Do you hear the same? Cardiorespiratory responses between mothers and infants during tonal and atonal music

Abstract

This study examined the effects of tonal and atonal music on respiratory sinus arrhythmia (RSA) in 40 mothers and their 3-month-old infants. The tonal music fragment was composed using the structure of a harmonic series that corresponds with the pitch ratio characteristics of mother-infant vocal dialogues. The atonal fragment did not correspond with a tonal structure. Mother-infant ECG and respiration were registered along with simultaneous video recordings. RR-interval, respiration rate, and RSA were calculated. RSA was corrected for any confounding respiratory and motor activities. The results showed that the infants' and the mothers' RSA-responses to the tonal and atonal music differed. The infants showed significantly higher RSA-levels during the tonal fragment than during the atonal fragment and baseline, suggesting increased vagal activity during tonal music. The mothers showed RSA-responses that were equal to their infants only when the infants were lying close to their bodies and when they heard the difference between the two fragments, preferring the tonal above the atonal fragment. The results are discussed with regard to music-related topics, psychophysiological integration and mother-infant vocal interaction processes.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Illustration of a spectral analysis (multiple peak sounds within one tone) of a 55 Hz pitch tone.

A regular sound vibration is a complex tone that consists of a fundamental frequency (F0 or harmonic number 1, h1 or A1 on the Figure, i.e., most left peak) + a series of harmonics or partials (h2–16, other peaks). Together, they blend, giving the impression of one single tone. The frequency of each partial is a multiple of the F0 (55–110–165 Hz and so forth…). These multiple relations are expressed in ratios on the Figure. For example h3 (165 Hz) is related to h2 (110 Hz) with a ratio of 3∶2. When considering the harmonics h2–16 in relation to the F0, you obtain the illustrated frequency ratios (see on the bottom of the Figure). Van Puyvelde et al. (2010) observed that, during tonal synchrony, mothers and infants share a tonal center (which corresponds with F0/h1 and its octaviations) to which their other uttered pitches are related in the same fashion as the partials of a harmonic series are related to the fundamental frequency or F0 (i.e., the mothers and infants use the same ratios as pictured on the Figure). The partials of the tonal center are indicated by rectangles and the arrows show the frequency ratios with regard to this tonal center. For example h6 is related to h4 (ratio 6∶4 = 3∶2) and not h5 because h5 is not part of the tonal center (no octaviation of F0). On the right, an overview of the distribution of the ratios during tonal synchrony and their approximated music interval is given, with a distinction between high consonance (2∶1, octave; 3∶2, perfect 5; 5∶4 major 3) medium consonance (7∶4, minor 7; 9∶8, major 2) and dissonance (11∶8, triton; 13∶8, minor 6; 15∶8 major 7). The same ratios and distribution were used in the tonal fragment, i.e., 70% high, 25% medium consonance and 5% dissonance).

Figure 2. Mothers and infants listened to two music fragments.

One group of the mothers maintained close body contact with their infants. The other mothers were asked to take a seated position next to the infant without close body contact. The music stereo installation was placed 1 meter from the participants. The music stimulus was played at 60 db.

Figure 3. Illustration of the first 14 bars of the two music fragments to show the tonal structure and the disruption of tonality.

Fragment 1 (Tonal structure) is composed with the notes of the harmonic series C, i.e., C-G-E-Bb-D-F#. The ratios in relation to the tonal center C consisted of 70% high consonance (i.e., the notes C-E-G), 25% medium consonance (i.e., the notes Bb, D) and 5% dissonance (i.e., the notes, F#, G#, B). In Fragment 2 (Atonal structure), the harmonic series musical structure was absent.

Figure 4. Overview of RSA-responses before and after correction for respiratory and motor confounds in mother group and infant group.

Figure 5. Overview of the RSA-responses of mothers and infants in each group.