Figure 1.
Spontaneous limb movements of infants when they listen to “Everybody” by The Backstreet Boys (music condition, Video S3) and those without any auditory stimulus (silent condition, Video S1).
(A) Typical limb trajectories during the music condition in an infant (ID1) in X, Y, and Z coordinates. (B) Mean square sum of right leg velocities and (C) relative proportion of the power spectrum density (PSD) around the musical tempo for right leg movements along the Y coordinate axis in ID1 (red), other infants (grey), and the group mean except for ID1 with standard deviation (SD) (black). (D) The right-foot position along the Y coordinate axis in ID1. He kicked more rhythmically during the music condition (red) than the silent condition (blue). (E) Power spectrogram of the right foot position along the Y coordinate axis in ID1. Relatively high PSD can be seen around the musical tempo (dashed line) in the music condition. (F) Mean synchronization index across moving sections (Methods for detail) in the music (red) and silent (blue) conditions. Error bars indicate standard errors (SE) across the moving sections.*p<0.01.
Figure 2.
Significant synchronization in right leg movements of ID1 during the music condition “Everybody” (108.7 BPM) (Video S3).
(A) Sound wave of the auditory stimulus (yellow) with the detected beat onsets (red vertical lines). (B) Observed (left) and phase-randomized (right) position data spos (t) along the Y coordinate axis when the infant moved continuously over a period of three seconds (defined as a moving section). (C) Instantaneous phase of the musical beat φmusic (t) calculated from the detected beat onsets. (D) Instantaneous phase of the motion φmotion (t). (E) Relative phase φrel (t) between motion and the musical beat. (F) Circular histograms of φrel (t). (G) Monte-Carlo statistics showed that the observed synchronization index (magenta line) was above the 95% confidence interval of the surrogate synchronization indexes (blue lines) calculated from the 10,000 phase-randomized position data: The observed movement was significantly synchronized to the musical beat.
Figure 3.
Spontaneous vocalizations of infants during the music condition “Go Trippy” by WANICO feat. Jake Smith (red) and in the silent condition where no auditory stimulus was present (blue).
Error bars indicate standard errors (SE) among the participants. (A) No significant difference was found in mean duration of vocalization per minute between the silent and music conditions (Wilcoxon signed-rank test, Z = 1.62, p = 0.11). (B) Typical time series of fundamental (F0, black lines) and formant frequencies (F1 and F2, cyan and magenta lines, respectively) within utterances. (C, D) Mean F0 and F1 was significantly higher in the music condition than in the silent condition (Z = 2.39, *p<0.05; Z = 2.06, *p<0.05, respectively). (E, F) There were no significant differences in mean F2 and SD of F0 (Z = 1.92, p = 0.06; Z = 1.16, P = 0.25, respectively). (G, H) SD of F1 and F2 were significantly higher in the music condition than in the silent condition (Z = 3.43, **p<0.001; Z = 3.48, **p<0.001, respectively).