Vocal emotion expression across contexts, vocalization types, and species: Implications for general processes of vocal evolution Open Access

Schwartz, Jay (Spring 2020)

Permanent URL: https://etd.library.emory.edu/concern/etds/jw827c636?locale=en
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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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