Neural correlates of beat and metre perception: the role of the inferior frontal gyrus
MetadataShow full item record
Temporal regularity and metrical organisation are important factors in beat and metre perception. The current thesis aims to investigate neural correlates of beat and metre perception in healthy non-musician volunteers, using functional magnetic resonance imaging (fMRI). In particular, the thesis focuses on determining the role of the Inferior Frontal Gyrus (IFG, in particular BA44/45) in beat and metre perception. The IFG has been proposed to be involved in higher order cognitive processes during various temporal sequencing, such as speech, movement, and music. Previous studies have shown that the temporal processing of rhythm activates auditory and sensorimotor areas, but the role of the IFG in rhythm perception has not yet been fully understood. Study 1 investigated beat perception in complex rhythms, in which the addition of volume accents either enhanced or weakened the beat perception, resulting in Unaccented, Beat Accented or Non-Beat Accented rhythms. Participants (N=14; 6 males) listened to rhythm pairs across all three conditions, and judged whether each rhythm pair was the same or different. Results showed that left IFG activation (BA44) was significantly greater during the Non-Beat Accented condition compared to Beat Accented condition, whereas the right IFG activation showed no significant difference between the two conditions. Study 2 investigated metre perception of a series of isochronous sequences, of which metrical organisation was grouped by 2/4 (C2), 3/4 (C3), or 4/4 (C4) using pitch accents, or remained without metrical grouping (or 1/4, C1). The same participants (N=15; 6 males) listened to the stimuli and indicated the perceived metrical grouping level. Results showed that the activation of bilateral IFG parametrically increased from C2 to C3 to C4. Interestingly, the activation was found to be significantly greater in C1 relative to C2, suggesting that involuntary subjective in C1 may increase the brain response. Converging results from both Study 1 and Study 2 demonstrated, firstly, that the bilateral IFG is involved in rhythm perception in addition to the auditory and sensorimotor areas, including primary and secondary auditory areas, supplementary motor areas, premotor areas, insula, and basal ganglia. Secondly, the left IFG (BA44) in particular was significantly modulated by the rhythmic complexity relating to both temporal regularity and metrical organisation, while showing the suppression during the Beat Accented rhythm condition of Study 1 and the binary pattern (C2) of Study 2. This thesis argues that the left IFG (BA44) may have the role the higher order cognitive processing, such as attention and prediction, in the perception of hierarchical structures in metric rhythms.