The occurrence of MES has been suggested to be very high among the hearing impaired through acquired deafness or the ear condition known as tinnitus. Though exact causation is uncertain, it has been theorized that the "release phenomenon" is taken into effect. The "release phenomenon" says that individuals with acquired deafness may experience musical hallucinations because the lack of stimulation, which can give room for the brain to interpret internal sounds as being external.

Sufferers typically hear music or singing and the condition is more common in women. The hallucinatory experiences differ from that commonly experienced in psychotic disorders although there may be some overlap. The most important distinction is the realization that the hallucinations are not real. Delusional beliefs associated with the hallucinations may occur, but some degree of insight should be preserved. There should not be any other psychotic symptoms present, especially hallucinations in other modalities.

Musical ear syndrome (MES) describes a condition seen in people who have hearing loss and subsequently develop auditory hallucinations. "MES" has also been associated with musical hallucinations, which is a complex form of auditory hallucinations where an individual may experience music or sounds that are heard without an external source. It is comparable to Charles Bonnet syndrome (visual hallucinations in visually impaired people) and some have suggested this phenomenon could be included under this diagnosis.

A paracusia, or auditory hallucination, is a form of hallucination that involves perceiving sounds without auditory stimulus.

A common form of auditory hallucination involves hearing one or more talking voices. This may be associated with psychotic disorders, and holds special significance in diagnosing these conditions. However, individuals without any psychiatric disease whatsoever may hear voices.

There are three main categories into which the hearing of talking voices often fall: a person hearing a voice speak one's thoughts, a person hearing one or more voices arguing, or a person hearing a voice narrating his/her own actions. These three categories do not account for all types of auditory hallucinations.

Other types of auditory hallucination include exploding head syndrome and musical ear syndrome. In the latter, people will hear music playing in their mind, usually songs they are familiar with. This can be caused by: lesions on the brain stem (often resulting from a stroke); also, sleep disorders such as narcolepsy, tumors, encephalitis, or abscesses. This should be distinguished from the commonly experienced phenomenon of getting a song stuck in one's head. Reports have also mentioned that it is also possible to get musical hallucinations from listening to music for long periods of time. Other reasons include hearing loss and epileptic activity.

In the past, the cause of auditory hallucinations has been attributed to cognitive suppression by way of executive function failure of the fronto-parietal sulcus. Newer research has found that they coincide with the left superior temporal gyrus, suggesting that they are better attributed to speech misrepresentations. It is assumed through research that the neural pathways involved in normal speech perception and production, which are lateralized to the left temporal lobe, also underlie auditory hallucinations . Auditory hallucinations correspond with spontaneous neural activity of the left temporal lobe, and the subsequent primary auditory cortex. The perception of auditory hallucinations correspond to the experience of actual external hearing, despite the absence of physical acoustic output .

Investigators have successfully narrowed down the major factors that are associated with musical hallucinations. Evers and Ellgers compiled a significant portion of musical hallucination articles, case studies etc. and were able to categorize five major etiologies:

- Hypoacusis

- Psychiatric disorders

- Focal brain lesion

- Epilepsy

- Intoxication

In 73 individual cases reviewed by Evers and Ellger, 57 patients heard tunes that were familiar, while 5 heard unfamiliar tunes. These tunes ranged from religious pieces to childhood favorites, and also included popular songs from the radio. Vocal and instrumental forms of classical music were also identified in some patients. Keshavan found that the consistent feature of musical hallucinations was that it represented a personal memory trace. Memory traces refer to anything that may seem familiar to the patient, which indicated why certain childhood or familiar songs were heard.

Patients with unilateral hearing loss have difficulty in

- hearing conversation on their impaired side

- localizing sound

- understanding speech in the presence of background noise.

- interpersonal and social relations

- difficulty concentrating in large, open environments

In quiet conditions, speech discrimination is no worse than normal hearing in those with partial deafness; however, in noisy environments speech discrimination is almost always severe.

Unilateral hearing loss (UHL) or single-sided deafness (SSD) is a type of hearing impairment where there is normal hearing in one ear and impaired hearing in the other ear.

Cortical deafness is a rare form of sensorineural hearing loss caused by damage to the primary auditory cortex. Cortical deafness is an auditory disorder where the patient is unable to hear sounds but has no apparent damage to the anatomy of the ear (see auditory system), which can be thought of as the combination of auditory verbal agnosia and auditory agnosia. Patients with cortical deafness cannot hear any sounds, that is, they are not aware of sounds including non-speech, voices, and speech sounds. Although patients appear and feel completely deaf, they can still exhibit some reflex responses such as turning their head towards a loud sound.

Cortical deafness is caused by bilateral cortical lesions in the primary auditory cortex located in the temporal lobes of the brain. The ascending auditory pathways are damaged, causing a loss of perception of sound. Inner ear functions, however, remains intact. Cortical deafness is most often cause by stroke, but can also result from brain injury or birth defects. More specifically, a common cause is bilateral embolic stroke to the area of Heschl's gyri. Cortical deafness is extremely rare, with only twelve reported cases. Each case has a distinct context and different rates of recovery.

It is thought that cortical deafness could be a part of a spectrum of an overall cortical hearing disorder. In some cases, patients with cortical deafness have had recovery of some hearing function, resulting in partial auditory deficits such as auditory verbal agnosia. This syndrome might be difficult to distinguish from a bilateral temporal lesion such as described above.

Spatial hearing loss, refers to a form of deafness that is an inability to use spatial cues about where a sound originates from in space. This in turn affects the ability to understand speech in the presence of background noise.

Neuroscientists have learned a lot about the role of the brain in numerous cognitive mechanisms by understanding corresponding disorders. Similarly, neuroscientists have come to learn a lot about music cognition by studying music-specific disorders. Even though music is most often viewed from a "historical perspective rather than a biological one" music has significantly gained the attention of neuroscientists all around the world. For many centuries music has been strongly associated with art and culture. The reason for this increased interest in music is because it "provides a tool to study numerous aspects of neuroscience, from motor skill learning to emotion".

In 2015 a small survey reported voice hearing in persons with a wide variety of DSM-5 diagnoses, including:

- Bipolar disorder

- Borderline personality disorder

- Depression (mixed)

- Dissociative identity disorder

- Generalized anxiety disorder

- Major depression

- Obsessive compulsive disorder

- Post-traumatic stress disorder

- Psychosis (NOS)

- Schizoaffective disorder

- Schizophrenia

However, numerous persons surveyed reported no diagnosis. In his popular 2012 book "Hallucinations", neurologist Oliver Sacks describes voice hearing in patients with a wide variety of medical conditions, as well as his own personal experience of hearing voices.

Beat deafness is a form of congenital amusia characterized by a person's inability to distinguish musical rhythm or move in time to it.

An individual with this condition has an especially difficult time maintaining a steady beat, and even has difficulty following along to a steady rhythm. Before it was a known disorder, it was thought that these individuals were just severely uncoordinated, and therefore were unable to follow along with the music. It has been discovered recently that problems with rhythm in Schizophrenia, Parkinson's, and Attention Deficit Hyperactive Disorder are also found to have a correlation to rhythm deficiencies.

Auditory arrhythmia is the inability to rhythmically perform music, to keep time, and to replicate musical or rhythmic patterns. It has been caused by damage to the cerebrum or rewiring of the brain.

In hyperacusis, the symptoms are ear pain, annoyance, and general intolerance to many sounds that most people are unaffected by. Crying spells or panic attacks may result from the experience of hyperacusis. It may affect either or both ears. Hyperacusis can also be accompanied by tinnitus. Hyperacusis can result in anxiety, stress and phonophobia. Avoidant behaviour is often a response to prevent the effects of hyperacusis and this can include avoiding social situations.

SSHL is diagnosed via pure tone audiometry. If the test shows a loss of at least 30db in three adjacent frequencies, the hearing loss is diagnosed as SSHL. For example, a hearing loss of 30db would make conversational speech sound more like a whisper.

Hyperacusis (or hyperacousis) is a debilitating hearing disorder characterized by an increased sensitivity to certain frequencies and volume ranges of sound (a collapsed tolerance to usual environmental sound). A person with severe hyperacusis has difficulty tolerating everyday sounds, some of which may seem unpleasantly or painfully loud to that person but not to others.

"Hyperacusis" is often coincident with tinnitus. Both conditions have a prevalence of about 10–15% and hearing loss as a major risk factor. However, there also appear to be important differences between the mechanisms involved in tinnitus and hyperacusis.

A hallucination is a perception in the absence of external stimulus that has qualities of real perception. Hallucinations are vivid, substantial, and are perceived to be located in external objective space. They are distinguishable from several related phenomena, such as dreaming, which does not involve wakefulness; pseudohallucination, which does not mimic real perception, and is accurately perceived as unreal; illusion, which involves distorted or misinterpreted real perception; and imagery, which does not mimic real perception and is under voluntary control. Hallucinations also differ from "delusional perceptions", in which a correctly sensed and interpreted stimulus (i.e., a real perception) is given some additional (and typically absurd) significance.

Hallucinations can occur in any sensory modality—visual, auditory, olfactory, gustatory, tactile, proprioceptive, equilibrioceptive, nociceptive, thermoceptive and chronoceptive.

A mild form of hallucination is known as a "disturbance", and can occur in most of the senses above. These may be things like seeing movement in peripheral vision, or hearing faint noises and/or voices. Auditory hallucinations are very common in schizophrenia. They may be benevolent (telling the subject good things about themselves) or malicious, cursing the subject, etc. Auditory hallucinations of the malicious type are frequently heard, for example people talking about the subject behind his/her back. Like auditory hallucinations, the source of the visual counterpart can also be behind the subject's back. Their visual counterpart is the feeling of being looked or stared at, usually with malicious intent. Frequently, auditory hallucinations and their visual counterpart are experienced by the subject together.

Hypnagogic hallucinations and hypnopompic hallucinations are considered normal phenomena. Hypnagogic hallucinations can occur as one is falling asleep and hypnopompic hallucinations occur when one is waking up. Hallucinations can be associated with drug use (particularly deliriants), sleep deprivation, psychosis, neurological disorders, and delirium tremens.

The word "hallucination" itself was introduced into the English language by the 17th century physician Sir Thomas Browne in 1646 from the derivation of the Latin word "alucinari" meaning to wander in the mind. For Browne, hallucination means a sort of vision that is "depraved and receive[s] its objects erroneously".

Many people notice that they have SSHL when they wake up in the morning. Others first notice it when they try to use the deafened ear, such as when they use a phone. Still others notice a loud, alarming "pop" just before their hearing disappears. People with sudden deafness often become dizzy, have ringing in their ears (tinnitus), or both.

Hearing loss is sensory, but may have accompanying symptoms:

- pain or pressure in the ears

- a blocked feeling

There may also be accompanying secondary symptoms:

- hyperacusis, heightened sensitivity to certain volumes and frequencies of sound, sometimes resulting from "recruitment"

- tinnitus, ringing, buzzing, hissing or other sounds in the ear when no external sound is present

- vertigo and disequilibrium

- tympanophonia, abnormal hearing of one's own voice and respiratory sounds, usually as a result of a patulous eustachian tube or dehiscent superior semicircular canals

- disturbances of facial movement (indicating possible tumour or stroke)

Superior canal (SCD) can affect both hearing and balance to different extents in different people.

Symptoms of SCDS include:

- Autophony – person's own speech or other self-generated noises (e.g. heartbeat, eye movements, creaking joints, chewing) are heard unusually loudly in the affected ear

- Dizziness/ vertigo/ chronic disequilibrium caused by the dysfunction of the superior semicircular canal

- Tullio phenomenon – sound-induced vertigo, disequilibrium or dizziness, nystagmus and oscillopsia

- Pulse-synchronous oscillopsia

- Hyperacusis – the over-sensitivity to sound

- Low-frequency conductive hearing loss

- A feeling of fullness in the affected ear

- Pulsatile tinnitus

- Brain fog

- Fatigue

- Headache/migraine

- Tinnitus – high pitched ringing in the ear

Human hearing extends in frequency from 20-20,000 Hz, and in amplitude from 0 dB to 130 dB or more. 0 dB does not represent absence of sound, but rather the softest sound an average unimpaired human ear can hear; some people can hear down to -5 or even -10 dB. 130 dB represents the threshold of pain. But the ear doesn't hear all frequencies equally well; hearing sensitivity peaks around 3000 Hz. There are many qualities of human hearing besides frequency range and amplitude that can't easily be measured quantitatively. But for many practical purposes, normative hearing is defined by a frequency versus amplitude graph, or audiogram, charting sensitivity thresholds of hearing at defined frequencies. Because of the cumulative impact of age and exposure to noise and other acoustic insults, 'typical' hearing may not be normative.

Generally, humans have the ability to hear musical beat and rhythm beginning in infancy. Some people, however, are unable to identify beat and rhythm of music, suffering from what is known as beat deafness. Beat deafness is a newly discovered form of congenital amusia, in which people lack the ability to identify or “hear” the beat in a piece of music. Unlike most hearing impairments in which an individual is unable to hear any sort of sound stimuli, those with beat deafness are generally able to hear normally, but unable to identify beat and rhythm in music. Those with beat deafness are also unable to dance in step to any type of music. Even people who do not dance well can at least coordinate their movements to the song they are listening to, because they can easily keep time to the beat.

Since cortical deafness and auditory agnosia have many similarities, diagnosing the disorder proves to be difficult. Bilateral lesions near the primary auditory cortex in the temporal lobe are important criteria. Cortical deafness requires demonstration that brainstem auditory responses are

normal, but cortical evoked potentials are impaired. Brainstem auditory evoked potentials (BAEP), also referred to as brainstem auditory evoked responses (BAER) show the neuronal activity in the auditory nerve, cochlear nucleus, superior olive, and inferior colliculus of the brainstem. They typically have a response latency of no more than six milliseconds with an amplitude of approximately one microvolt. The latency of the responses gives critical information: if cortical deafness is applicable, LLR (long-latency responses) are completely abolished and MLR (middle latency responses) are either abolished or significantly impaired. In auditory agnosia, LLRs and MLRs are preserved.

Another important aspect of cortical deafness that is often overlooked is that patients "feel" deaf. They are aware of their inability to hear environmental sounds, non-speech and speech sounds. Patients with auditory agnosia can be unaware of their deficit, and insist that they are not deaf. Verbal deafness and auditory agnosia are disorders of a selective, perceptive and associative nature whereas cortical deafness relies on the anatomic and functional disconnection of the auditory cortex from acoustic impulses.

Problems with balance can occur when there is a disruption in any of the vestibular, visual, or proprioceptive systems. Abnormalities in balance function may indicate a wide range of pathologies from causes like inner ear disorders, low blood pressure, brain tumors, and brain injury including stroke.

Many different terms are often used for dizziness, including lightheaded, floating, woozy, giddy, confused, helpless, or fuzzy. Vertigo, Disequilibrium and pre-syncope are the terms in use by most physicians and have more precise definitions.

Vertigo

Vertigo is the sensation of spinning or having the room spin about you. Most people find vertigo very disturbing and report associated nausea and vomiting.

Disequilibrium

Disequilibrium is the sensation of being off balance, and is most often characterized by frequent falls in a specific direction. This condition is not often associated with nausea or vomiting.

Presyncope

Pre-syncope is a feeling of lightheadedness or simply feeling faint. Syncope, by contrast, is actually fainting. A circulatory system deficiency, such as low blood pressure, can contribute to a feeling of dizziness when one suddenly stands up.

Problems in the skeletal or visual systems, such as arthritis or eye muscle imbalance, may also cause balance problems.