Spectro-temporal acoustic elements of music interact in an integrated way to modulate emotional responses in pigs

Abstract

Music is a complex stimulus, with various spectro-temporal acoustic elements determining one of the most important attributes of music, the ability to elicit emotions. Effects of various musical acoustic elements on emotions in non-human animals have not been studied with an integrated approach. However, this knowledge is important to design music to provide environmental enrichment for non-human species. Thirty-nine instrumental musical pieces were composed and used to determine effects of various acoustic parameters on emotional responses in farm pigs. Video recordings (n = 50) of pigs in the nursery phase (7-9 week old) were gathered and emotional responses induced by stimuli were evaluated with Qualitative Behavioral Assessment (QBA). Non-parametric statistical models (Generalized Additive Models, Decision Trees, Random Forests, and XGBoost) were applied and compared to evaluate relationships between acoustic parameters and pigs' observed emotional responses. We concluded that musical structure affected emotional responses of pigs. The valence of modulated emotions depended on integrated and simultaneous interactions of various spectral and temporal structural components of music that can be readily modified. This new knowledge supports design of musical stimuli to be used as environmental enrichment for non-human animals.

Figure 1

Musical stimulation arrangement. Musical pieces were randomly presented, considering interspersed rest periods.

Figure 2

Plots of loadings for the 17 QBA analyzed terms. (A) Terms plotted on the first principal components PC1 (positive high arousal index) and PC2 (negative high arousal index). (B) Terms plotted on PC1 and PC3 (positive low arousal index).

Figure 3

Coordinates of litter emotional states to each piece of music.

Figure 4

Contour plots for predictive acoustic parameters, derived from a GAM model. The central pink area determines explicit ranges where specific acoustic parameters were related to each emotional response (A). Positive high arousal index. Pulse values between 110 and 130 BPM, with 3 and 4 instruments, induced more positive responses. (B) Negative high arousal index. A combination of any HFC values, with levels of spectral deviation < 3000 were associated with higher values for this index. (C) Positive low arousal index. Pulse values < 120 bpm and 4 to 6 instruments were associated with emotional responses included in this index.