Vocal Speed and Processing of Persuasive Messages: Curvilinear Processing Effects

Most work on indicators of vocal confidence (and social influence work more broadly) examines linear relationships between variables. However, in some domains curvilinear (i.e., accelerating or decelerating) relationships may provide greater clarity in understanding human speech patterns. We review mixed past work on vocal speed as a case study, wherein faster vocal speed has been shown both to bolster and inhibit persuasion (e.g., by impairing processing). Across six total studies (N_total = 3,958), we show that faster speed initially increases perceived source confidence and message processing but eventually the increase attenuates or reverses. Correspondingly, vocal speed has a decelerating relationship to participants’ processing of persuasive messages, as revealed by two main processes: argument quality effects on attitudes, and the correspondence between thought valence and attitudes. The present work highlights the potential value of high-powered examinations of curvilinear relationships in non-verbal phenomenon for which speed is likely to play a role.