Rhythm
Perception of temporal patterns is fundamental to normal hearing, speech, motor control, and music (Grahn, 2012). Rhythm perception is considered as one of the unique abilities that human processes. Rhythmic pattern is generally indicated by the onset of a stimulus and the time between onsets as intervals. For example, in a march rhythm, every other beat is accented (1 2 1 2), whereas for a waltz it is the first of every three beats (1 2 3 1 2 3). These patterns therefore differ in their perceived meter: the strong “1” and other weak beats.

Rhythm in music represents an ordered alteration of long and short notes regardless of the absolute duration of each note (Choi, 2021). It is composed of distinct temporal components such as pattern, meter, and tempo. Meter includes the representation of recurring patterns of strong and weak beats; pattern involves the representation of varying intervals at different time points and linked hierarchically across segments; and tempo involves representing the frequency of underlying pulse structures. As an organizing structure of music, it orders the movement of musical patterns in time (Thaut et al., 2014).

In speech domain, rhythm is defined as “the perceived regularity of prominent units”. Speech rhythm represents the timing of successive vowel and consonant sequences (Hayes, 1989). Rhythm is used differently across languages. Based on rhythmical properties, languages are typically categorized as stress-timed (e.g., English), syllable-timed (e.g., Mandarin), and mora-timed (e.g., Japanese), (Ladefoged & Johnson, 2014). In stress-timed languages, stressed syllables are longer than unstressed ones and tend to occur isochronously (Zhang & Lee, 2019). Stressed syllables are produced at approximately regular intervals while unstressed syllables are often compressed to fit in the constant interval between stressed syllables (Nespor & Vogel, 2007). For syllable-timed language (e.g. Mandarin and Cantonese), syllables whether stressed or not, tend to occur with equal intervals of time, in the absence of special prosodic and pragmatic intention. Stressed syllables acoustically are not perceived stronger than unstressed ones. Mora-timed language is very similar to syllable-timed language, only that the rhythm step is divided by morae (V or CV).

Speech and music
The auditorial perception of speech and music is significantly interconnected. It is widely believed that long-term musical experience facilitates speech perception and musical training benefits the neural encoding of speech. This effect, known as music-to-language transfer, largely undergirds theoretical models of cross-domain plasticity. Recently, there is emerging evidence of language-to-music transfer. The “OPERA” Hypothesis proposed by Patel (2011) has identified five key conditions that allow such transfer of competencies between speech and music, which are Overlap, Precision, Emotion, Repetition, and Attention.
Many research had demonstrated that musicianship could influence language perception within the same mechanism. Early exploration on OPERA was mainly focusing on the pitch perception, which is believed to be fundamental to both speech and music. Neural encoding of pitch in the auditory brainstem is known to be shaped by long-term experience with language or music, implying that early sensory processing is subject to experience dependent neural plasticity (Bidelman et al., 2011). For example, the investigation conducted by Perrachione et al. (2013) provided evidence indicating potential commonalities in the neuro mechanisms underlying pitch processing in both language and music, which includes attention and working memory, subcortical sensory pathways where pre-attentive pitch signals are encoded. Also, the study by Bidelman et al. (2013) discovered that the tone-language background is associated with higher auditory perceptual performance for music listening. Other musical pitch studies using ERP(Sadakata et al., 2020), fMRI (Bradley, 2013; Li et al., 2021) also supported that pitch perception invokes similar neuro mechanism.

Neurological perspective
As another fundamental property of auditorial input, a number of approaches are used to understanding rhythm processing, incorporating methodologies based on behavior, neuroimaging, and patient studies (Nederlanden et al., 2019). Studies using fMRI involve measuring the brain’s online metabolic activity by comparing the pattern differences between two or more different experimental conditions. For rhythm perception, greater activity has been seen in the following motor structures involved in perceiving the beat, namely the basal ganglia (BG) and supplementary motor area (SMA), which are the fundamental areas in rhythm perception. The study by Chen et al. (2006) revealed the individual differences in beat perception. In comparison to weak beat perceivers, strong beat perceivers display greater activity in the supplementary motor area (SMA), ventrolateral prefrontal cortex (PFC), and medial PFC. Furthermore, strong beat perceivers displayed a more extensive distribution of brain activity across frontal and motor areas, while weak beat perceivers exhibited constrained network primarily located within auditory processing areas. The recruitment of basal ganglia (specifically, the putamen) during beat perception was further confirmed by a later fMRI study (Grahn & Rowe, 2009). Also, greater connectivity was observed between the putamen and the SMA, PMC, and auditory cortex during the musical rhythm processing.

Being a common acoustic feature, the perception of rhythm in the domain of music and of speech is proposed to be processed by overlapping brain networks. Although human responses to musical rhythm are universal, there is much we do not understand about how rhythm is processed in the brain in the linguistic and speech context. Also, it is still unknown whether there will be any unidirectional or bidirectional transfer between music and speech in the rhythm perception.

Objectives
The current study seeks to fill the research gap by investigating the language-to-music transfer of rhythm perception abilities that is modulated by the prosodic nature of native language. Specifically, this study targets at these two questions: 1) how does native languages modulate the perception of rhythm in speech and music? 2) What are the similarities and differences in brain activity between their two groups in making rhythmic judgments?

Being a stress-timed language, English has a higher vocalic interval variability than syllable-stressed languages such as Mandarin or Cantonese. English native speakers receive linguistic input with more variant time intervals in daily speech communication, which provides them with a higher ability to detect the rhythm feature in auditory stimuli and make perception on rhythms. It was reasonable to hypothesize that English native speakers/listeners would outperform Mandarin or Cantonese natives on rhythmic perception.

This experiment will use fMRI to measure functional brain activity in individuals making discrimination and judgement on rhythmic auditory patterns. Although the fMRI scanning will produce loud noises which could potentially affect the musical perception, rhythm is believed to be minorly affected by the noisy sounds. During the scanning, participants will perform a rhythm discrimination task.
By conducting the neuro experiment, this study aims to investigate the impact of rhythmic nature between time-stressed language and syllable-stresses language on rhythm perception abilities, and examine the transferability of linguistic rhythm perception abilities onto the music domain. With the help of neuro-imaging techniques, this study seeks to explore the neurocognitive mechanisms underlying English and Mandarin native speaker’s rhythm processing and perception by identifying the neural response patterns, therefore identifying the neurocognitive substrates and interactions of different brain networks that support successful rhythm perception in the relation to language.

2. Methods

Participants
30 native speakers each of Mandarin and English will be recruited to participate in this study. All participants should be university students in Hong Kong with ages ranging from 18 to 28. Participants will be required to fill in the Language History Questionnaire (LHQ) version 3 for their demographic information and linguistic background. For this project, the participants should have no musical training background. Also, they will be all right-handed, and have no hearing loss or absolute pitch ability.

Stimuli and Task
The experimental tasks included conditions in which participants discriminated the rhythmic elements of beat pattern. The Music Ear Test (Wallentin et al., 2010) will be adopted to assess participant’s musical rhythmic discrimination. The test has been validated through prior research and exhibits a strong association with other assessments of musical ability. It has been vastly used to measure musical aptitude in Eastern and Western populations (Chen et al., 2016).

The rhythm subtest contained 52 pairs of rhythmical phrases generated by 4–11 wood block beats. On each trial, two melodic phrases will be played at 100 beats per minute. The participants then will judge whether the rhythm pattern of these two melodic phrases were different. There are 26 “same” and 26 “different” trials and the maximum possible score was 52. On each “different” trial, there was one rhythmic change(Zhang et al., 2020). 31 trials contained even subdivisions of the beat whereas 21 trials contained triplets, which would result in varying rhythmic complexities across trials. Reliability analysis showed a fair internal consistency of the rhythm subtest (Cronbach’s α = 0.64) (Choi, 2021).

fMRI scanning
The fMRI scanning will acquire the brain activity underlying the rhythm perception procedure.
During the fMRI scanning session, participants will be comfortably positioned inside the MRI scanner and provided with noise-cancelling earplugs and headphones to ensure optimal sound perception. To minimize head motion artifacts, foam padding or head stabilizers will be used. To perform the judgement task, two keyboard controllers will be provided for participants to press the button to indicate “same” or “different”.
Before the task, the structure of the brain will be scanned to localize the region of interest. The procedure of experiment, including the instructions of experiment flow, presentation of stimuli, and the judgement task will be achieved with E-Prime. Auditory stimuli of rhythm perception will be presented to participants through the headphones while they are inside the scanner. The entire procedure of perception and judgement task will be recorded with functional scanning. Whole-brain functional images will be collected using blood-oxygen-level-dependent (BOLD) contrast imaging. Stimulus presentation and response recording will be synchronized of timestamps with the MRI scanner using a stim tracker.
After the experiment procedure with functional scanning, T1 weighted scans, resting-state functional scan and lastly the diffusion tenser imaging will be conducted. T1 scanning allows a better resolution to the brain structure. The resting stage scan provides the blood-oxygen-level-dependent in the absence of explicit stimuli or tasks, which serve as a baseline or reference scan for comparison to make subtractions to isolate the brain activation induced by experimental stimuli. DTI allows us to examine the structural connectivity of white matter pathways in the brain, which could be indicators on the investigation on the cortical connection between different areas involved in rhythm perception.