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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 Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear, sensory organ (cochlea and associated structures), or the vestibulocochlear nerve (Cranial nerves, cranial nerve VIII). SNHL accounts for a ...
, although not all patients with sensorineural hearing loss experience diplacusis or
tinnitus Tinnitus is a condition when a person hears a ringing sound or a different variety of sound when no corresponding external sound is present and other people cannot hear it. Nearly everyone experiences faint "normal tinnitus" in a completely ...
. 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. 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.


Diplacusis of pure tones

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. 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.


Biological explanation via theories of pitch of pure tones

There are two theories on the cause of diplacusis: place theory and temporal theory. 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. 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. Both theories are under debate.


Effects of sensorineural hearing loss

Normal human ears can discriminate between two frequencies that differ by as little as 0.2%. 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). 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

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.


Etymology

Diplacusis is from the Greek words "diplous" (double) and "akousis" (hearing).


See also

*
Audiology Audiology (from Latin 'to hear'; and from Ancient Greek, Greek branch of learning , ''wikt:-logia, -logia'') is a branch of science that studies hearing, balance, and related disorders. Audiologists treat those with hearing loss and proactivel ...
* Health problems of musicians *
Hearing Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is auditory sci ...
*
Hearing loss Hearing loss is a partial or total inability to hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to acquire spo ...
* Pitch (psychophysics) *
Auditory system The auditory system is the sensory system for the sense of hearing. It includes both the ear, sensory organs (the ears) and the auditory parts of the sensory system. System overview The outer ear funnels sound vibrations to the eardrum, incre ...
*
Safe listening Safe listening is a Conceptual framework, framework for health promotion actions to ensure that sound-related recreational activities (such as Concert, concerts, nightclubs, and listening to music, broadcasts, or podcasts) do not pose a risk to ...


External sources

* Diplacusis: I. Historical Review{{Cite journal, last1=Albers, first1=G. D., last2=Wilson, first2=W. H., date=1968, title=Diplacusis. I. Historical review, journal=Archives of Otolaryngology, volume=87, issue=6, pages=601–603 contd, doi=10.1001/archotol.1968.00760060603009, issn=0003-9977, pmid=4871882 *Turner, Christopher. "Perception of Pitch." Wendell Johnson Speech and Hearing Center, Iowa City. Dec. 2008. *Plack et al. (ed.). Pitch : Neural coding and perception. Springer. 2005.
Diplacusis.com
- discussion with skew graphs


References

Pitch (music) Psychoacoustics Audiology Hearing loss