Regularity in speech rhythm as a social coalition signal

First published: 01 August 2019Regular rhythm facilitates audiomotor entrainment and synchronization in motor behavior and vocalizations between individuals. As rhythm entrainment between interacting agents is correlated with higher levels of cooperation and prosocial affiliative behavior, humans can potentiallymap regular speech rhythmonto higher cooperation and friendliness between interacting individuals.We tested this hypothesis at two rhythmic levels: pulse (recurrent acoustic events) and meter (hierarchical structuring of pulses based on their relative salience).We asked the listeners to make judgments of the hostile or collaborative attitude of two interacting agents who exhibit either regular or irregular pulse (Experiment 1) or meter (Experiment 2). The results confirmed a link between the perception of social affiliation and rhythmicity: evenly distributed pulses (vowel onsets) and consistent grouping of pulses into recurrent hierarchical patterns are more likely to be perceived as cooperation signals. People are more sensitive to regularity at the level of pulse than at the level of meter, and they are more confident when they associate cooperation with isochrony in pulse. The evolutionary origin of this faculty is possibly the need to transmit and perceive coalition information in social groups of human ancestors. We discuss the implications of these findings for the emergence of speech in humans.The authors acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (MINECO), through the “Severo Ochoa” Programme for Centres/Units of Excellence in R&D (SEV-2015-0490) to the BCBL, from European Commission as Marie Skłodowska-Curie fellowDLV- 792331 to L.P., fromMinisterio de Ciencia E Innovacion by grant PSI2017-82563-P to A.G.S., and grant RTI2018-098317-B-I00 to M.O