Effects of musical expertise and boundary markers on phrase perception in music

A neural correlate for phrase boundary perception in music has recently been identified in musicians. It is called music closure positive shift ("music CPS") and has an equivalent in the perception of speech ("language CPS"). The aim of the present study was to investigate the influence of musical expertise and different phrase boundary markers on the music CPS, using event-related brain potentials (ERPs) and event-related magnetic fields (ERFs). Musicians and nonmusicians were tested while listening to binary phrased melodies. ERPs and ERFs of both subject groups differed considerably from each other. Phrased melody versions evoked an electric CPS and a magnetic CPSm in musicians, but an early negativity and a less pronounced CPSm in nonmusicians, suggesting different perceptual strategies for both subject groups. Musicians seem to process musical phrases in a structured manner similar to language. Nonmusicians, in contrast, are thought to detect primarily discontinuity in the melodic input. Variations of acoustic cues in the vicinity of the phrase boundary reveal that the CPS is influenced by a number of parameters that are considered to indicate phrasing in melodies: pause length, length of the last tone preceding the pause, and harmonic function of this last tone. This is taken as evidence that the CPS mainly reflects higher cognitive processing of phrasing, rather than mere perception of pauses. Furthermore, results suggest that the ERP and MEG methods are sensitive to different aspects within phrase perception. For both subject groups, qualitatively different ERP components (CPS and early negativity) seem to reflect a top-down activation of general but different phrasing schemata, whereas quantitatively differing MEG signals appear to reflect gradual differences in the bottom-up processing of acoustic boundary markers.