Collaborative Research: Psychological and Behavioral Preparatory Responses to Male Aggressive Vocal Signaling

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Personal aggression has serious consequences yet often starts with seemingly trivial verbal disputes ("I don't like your tone"). These verbal conflicts are common between both acquaintances and strangers. Some of these conflicts quickly end with one party standing down, but others escalate verbally to physical, even fatal, fights. What role do vocal qualities (not what people say, but physical aspects of the voice) play in determining whether a verbal dispute becomes a fight? Research on other animals indicates that vocal qualities often give information about physical strength and aggressive intentions, which can predict fight outcomes and thus affect an individual's motivation to fight. For example, previous research shows that men with lower pitched voices are judged as being more likely to win fistfights than men with less deep voices. In this case, pitch is a way to manipulate "signal intensity", which evolutionary theory suggests would convey important cues useful to a potential attacker. An intense signal conveys the speaker is more motivated to aggress or is physically stronger than would a weaker signal. Theory suggests that the listener's likelihood of retreating or attacking should be affected by perceptions of the voice, but research has not yet tested those hypotheses in humans. Thus this project builds on previous findings about perceiving voices, to extend it to people's preparation to aggress. The investigators use experiments to create mildly competitive situations and examine whether signal speaker's vocal features affects listeners' aggressive inclinations. Understanding how vocal qualities can reduce or increase aggression will help professionals who are regularly exposed to violence (e.g., police officers) to navigate danger, and inform intervention programs that aim at curtailing violence.This project tests key hypotheses drawn from M. Enquist's retaliation-cost model, a leading model of aggressive communication in animals. The investigators will measure people's psychological and physical responses to vocal features that serve as strong or weak signals to aggressive intent or aggressive ability. In three sets of experiments, the investigators will manipulate whether the signal intensity of a male speaker's voice is strong or weak. Experiment Set 1 also manipulates facial dominance of the speaker, and whether the topic of his expressed anger is of significant or minimal value. Interactions of the three manipulated variables are predicted to affect listener's judgments about aggressive intent. Experiment Set 2 will test how listeners' physical strength and cues of competition for mates influence their attention to and memory of the speaker. Experiment Set 3 extends the Set 2 by focusing on listeners' aggressive thinking and preparation (e.g., immediate increases in physical strength) in response to hearing signals of strong versus weak intensity. To enhance the validity of the project, the investigators will recruit police officers to participate in Experiment Set 1. To facilitate cross-cultural comparisons, the investigators will perform parallel experiments in China, a country with much lower homicide rates than the U.S. This project will provide a deeper understanding of the evolution and function of voice pitch in aggressive interactions.