity. The negative responses to sound may be strong enough to cause avoidance of normal interactions and situations and may significantly alter a person's life. Related terms found in descriptions of hyperacusis include the following examples:

· Decreased sound tolerance refers to various disorders involving intolerance to and avoidance of sound.

· Misophonia is characterized by a strong dislike of certain sounds, unique to the individual, that results in negative emotions and reactions.

· Phonophobia is characterized by a persistent and abnormal fear of sound.

Tinnitus and hyperacusis may exist independently or in comorbidity.