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Amusia is a musical disorder that appears mainly as a defect in processing pitch, but it also encompasses musical memory and recognition.〔Pearce, J. M. S. (2005). "Selected observations on amusia." (). ''European Neurology'', 54(3), 145-148.〕 Two main classifications of amusia exist: acquired amusia, which occurs as a result of brain damage, and congenital amusia, which results from a music processing anomaly present since birth. Studies have shown that congenital amusia is a deficit in fine-grained pitch discrimination and that 4% of the population suffers from this disorder.〔Peretz, I., & Hyde, K. L. (2003). "What is specific to music processing? Insights from congenital amusia." (). ''Trends in Cognitive Sciences'', 7(8), 362-367.〕 Acquired amusia, on the other hand, may take several forms. Patients with brain damage may experience the loss of ability to produce musical sounds while sparing speech,〔(I. Peretz; R. Zatorre, ''Brain organization for music processing.'', Annual Review of Psychology, vol. 56, pp. 89-114 (2005) )〕 much like aphasics lose speech selectively but can sometimes still sing.〔(Hébert, S., Racette, A., Gagnon, L. & Peretz, I. (2003) Revisiting the dissociation between singing and speaking in expressive aphasia. Brain, vol. 126(8), pp. 1838-1850 )〕〔Dorgueille, C. 1966. Introduction à l'étude des amusies. Unpublished doctoral dissertation, Université de la Sorbonne, Paris.〕 Other forms of amusia may affect specific sub-processes of music processing. Current research has demonstrated dissociations between rhythm, melody, and emotional processing of music,〔Sacks, Oliver. (2007). Musicophilia, New York: Random House. pp. 3-17, 187-258, 302-303.〕 and amusia may include impairment of any combination of these skill sets. ==Basics of music processing== Neurologically intact individuals appear to be born musical. Even before they are able to talk, infants show remarkable musical abilities that are similar to those of adults in that they are sensitive to musical scales and a regular tempo.〔 Also, infants are able to differentiate between consonant and dissonant intervals. These perceptual skills indicate that music-specific predispositions exist.〔 Prolonged exposure to music develops and refines these skills. Extensive musical training does not seem to be necessary in the processing of chords and keys.〔 The development of musical competence most likely depends on the encoding of pitch along musical scales and maintaining a regular pulse, both of which are key components in the structure of music and aid in perception, memory, and performance.〔 Also, the encoding of pitch and temporal regularity are both likely to be specialized for music processing.〔 Pitch perception is absolutely crucial to processing music. The use of scales and the organization of scale tones around a central tone (called the tonic) assign particular importance to notes in the scale and cause non-scale notes to sound out of place. This enables the listener to ascertain when a wrong note is played. However, in individuals with amusia, this ability is either compromised or lost entirely.〔 Music-specific neural networks exist in the brain for a variety of music-related tasks. It has been shown that Broca's area is involved in the processing of musical syntax.〔Burkhard Maess, Stefan Koelsch, Thomas C. Gunter and Angela D. Friederici. "Musical syntax is processed in Broca’s area: an MEG study" (2001) ''Nature Publishing Group''.〕 Furthermore, brain damage can disrupt an individual's ability to tell the difference between tonal and atonal music and detect the presence of wrong notes, but can preserve the individual's ability to assess the distance between pitches and the direction of the pitch.〔 The opposite scenario can also occur, in which the individual loses pitch discrimination capabilities, but can sense and appreciate the tonal context of the work. Distinct neural networks also exist for music memories, singing, and music recognition. Neural networks for music recognition are particularly intriguing. A patient can undergo brain damage that renders him/her unable to recognize familiar melodies that are presented without words. However, the patient maintains the ability to recognize spoken lyrics or words, familiar voices, and environmental sounds.〔 The reverse case is also possible, in which the patient cannot recognize spoken words, but can still recognize familiar melodies. These situations overturn previous claims that speech recognition and music recognition share a single processing system.〔 Instead, it is clear that there are at least two distinct processing modules: one for speech and one for music.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「amusia」の詳細全文を読む スポンサード リンク
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