Diplacusis, also known as diplacusis binauralis, binauralis disharmonica or interaural pitch difference (IPD), is a hearing disorder whereby a single auditory stimulus is perceived as different pitches between ears. It is typically experienced as a secondary symptom of sensorineural hearing loss, although not all patients with sensorineural hearing loss experience diplacusis or tinnitus. [1] [2] The onset is usually spontaneous and can occur following an acoustic trauma, for example an explosive noise, or in the presence of an ear infection. [3] Sufferers may experience the effect permanently, or it may resolve on its own. Diplacusis can be particularly disruptive to individuals working within fields requiring acute audition, such as musicians, sound engineers or performing artists. [4] [5] [6] [7]
The term diplacusis has been used in cases which people with unilateral cochlear hearing losses or asymmetrical hearing losses, the same tone presented alternately to the two ears may be perceived as having different pitches in the two ears. [8] [9] The magnitude of the shift can be measured by getting the subject to adjust the frequency of a tone in one ear until its pitch matches that of the tone in the other ear. On presentation of a single tone alternating between ears (i.e. 1000 Hz left, 1000 Hz right, 1000 Hz left, ...), a given person will consistently mismatch these sinusoids the same amount between trials if doing a pitch-matching task. For example, a 1000 Hz tone in an unaffected ear may be heard as a slightly different pitch in the opposite ear, or have an imperfect tonal quality in the affected ear.
There are two theories on the cause of diplacusis: place theory and temporal theory. [10] Place theory posits that the cause is looking for the edge of the wave for the pitch and could explain diplacusis as a small differences between the two cochleas. [11]
Temporal theory posits that the cause is from looking at the phase locking to tell what the pitch is. This theory has a difficult time explaining diplacusis. There are some examples of pitch which do not have an "edge" on the basilar membrane, which this would account for—e.g., white noise, clicks, etc. [11] Both theories are under debate. [12] [13]
Normal human ears can discriminate between two frequencies that differ by as little as 0.2%. [14] If one ear has normal thresholds while the other has sensorineural hearing loss (SNHL), diplacusis may be present, as much as 15–20% (for example 200 Hz one ear => 240 Hz in the other).[ citation needed ] The pitch may be difficult to match because the SNHL ear hears the sound "fuzzy". Bilateral SNHL gives less diplacusis, but pitch distortions may persist. This may cause problems with music and speech understanding.
Treatment of diplacusis includes a full medical and audiological examination that may explain the nature of the problem. If needed, amplification may relieve the symptoms of diplacusis. Therapy in helping the patient understand the cause of the symptom and tinnitus retraining may provide some relief. In at least some cases, amplification makes no difference and there is no treatment other than waiting for natural resolution. Some individuals may find the provided amplification also increases the audibility of their pitch discrepancy. If onset is linked to an underlying medical cause, i.e. sudden sensorineural hearing loss, appropriate medical treatment is recommended.
Diplacusis is from the Greek words "diplous" (double) and "akousis" (hearing). [15]
Pitch is a perceptual property of sounds that allows their ordering on a frequency-related scale, or more commonly, pitch is the quality that makes it possible to judge sounds as "higher" and "lower" in the sense associated with musical melodies. Pitch is a major auditory attribute of musical tones, along with duration, loudness, and timbre.
Tinnitus is a variety of sound that is heard when no corresponding external sound is present. Nearly everyone experiences faint "normal tinnitus" in a completely quiet room; but it is of concern only if it is bothersome, interferes with normal hearing, or is associated with other problems. The word tinnitus comes from the Latin tinnire, "to ring". In some people, it interferes with concentration, and can be associated with anxiety and depression.
The vestibulocochlear nerve or auditory vestibular nerve, also known as the eighth cranial nerve, cranial nerve VIII, or simply CN VIII, is a cranial nerve that transmits sound and equilibrium (balance) information from the inner ear to the brain. Through olivocochlear fibers, it also transmits motor and modulatory information from the superior olivary complex in the brainstem to the cochlea.
Otosclerosis is a condition of the middle ear where portions of the dense enchondral layer of the bony labyrinth remodel into one or more lesions of irregularly-laid spongy bone. As the lesions reach the stapes the bone is resorbed, then hardened (sclerotized), which limits its movement and results in hearing loss, tinnitus, vertigo or a combination of symptoms. The term otosclerosis is something of a misnomer: much of the clinical course is characterized by lucent rather than sclerotic bony changes, so the disease is also known as otospongiosis.
The pitch being perceived with the first harmonic being absent in the waveform is called the missing fundamental phenomenon. The brain perceives the pitch of a tone not only by its fundamental frequency, but also by the periodicity implied by the relationship between the higher harmonics; we may perceive the same pitch even if the fundamental frequency is missing from a tone.
A hearing test provides an evaluation of the sensitivity of a person's sense of hearing and is most often performed by an audiologist using an audiometer. An audiometer is used to determine a person's hearing sensitivity at different frequencies. There are other hearing tests as well, e.g., Weber test and Rinne test.
Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear, sensory organ, or the vestibulocochlear nerve. SNHL accounts for about 90% of reported hearing loss. SNHL is usually permanent and can be mild, moderate, severe, profound, or total. Various other descriptors can be used depending on the shape of the audiogram, such as high frequency, low frequency, U-shaped, notched, peaked, or flat.
An otoacoustic emission (OAE) is a sound that is generated from within the inner ear. Having been predicted by Austrian astrophysicist Thomas Gold in 1948, its existence was first demonstrated experimentally by British physicist David Kemp in 1978, and otoacoustic emissions have since been shown to arise through a number of different cellular and mechanical causes within the inner ear. Studies have shown that OAEs disappear after the inner ear has been damaged, so OAEs are often used in the laboratory and the clinic as a measure of inner ear health.
Presbycusis, or age-related hearing loss, is the cumulative effect of aging on hearing. It is a progressive and irreversible bilateral symmetrical age-related sensorineural hearing loss resulting from degeneration of the cochlea or associated structures of the inner ear or auditory nerves. The hearing loss is most marked at higher frequencies. Hearing loss that accumulates with age but is caused by factors other than normal aging is not presbycusis, although differentiating the individual effects of distinct causes of hearing loss can be difficult.
Volley theory states that groups of neurons of the auditory system respond to a sound by firing action potentials slightly out of phase with one another so that when combined, a greater frequency of sound can be encoded and sent to the brain to be analyzed. The theory was proposed by Ernest Wever and Charles Bray in 1930 as a supplement to the frequency theory of hearing. It was later discovered that this only occurs in response to sounds that are about 500 Hz to 5000 Hz.
The temporal theory of hearing, also called frequency theory or timing theory, states that human perception of sound depends on temporal patterns with which neurons respond to sound in the cochlea. Therefore, in this theory, the pitch of a pure tone is determined by the period of neuron firing patterns—either of single neurons, or groups as described by the volley theory. Temporal theory competes with the place theory of hearing, which instead states that pitch is signaled according to the locations of vibrations along the basilar membrane.
Noise health effects are the physical and psychological health consequences of regular exposure to consistent elevated sound levels. Noise from traffic, in particular, is considered by the World Health Organization to be one of the worst environmental stressors for humans, second only to air pollution. Elevated workplace or environmental noise can cause hearing impairment, tinnitus, hypertension, ischemic heart disease, annoyance, and sleep disturbance. Changes in the immune system and birth defects have been also attributed to noise exposure.
Ultrasonic hearing is a recognised auditory effect which allows humans to perceive sounds of a much higher frequency than would ordinarily be audible using the inner ear, usually by stimulation of the base of the cochlea through bone conduction. Normal human hearing is recognised as having an upper bound of 15–28 kHz, depending on the person.
Pure-tone audiometry is the main hearing test used to identify hearing threshold levels of an individual, enabling determination of the degree, type and configuration of a hearing loss and thus providing a basis for diagnosis and management. Pure-tone audiometry is a subjective, behavioural measurement of a hearing threshold, as it relies on patient responses to pure tone stimuli. Therefore, pure-tone audiometry is only used on adults and children old enough to cooperate with the test procedure. As with most clinical tests, standardized calibration of the test environment, the equipment and the stimuli is needed before testing proceeds. Pure-tone audiometry only measures audibility thresholds, rather than other aspects of hearing such as sound localization and speech recognition. However, there are benefits to using pure-tone audiometry over other forms of hearing test, such as click auditory brainstem response (ABR). Pure-tone audiometry provides ear specific thresholds, and uses frequency specific pure tones to give place specific responses, so that the configuration of a hearing loss can be identified. As pure-tone audiometry uses both air and bone conduction audiometry, the type of loss can also be identified via the air-bone gap. Although pure-tone audiometry has many clinical benefits, it is not perfect at identifying all losses, such as ‘dead regions’ of the cochlea and neuropathies such as auditory processing disorder (APD). This raises the question of whether or not audiograms accurately predict someone's perceived degree of disability.
Psychoacoustics is the branch of psychophysics involving the scientific study of sound perception and audiology—how the human auditory system perceives various sounds. More specifically, it is the branch of science studying the psychological responses associated with sound. Psychoacoustics is an interdisciplinary field including psychology, acoustics, electronic engineering, physics, biology, physiology, and computer science.
Acoustic trauma is the sustainment of an injury to the eardrum as a result of a very loud noise. Its scope usually covers loud noises with a short duration, such as an explosion, gunshot or a burst of loud shouting. Quieter sounds that are concentrated in a narrow frequency may also cause damage to specific frequency receptors. The range of severity can vary from pain to hearing loss.
Temporal envelope (ENV) and temporal fine structure (TFS) are changes in the amplitude and frequency of sound perceived by humans over time. These temporal changes are responsible for several aspects of auditory perception, including loudness, pitch and timbre perception and spatial hearing.
Brian C.J. Moore FMedSci, FRS is an Emeritus Professor of Auditory Perception in the University of Cambridge and an Emeritus Fellow of Wolfson College, Cambridge. His research focuses on psychoacoustics, audiology, and the development and assessment of hearing aids.
Christian Lorenzi is Professor of Experimental Psychology at École Normale Supérieure in Paris, France, where he has been Director of the Department of Cognitive Studies and Director of Scientific Studies until. Lorenzi works on auditory perception.
Deniz Başkent is a Turkish-born Dutch auditory scientist who works on auditory perception. As of 2018, she is Professor of Audiology at the University Medical Center Groningen, Netherlands.