Vocal emotion expression across contexts, vocalization types, and species: Implications for general processes of vocal evolution Open Access
Schwartz, Jay (Spring 2020)
Abstract
Research into the vocal expression of emotion has the potential to elucidate both the proximate mechanisms by which vocalizations are produced and perceived, and the ultimate processes by which communication systems evolve. Since Charles Darwin, researchers have hypothesized that emotion is crucial for vocal production in animals, culminating in a recent flourishing of research examining how emotional states influence the acoustic structure of vocalizations. These patterns of vocal emotion expression are broadly consistent across mammalian species, including humans, suggesting they have been conserved over evolutionary time. However, many taxa and vocalization types remain to be studied; in particular, little research exists comparing the effects of emotional states on vocal acoustics between multiple vocalization types within a species. In Study 1, I recorded and analyzed juvenile female rhesus macaque (Macaca mulatta) ‘coo’ and ‘scream’ vocalizations, occurring in disparate contexts. I compared the acoustic structure of each to the vocalizer’s emotional arousal, as inferred from stress hormones for coos, and agonistic intensity for screams. In both coos and screams, several parameters related to fundamental frequency (F0; commonly perceived by humans as pitch) correlated positively with arousal, suggesting that some of arousal’s effects on the voice are consistent across vocalization types and contexts. Thus some variation in vocal F0 appears linked to arousal and could, in theory, exhibit a correlated response to selection pressures favoring a broader arousal reaction—and vice versa. In Study 2, participants with and those without job-related experience with rhesus macaques listened to a subset of these vocalizations and indicated their perceptions of the intensity of the vocalizer’s emotion. While experience did affect accuracy of perceptions of macaque screams (but not coos), inexperienced and experienced participants alike showed significantly above-chance accuracy with both vocalization types. The F0 of coos and screams—indicated in Study 1 as a cue to emotional arousal—positively influenced participants’ perceptions of arousal from these vocalization types, suggesting evolutionary homology in the relationship between vocal F0 and emotional arousal. Collectively this work demonstrates the potential of vocal emotion expression research to elucidate general processes in the evolution of vocalizations, and of communication more broadly.
Table of Contents
CHAPTER I: GENERAL INTRODUCTION...1
1. The Proximate-Ultimate Distinction...2
2. Proximate (Mechanistic) Explanations for the Acoustic Properties of Vocalizations...5
2.1. Basics of Bioacoustics and Vocal Production...5
2.2. Variation Within and Between Vocalization Types...9
2.3. The Role of Emotion...11
2.3.1. Defining Emotion...11
2.3.2. Measuring Emotion in Animals...16
2.3.3. Vocal Emotion Expression: Effects of Emotion on Vocal Production and Acoustics...23
3. Animal Communication and Ultimate (Evolutionary) Explanations for Acoustic Properties of Vocalizations...30
3.1. The Sender-Precursor Model...30
3.2. The Receiver-Precursor Model...34
3.3. Environmental Pressures...36
4. Integrating Proximate and Ultimate Explanations: The Significance of Emotion for Vocal Evolution...37
4.1. Phylogenetic Inertia and Evolutionary Homology...38
4.2. Correlated Response to Selection...42
4.3. The Significance of Emotion for Correlated Response to Selection...44
5. The Evolutionary Potential of Vocal Emotion Expression Research...51
6. References...55
CHAPTER II: EXPRESSION OF EMOTIONAL AROUSAL ACROSS TWO VOCALIZATIONS TYPES IN RHESUS MACAQUES (MACACA MULATTA): INTEGRATING PROXIMATE AND ULTIMATE PERSPECTIVES…79
Abstract...80
Introduction...81
Methods...89
Subjects and Housing...89
Ethical Statement...90
Coo Recording, Preparation, and Selection...90
Scream Recording, Preparation, and Selection...93
Acoustic Analyses...96
Statistical Analyses...100
Results...102
Coos...103
Screams...107
Discussion...111
Comparing the Acoustic Correlates of Emotional Arousal in Coos and Screams...111
Acoustic Variation Within and Between Scream Classes...114
Methods for Measuring Emotional Arousal...117
Effects of Age...120
Conclusions...121
References...123
CHAPTER III: HUMANS ACCURATELY PERCEIVE EMOTIONAL AROUSAL FROM ACOUSTIC VARIATION WITHIN TWO RHESUS MACAQUE (MACACA MULATTA) VOCALIZATION TYPES...141
Abstract...142
Introduction...143
Methods...148
Ethical Statement...148
Participants...148
Stimuli...149
Procedure...153
Acoustic Analyses...155
Statistical Analyses...156
Results...158
Discussion...163
Accuracy and Experience...164
Acoustic Cues to Emotional Arousal...166
Emotional Arousal and Valence...169
Conclusions...170
References...171
CHAPTER IV: GENERAL DISCUSSION...179
Summary of Findings and Proximate Perspectives...182
Evolutionary Implications...184
Conclusions...188
References...190
Figures and Tables
Figure 1.1...7
Figure 1.2...50
Table 2.1...94
Figure 2.1...96
Table 2.2...97
Table 2.3...100
Table 2.4...102
Table 2.5...104
Figure 2.2...105
Figure 2.3...106
Table 2.6...107
Figure 2.4...109
Figure 2.5...110
Figure 3.1...160
Table 3.1...160
Table 3.2...161
Figure 3.2...162
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