The Perception of Grouping Boundaries in Music

Some of the most fundamental questions in the study of music perception concern the manner in which the human perceptual system groups musical elements together. In this paper, we examine the grouping of musical elements into contiguous segments that occur sequentially in time or, to put it another way, the identification of boundaries between the final element of one segment and the first element of the subsequent one. This way of structuring a musical surface is usually referred to as grouping or segmentation and is to be distinguished from the grouping of musical elements that occur simultaneously in time, a process usually referred to as streaming (Bregman, 1990). In musical terms, the kinds of group we shall consider might correspond to motifs, phrases, sections and other aspects of musical form. Just as speech is perceptually segmented into words which subsequently provide the building blocks for the perception of phrases and complete utterances (Brent, 1999), motifs or phrases in music are identified by listeners, stored in memory and made available for inclusion in higher-level structural groups (Lerdahl & Jackendoff, 1983; Peretz, 1989; Tan et al., 1981). The low-level organisation of the musical surface into groups allows the use of these primitive perceptual units in more complex structural processing and may alleviate processing and memory demands. We restrict ourselves primarily to research on symbolic representations of musical structure that take discrete note-like events as their musical surface (Jackendoff, 1987). Research on segmentation from sub-symbolic or acoustic representations of music (e.g., Abdallah et al., 2006; Gjerdingen, 1999; Todd, 1994; Šerman & Griffith, 2004) are not discussed. Furthermore, the present work emphasises melody (although not exclusively) reflecting the predominant trends in theoretical and computational treatments of perceived grouping structure in music. Grouping structure is generally agreed to be logically independent of metrical structure (Lerdahl & Jackendoff, 1983) and some evidence for a separation between the psychological processing of the two kinds of structure has been found in cognitive neuropsychological (LiegeoiseChauvel et al., 1998; Peretz, 1990) and neuroimaging research (Brochard et al., 2000). In practice, however, metrical and grouping structure are often intimately related and both are likely to serve as inputs to the processing of more complex musical structures (Lerdahl & Jackendoff, 1983). Nonetheless, most theoretical, empirical and computational research has considered the perception of grouping structure independently of metrical structure (Stoffer, 1985 and Temperley, 2001 being notable exceptions).