by BEATRICE BRETHERTON, KIA NG, LUKE WINDSOR, ROGER WATT
Background
Human physiology is highly sensitive to music. Activity in the autonomic nervous system has been found to be influenced by numerous musical parameters, including rubato, dynamics and tempo (Mikutta et al., 2013; van der Zwaag, Westerink, & van den Broek, 2011). The autonomic nervous system controls the functioning of the heart and is composed of two sub-systems: the sympathetic nervous system which mobilizes energy resources, and the parasympathetic nervous system which conserves energy resources (Porges, 2011). The influence of musical parameters on activity within these subsystems can be measured using heart rate variability. Heart rate variability quantifies the amount of variance in the time interval between consecutive heartbeats as well as changes in activity within the sympathetic and parasympathetic nervous systems (Bilchick & Berger, 2006). In this study, heart rate variability was used to explore the influence of two excerpts of music on the autonomic nervous system.
Music also has a strong relationship with embodied motion. For instance, different musical parameters have been found to be associated with specific forms of movement (Burger, Thompson, Luck, Saarikallio, & Toiviainen, 2014). A wide range of techniques has been used to measure embodied motion, including optical motion capture systems and motion curves (Burger et al. 2014; Repp, 1992). A novel approach to measuring embodied musical motion was developed in the study; this involved doodling on an interactive writing pad whilst listening to music.
Aims
The study aimed to explore the cross-modal interactions between musical parameters: heart rate variability and doodles. The study sought to:
1. Examine the associations between musical parameters and sympathetic activity patterns
2. Determine whether a particular type of doodling better suited one musical stimulus over another
3. Explore potential musical parameters responsible for making one type of doodling better suited to a particular musical stimulus
4. Determine whether an interaction between music, heart rate variability and embodied motion may exist
Method
Participants
In total, fourteen Caucasian individuals (seven males) ranging from 21-56 years of age participated in the study. The study was approved by the University of Stirling’s Psychology Ethics Committee.
Apparatus and materials
The first sixty seconds of two pieces of music were presented to participants: ‘Always with me, always with you’ by Joe Satriani; and McGibbon’s ‘Minuet in A’ performed by Northumbrian Exchanges. Photoplethysmography was used to detect participant heartbeats and to derive heart rate variability. This involved attaching an infrared sensor to the little finger of the non-dominant hand. Doodles were captured by moving a wireless pen on an interactive USB writing pad and visualised on a computer screen. The doodle and heart rate data tracked participant responses to changing musical parameters from second to second.
Procedure
At the start of each condition participants experienced an adaptation period of one minute. As soon as participant heart rates had stabilised, heart rate was recorded and the study began. All participants experienced two conditions: linear doodling, which involved doodling lines whilst listening to the two excerpts; and curvilinear doodling, which involved doodling curves whilst listening to the two excerpts. The order of conditions and excerpts was randomised. Heart rate recording was stopped at the end of each condition to allow participants a brief break.
Data analysis
Spectral density analysis was performed on the heart rate data to derive a low frequency component of heart rate variability centred on 0.1Hz, well below respiration rate. Changes in power within the low frequency component were analysed for the purposes of the study. The low frequency component is considered to represent sympathovagal activity, with increases in power reflecting physiological arousal and decreases in power reflecting physiological relaxation. The time trace and resultant curves of the doodle data were also analysed for both excerpts in both conditions. Audio files of the excerpts were analysed using the MIRToolbox and the harmonic structure of the excerpts was ascertained via analysis of the scores.
Results
Heart rate variability
The graphs below show the low frequency response, relative to a baseline (activity level at the moment the music began), averaged across participants. Sympathetic activity was lower overall for curvilinear doodling in the Satriani excerpt (see Figure 1). In addition, a small peak in power occurred between 11 and 26 seconds, for curvilinear doodling, which coincided with a repeat of the first four bars of introductory percussion. Since participants may have expected the entry of the soloist to occur after these first four bars and this failed to happen, the sudden increase in activity could be associated with the violation of listener expectations. The next small peak in power occurred at 26 seconds; this peak may represent the fulfilment of listener expectations as it coincides with the entry of the soloist playing the melody. The lowest troughs in activity occurring at 40 seconds coincided with a tonic chord and were present for both linear and curvilinear doodling.
Figure 1. Graph showing changes in sympathetic activity over time, for the Satriani excerpt for linear and curvilinear doodling
Sympathetic activity was also lower overall for curvilinear doodling in the McGibbon excerpt (see Figure 2). A rapid increase in power at the beginning of the piece was seen in both conditions and may be attributed to a general uncertainty about the music that resolves in the first few seconds. At 15 seconds, patterns in power diverged for the two conditions. This suggests that events occurring in the music at around 15 seconds relaxed listeners engaged in curvilinear doodling and aroused listeners engaged in linear doodling. An analysis of the music identified a repeat of the preceding bars, indicating that familiarity may have mediated the interaction between sympathetic activity and type of doodling.
Three successive peaks in activity for curvilinear doodling were also identified. The first emerged between 24 and 36 seconds, the second between 36 and 48 seconds, and the third between 48 and 60 seconds. All three peaks were 12 seconds in duration and had a six second increase followed by a six second decrease. The increase coincided with movement away from the tonic and the decrease coincided with movement towards the tonic. Although similar consecutive peaks were seen for linear doodling, they were not as clear as those occurring in the curves condition. This perhaps suggests that curvilinear doodling was better suited to the McGibbon excerpt.
Figure 2. Graph showing changes in sympathetic activity over time, for the McGibbon excerpt for linear and curvilinear doodling
Doodles
In both conditions participants produced doodles that were characteristic of linear doodling for the Satriani excerpt. Interestingly, participants also produced doodles that were characteristic of curvilinear doodles in both conditions for the McGibbon excerpt. This suggests that the Satriani excerpt was better suited to linear doodling, and the McGibbon to curvilinear doodling.
An analysis of the audio files found that the Satriani piece had a more stable tempo and clearer pulse compared to the McGibbon. Since a relatively stable tempo and clear beat facilitate the precise anticipation of consecutive beats, this may have enabled participants to know when to change direction when doodling, and may explain why linear doodling better suited the Satriani. In contrast, curvilinear doodling does not require a stable tempo or clear beat as no sudden change in direction is needed at a single moment in time. Therefore, curvilinear doodling may have been better suited the McGibbon piece because this type of doodling is more amenable to rhythmically ambiguous music.
Conclusions
In conclusion, sympathetic activity increased when music departed from the tonic and when listeners’ musical expectations were violated. Sympathetic activity decreased when music returned to the tonic and when musical ideas were repeated. This suggests that harmonic structure and musical expectations may mediate autonomic nervous system activity when listening to music. Linear doodling was better suited to the Satriani due to the presence of a relatively stable tempo and clear beat. In contrast, curvilinear doodling was better suited to the McGibbon as there was greater variation in the tempo and a weaker beat. The findings point to the presence of an interaction between sympathetic activity, doodling and music, as linear doodling to the rhythmically ambiguous McGibbon excerpt resulted in higher sympathetic activity than linear doodling. In order to develop a more comprehensive account of the influence of music on the autonomic nervous system and embodied motion, other cardiovascular and motion tracking measures are required. In turn, this should facilitate greater understanding of the cross-modal interactions that exist between music, the autonomic nervous system and embodied motion.
Notes
Address for correspondence: Beatrice Bretherton, School of Music, University of Leeds, LS2 9JT.
Email: mcbeb@leeds.ac.uk.
References
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