Temporal relationship between dancer’s body movements and music beats in classical ballet

Musicality is one of the most essential aspects of dance performance: Dancers control their bodies to the music, and audiences appreciate dances beautifully harmonized with music. The present study explores this problem from the perspective of synchronization between music beats and body movements. Specifically, we investigated the temporal relationship between dancer’s body movements and metronome beats when a dancer performed four basic classical ballet movements (i.e., changement, passé, jeté, and tendu) to the metronome. We measured body movements of 10 ballet dancers using an optical motion capture system and force plates, and analyzed what movement reference points of dancer’s body motion (e.g., movement endpoints and ground reaction force peaks) occurred on or close to the beat and backbeat. Specific reference points coincided with the beat timing common to most dancers, but the different reference points were synchronized with the beat depending on the movements. These reference points were consistent with those reported in previous studies of the temporal relationship between music and body movements. Therefore, the present result suggests that humans have a set of common movement features that can serve as reference points for music-motion synchronization, and dancers select appropriate ones according to the target movements.

Methods
Appratus and signal processing
We measured the dancer’s body movement using an optical motion capture system (Vicon Nexus) at a frame rate of 250 Hz. Retroreflective markers were attached to 35 body sites using a plug-in full-body gait model. Ground reaction force (GRF) was measured using a force plate (Kistler Instruments) at a sampling rate of 1 KHz via external analog inputs to the Vicon system. Motion data were filtered with a 4th-order zero-phase low-pass filter (cutoff frequency: 50 Hz), and velocity and acceleration were calculated using numerical derivatives. GRF data were filtered with a 4th-order zero-phase low-pass filter (cutoff frequency: 400 Hz). Positional data are expressed in xyz coordinates, where the x-axis represents the front-back direction (positive towards the back), the y-axis represents the left-right direction (positive towards the right), and the z-axis represents the up-down direction (positive upwards). 

Task and procedure
The participant’s task was to perform the specified ballet movements in sync with the metronome’s rhythm. The target movements were changement, passé, jeté (outward), and tendu (outward). The metronome's tempo was set to 60 beat per minute (bpm) for passé, jetés, and tendus, and 80 bpm for changements. Participants repeated the movements at least 16 times for changements and 24 times for the other movements. We discarded the first several cycles of motion data and used the subsequent 10 cycles of data for further analysis because the body movements were unstable at the beginning of a trial.

Data analysis
We defined several “movement reference points” (i.e., distinctive perceptual events that can be used to synchronize body movements with the metronome beats) for each movement. We analyzed the temporal relationship between these reference points and the beats for every cycle. The table below summarizes the reference points used in the following analysis.

These reference points were calculated from the movements of markers attached to the participants’ C7, ankles and toes. Thus, the experimental data stored in this database are the trajectories of these markers and the GRF data. In addition, we registered the timing of the extracted reference points for each movement.  

Table: Movement Reference Points for Four Target Movements

Symbol

Objective Criterion

Physical Event

Changement

GC

GP1

BB

GP2

GL

BT

GRF onset

GRF’s first peak

C7’s bottom point

GRF’s second peak

GRF offset

C7’s top point

Feet contact the ground.

Feet kick the ground to support the body.

Body is at the bottom.

Feet kick the ground to jump up.

Feet leave the ground.

Body is at the top.

Passé

BB

VBU

BR

VFU

FT

VFD

BF

VBD

C7’s bottom point

C7’s peak upward velocity

Offset of C7’s upward velocity

Ankle’s peak upward velocity.

Ankle’s highest point

Ankle’s peak downward velocity

Onset of C7’s downward velocity

C7’s peak downward velocity.

Body is at the bottom.

Body moves up the fastest.

Body has ridden on tiptoe.

Working toot goes up fastest.

Working foot is at the top.

Working foot goes down fastest.

Body starts to come down from the tiptoe.

Body moves down the fastest.

Jeté

FLS

VR

FR

VL

FLE

Onset of ankle’s velocity

Ankle’s peak rightward velocity

Ankle’s rightmost point

Ankle’s peak leftward velocity

Offset of ankle’s velocity

Working foot starts to move rightward (outwards).

Working foot moves rightward (outwards) fastest.

Working foot reaches the rightmost position.

Working foot moves leftward (inwards) fastest.

Working foot returns to the starting position.

Tendu

FRS

VL

FL

VR

FRE

Onset of toe’s velocity

Toe’s peak leftward velocity

Toe’s leftmost point

Toe’s peak rightward velocity

Offset of toe’s velocity

Working foot starts to move leftward (inwards).

Working foot moves leftward fastest.

Working foot is in the leftmost position.

Working foot moves rightward fastest.

Working foot returned to the rightmost position.