First evidence of the acoustic correlates of cooperative behaviour: Men with lower‐pitched voices & greater pitch variations were more cooperative; however, testosterone did not influence cooperative behaviours

Does he sound cooperative? Acoustic correlates of cooperativeness. Arnaud Tognetti, Valerie Durand, Melissa Barkat‐Defradas, Astrid Hopfensitz. British Journal of Psychology, December 9 2019. https://doi.org/10.1111/bjop.12437

Abstract: The sound of the voice has several acoustic features that influence the perception of how cooperative the speaker is. It remains unknown, however, whether these acoustic features are associated with actual cooperative behaviour. This issue is crucial to disentangle whether inferences of traits from voices are based on stereotypes, or facilitate the detection of cooperative partners. The latter is likely due to the pleiotropic effect that testosterone has on both cooperative behaviours and acoustic features. In the present study, we quantified the cooperativeness of native French‐speaking men in a one‐shot public good game. We also measured mean fundamental frequency, pitch variations, roughness, and breathiness from spontaneous speech recordings of the same men and collected saliva samples to measure their testosterone levels. Our results showed that men with lower‐pitched voices and greater pitch variations were more cooperative. However, testosterone did not influence cooperative behaviours or acoustic features. Our finding provides the first evidence of the acoustic correlates of cooperative behaviour. When considered in combination with the literature on the detection of cooperativeness from faces, the results imply that assessment of cooperative behaviour would be improved by simultaneous consideration of visual and auditory cues.



Discussion

Several acoustic features influence the perception of how trustworthy and cooperative the speaker is (Belinet al., 2017; Knowles & Little, 2016; Montano et al., 2017; O’Connor& Barclay, 2017; Oleszkiewicz et al., 2017; Ponsotet al., 2018; Tigue et al., 2012; Tsantani et al., 2016). Their influence could stem from the pleiotropic effect of testosterone on both acoustic features and cooperative behaviours (O’Connor & Barclay, 2017). It is unknown, however, whether acoustic features are associated with actual cooperativebehaviour and whether testosterone mediates this association. In this study, we presentevidence that both vocal pitch and its variations are related to cooperative behaviour in anincentivized social-dilemma game: the public good game. However, no effect oftestosterone level on cooperation, or on any of the other acoustic features studied, wasfound. Overall, ourstudy providesthe first evidence of the existence of acoustic correlates of cooperativeness.

Specifically, our results indicate that men’s contributions to the public good aresignificantly and negatively associated with fundamental frequency and significantly andpositively with its variations. When we compared the acoustic traits between conditional cooperators and free-riders (the two main categories as defined in Fischbackeret al.(2001)), we found that conditional cooperators exhibit significantly higher pitch variations than free-riders. Taken together, our results suggest that highly cooperative men have deeper voices and exhibit greater variations in their intonation compared to less cooperative men.The present results are consistent with the only previous study examining jointly the influence of vocal pitchand its variations on the perception of a speaker’s cooperativeness (Knowles & Little, 2016). Indeed, Knowles and Little (2016) found that male voices wereperceived as the most likely to cooperate when they exhibited high pitch variations in combination with a low pitch (although it was found for women’s but not for men’sratings). Vocal pitch and its variation are, thus, associated in the same way with bothcooperative behaviours and perceived cooperativeness. It, therefore, indicates that inferences of cooperativeness from voices might actually facilitate the detection ofcooperative partners. This sets the ground for future research, namely whether particular ombinations of acoustic traits influence ratings of cooperativeness and to which degreethese acoustic cues of cooperativeness are reliable or could be manipulated throughconscious control of the speaker (e.g., by lowering voice pitch or by increasing speech’sintonation).Behavioural decisions in the public good games (contributions to the public good) andin the trust game (amounts sent to the other player) are highly correlated (Galizzi & Navarro-Mart ınez, 2018; Peysakhovich, Nowak, & Rand, 2014), which suggests a strongassociation between cooperativeness and trustworthiness. Hence, similarly to cooper-ativeness, vocalpitchand itsvariationsarealso likelytobe used ascues oftrustworthiness.

In fact, both acoustic features influence perception of how trustworthy a speaker is. For example, lower-pitched male voices and voices with high pitch variations are perceived asmore trustworthy in general (Belinet al., 2017; Oleszkiewicz et al., 2017; Schirmer et al.,2019; Tsantaniet al., 2016) or when trust is linked to the political context (Klofstadet al.,2015, 2012; Tigueet al., 2012). It remains unknown, however, whether these acousticfeatures correlate with actual trustworthiness, and not only with perceived trustworthiness.The existence of vocal cues of cooperativeness could stem from the pleiotropic effectof testosterone on both cooperative behaviours (Burnham, 2007; Diekhofet al., 2014; Reimers & Diekhof, 2015; Takagishiet al., 2011) and vocal pitch (Dabbs & Mallinger,1999; Evanset al., 2008; Putset al., 2012). As testosterone has immunosuppressive effects (immunocompetence handicap hypothesis: Folstad & Karter, 1992; Rantalaet al., 2012;but see: J. Nowak, Pawłowski, Borkowska, Augustyniak, & Drulis-Kawa, 2018), men with(costly) lower pitch might benefit from a higher biological quality (Arnocky, Hodges-Simeon, Ouellette, & Albert, 2018; Hodges-Simeonet al., 2015). In addition, they may also be more socially dominant (Puts et al., 2012; Puts, Gaulin, & Verdolini, 2006; Putset al.,2007). Accordingly, because of their underlying qualities, including access to resources,men with lower pitch would be more cooperative than men with higher pitch becausethey could better afford the costs associated with cooperative behaviours while receiving reputational benefits (Raihani & Smith, 2015; Sylwester & Roberts, 2010; Tognetti,Berticat, Raymond, & Faurie, 2012; Tognettiet al., 2016). This condition-dependent mechanism could ensure the reliability of the vocal cues of cooperativeness. However, in the present study testosterone levels did not seem to affect cooperation or any of theacoustic features studied. Testosterone is a multiple-effect hormone which is influencedby numerous biological and environmental factors and pathways. As such, it is generally difficult to correlate testosterone levels to other biological or behavioural traits. Inaddition, we could only collect one sample of saliva for hormonal assays, which might notaccurately reflect a participant’s basal testosterone level.

Although the present study retains many strengths, it is also subject to several limitations. In particular, it is the first to investigate the existence of acoustic correlates ofcooperativeness in speech production. However, the investigation is restricted to Frenchmen. To provide broader conclusions, it should not only be extended to women, but toother populations as well. In addition, we did not conduct a perceptual study using ourrecordings to examine whether listeners use acoustic features as a social cue in abehavioural economic task. Indeed, we recorded individuals’ free speech due to itsstronger ecological validity (Puts e tal., 2007; Suireetal., 2018), but this type ofrecordingsis not suitable for perceptual studies, as recordings roughly differ in duration and semanticcontent. Finally, we used state-of-the-art methodology in economics to quantify andcategorize individuals according to type (Fischbacheret al., 2001). However, wecompared two categories with unbalanced sample sizes (NFree-rider=11 vs.Nconditionalcooperator=44) and the sample size of the free-riders was limited (although its proportion(18%) mimics the proportion found in the general French population; Frey, 2017). Hence,we cannot exclude the possibility that the acoustic differences found between free-ridersand conditional cooperators arose from this specific and particular sample of 11 free-riders. It seems, nevertheless, unlikely as the results found using this categorization arequalitatively similar to the ones we found using a continuous measure of cooperativeness(i.e., contributions to the public good).

To conclude, the present study provides evidence that at least two acoustic features(vocal pitch and its local variations) could be used as cues of cooperativeness. Facial cuesenable individuals to discriminate between high and low cooperative individuals with anabove chance accuracy (Bonnefon et al., 2013, 2017; Fetchenhauer et al., 2010; Little et al., 2013; Oda, Naganawa, et al., 2009; Reedet al., 2012; Stirrat & Perrett, 2010, 2012;Tognettiet al., 2013) but the accuracy of face-based cooperation detection is rather low (Bonnefon et al., 2017). Hence, by highlighting the fact that cooperativeness is advertisedby several cues across multiple sensory modalities, our findings pave the way for further investigations examining whether the assessment of cooperative behaviour is improved by simultaneous consideration of both visual and auditory cues.