Monday, February 25, 2008
Global and Local Levels of Music Processing
"Discord: not to be confused with Datcord." - Anonymous
When music is perceived, the brain processes both local information as well as global information. Local information includes identifying specific intervals between pitches and discriminating durational values of sounds. Global information, on the other hand, includes identifying the overall melody and meter of a song. (Peretz and Morais, 1993; Peretz, 1990; Andrade and Bhattacharya, 2003). Researchers have found that healthy non-musicians show auditory activation patterns in the right frontotemporal cortex, whereas professional musicians showed activation in not only this same right hemispheric region but also in the left-hemispheric auditory areas. This lateralization to the left hemisphere in musicians was ascribed to the fact that musical training leads to enhanced perceptual processing of local information, which is predominately based in the left hemisphere (Schuppert et al, 2000). In patients with left-hemispheric lesions, local interval processing has been known to be disordered but global contour perception usually remains intact. In patients with right-hemisphere damage, however, both the local and global processing strategies may be disordered. (Peretz, 1990; Liegeois-Chauvel et al., 1998; Andrade and Bhattacharya, 2003). This finding suggests that global processing of melody is a prerequisite for the decoding of local pitch interval discrimination and can be thought of as a “two-stage processing cascade” (Dowling and Bartlett, 1981; Dowling, 1982; Peretz, 1993; Peretz et al 2002).
Although current studies support evidence for the location of local and global frequency information processing, there is still disagreement about the hierarchical organization of temporal information processing. While some researchers report that the overall meter of a song must be processed initially before local rhythm recognition occurs (Povel and Essens, 1985), others have found that the global and local processing occur separately (Lerdahl and Jackendoff, 1983; Peretz, 1990; Liegeois-Chauvel et al., 1998). The latter view has been supported by reports of patients having similar deficits in temporal perception regardless of the hemisphere of damage, as well as similar local rhythm and global meter deficits occurring in patients following lesions in either hemisphere (Mavlov, 1980; Fries and Swihart, 1990; Peretz, 1990; Peretz et al., 1994). Researchers are now studying possible underlying neural substrates that may cause cross-hemispheric local and global musical information processing (Schuppert et al, 2000).
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