diplacusis

   Also known as paracusis duplicata and double hearing. The term diplacusis comes from the Greek words diploös (double) and akouein (to hear). This translates to double sound or double hearing. The term is used as a generic term for a group of auditory distortions characterized by the hearing of a single tone at a different pitch in each ear. The American otolaryngolo-gist George Elmer Shambaugh, Sr. (1869-1947) has been credited with providing the first case report of diplacusis in 1907, attributing the condition to slight differences in response on the part of the tectorial membranes of the right and left ear. In 1940 Shambaugh's son, George Elmer Shambaugh, Jr. (1903-2008) distinguished three varieties of diplacusis which he called diplacu-sis binauralis dysharmonica, diplacusis binauralis echotica, and diplacusis monauralis dysharmon-ica. Diplacusis binauralis dysharmonica, considered the most common variant of diplacusis, is conceptualized as an auditory distortion in which a single sound is heard at a different pitch by the two ears. The ensuing dissonant double clang is attributed to the disordered processing of sounds by a diseased ear, in combination with the normal processing of sounds by the other, healthy ear. In diplacusis binauralis echotica a single sound is heard a fraction of a second later by the diseased ear. In diplacusis monauralis dysharmonica a pure tone is heard as a double tone, due to echoing within the diseased ear itself. A fourth variant, known as diplacusis qualitatis, is conceptualized as a type of diplacusis in which the diseased ear is held responsible for changing the quality of notes without altering their pitch. Diplacusis is commonly classified as a type of *paracusis (i.e. false acoustic perception). Etiologically, diplacu-sis is associated primarily with Ménière's disease and retrocochlear lesions. Beyond the context of pathology, however, cases of diplacusis on the order of 1 or 2% can be found in many individuals with normal hearing, especially under the influence of fatigue and/or exposure to noise.

   References

   Albers, G.D., Wilson, W.H. (1968). Diplacusis I. Historical review. Archives of Otolaryngology, 87, 601-603.

   Révész, G. (2001). Introduction to the psychology of music. Translated by de Courcy, G.I.C. Mineola, NY: Dover Publications.

   Shambaugh, Sr., G.E. (1907). A restudy of the minute anatomy of structures in the cochlea with conclusions bearing on the solution ofthe problem of tone perception. American Journal ofAnatomy, 7, 245-257.

   Shambaugh, Jr., G.E. (1940). Diplacusis: A localizing symptom of disease of the Organ of Corti. Archives of Otolaryngology, 31, 160-184.