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